Introduction
In modern agriculture, seed is a vehicle to deliver almost all agriculture-based technological innovations to farmer. The availability, access and use of seed of adaptable modern varieties is, therefore, determinant to the efficiency and productivity of other packages (irrigation, fertilizers, pesticides) in increasing crop production to enhance food security and alleviating rural poverty in developing countries. The future for wheat seed production appears to be mixed .Wheat is a high-volume, low-profit seed crop and has been produced primarily by heavily subsidized government seed programmes.
With privatization and liberalization, many of these programmes are at risk of being closed down. The private sector, however, may not focus on wheat seed due to its characteristics (self-pollinating, high-volume and low-profit). If private seed enterprises exist, they consider wheat seed to be of secondary importance. Furthermore, in most countries there has been no ongoing effort to promote the use of improved seed by wheat farmers, and no significant breeding developments have recently taken place to increase yield and quality. Since wheat is a self-pollinating crop and the grain can be used as seed, farmers tend to replant their own seed.
It is, therefore, expected that in the future the large majority of resource-poor, small-scale farmers in many developing countries will have to rely on seed saved from the previous harvest.
In the developed world, declining world market prices for grain do not encourage farmers to produce wheat. Moreover, there have been no widespread disease outbreaks, which make seed treatment (and thus purchase of certified seed) necessary.
Countries in Europe and the United States are attempting to reduce subsidies, which will result in further unwillingness to invest. On the other hand, there are possibilities in developing countries for major increases if significantly improved varieties appear on the market, disease outbreaks occur and organized promotional efforts emphasize maximum production efficiency including improved seed.
Commonly cultivated wheat species
There are 7 in the world, only 4 is important in India, they are:
1. Common wheat ( Triticum vulgare / aestivum) : A hexaploid species that is the most widely cultivated in the world. it is also called as Bread wheat ,Most suited for chapati and bakery, Cultivated throughout India .Common wheat may be sub-divided:
ü Hard red winter wheat: commercial class
ü Hard red spring: where winter is too severe, high protein and excellent bread making characteristics
ü Soft red winter: grown in humid conditions, grains are soft, low protein, flour more suitable for cakes, cookies
ü White wheat: mainly for pasty purpose
2 . Duram (T. durum) : Also called Macroni wheat , The only tetraploid form of wheat widely used today, Best suited for noodles, vermicelli, it has Spring habit and cultivated in Central & Southern India.
3.Emmer wheat (T. dicoccum) tetraploid species , Winter / spring wheat , it is suitable for TN, Preferred for granular preparation, mostly grown in Gujarat, Maharastra, AP & TN.
5. Short wheat (T. sphaerococcum) it is known as Indian dwarf wheat , Practically it has gone out of cultivation due to low productivity. In a small extent it is grown in North India and West Pakistan for local consumption.
6. Einkorn - (T. monococcum) A diploid species with wild and cultivated variants. One of the earliest cultivated, but rarely planted today.
7.Spelta - (T. spelta) Another hexaploid species cultivated in limited quantities.
SEED CLASSES
Seed production follows a generation system to ensure that all seed that is marketed to farmers originates from a known source (breeder seed). When a variety is officially released, the small amount of breeder seed received from the breeder (agricultural research centre) is multiplied through a number of generations before it becomes available to the farmers in larger quantities as certified seed. Each generation is produced under strict supervision and must meet seed quality standards. The number of generations that are allowed after breeder seed depends on the mode of reproduction of the crop, risk of contamination, multiplication ratio and quantity of the seed required. For wheat, four to five generations are commonly used.
Different generation schemes exist which vary very little, particularly in nomenclature. The procedures followed are essentially the same. The Organisation for Economic Cooperation and Development (OECD) generation scheme is used as outlined below:
Breeder seed is the initial source of seed and is usually produced by the breeder. It is the source for the production of pre-basic or basic seed.
Pre-basic seed: is the progeny of the breeder seed and is usually produced under the supervision of a breeder or his designated agency. This generation is commonly used for crops that have low multiplication ratios and where large quantities of certified seed are required.
Basic seed: is the progeny of breeder or pre-basic seed and is usually produced under the supervision of a breeder or his designated agency and under the control of a seed quality control agency.
Certified seed: is the progeny of basic seed and is produced on contract with selected seed growers under the supervision of the seed enterprise, public or private. Certified seed can be used to produce further generations of certified seed or can be planted by farmers for grain production.
Breeder seed production is not monitored by the seed certification agency, while basic seed and certified seed are covered in the seed certification scheme. The seed quality control agency verifies the quality both in the field and in the laboratory and certifies that the seed meets the national standards. Such classes of seed are known as certified. It is important to note that all certified seed classes relate to a breeder seed through one or more generations.
Some developing countries, where natural disasters such as drought are a common phenomenon, recognize a 'commercial seed' class to meet seed shortages in emergency situations. In such cases, the standards for certified seed are often lowered and accepted for distribution to farmers to overcome seed shortages. In other situations, commercial seed is simply a grain used as seed after laboratory testing for some quality attributes, such as purity and germination.
Variety maintenance and breeder seed production
Upon release of a new variety, a breeder will make available a small quantity of seed stock that is very pure and represents the variety. This stock is referred to as parental material and forms the basis of any future maintenance and seed multiplication of the variety (Laverack, 1994). Laverack defines maintenance as "the perpetuation of a small stock of parental material through repeated multiplication following a precise procedure". For wheat, an ear-to-row (Plate74) method is recommended, where a number of ears (depending on the total quantity of certified seed required) that are true-to-type are selected, threshed separately and then planted in individual rows. During the entire growth period, the rows are inspected regularly, and any row with off-types or deviants is discarded. Ears are selected from the remaining rows to repeat the cycle, which is usually referred to as maintenance. The remaining rows are bulk harvested, and the seed is called breeder seed. In India, for example, 1 000 plants are used for wheat variety maintenance (Singh, 1985). Each year the cycle is repeated to provide a regular supply of breeder seed for further multiplication to basic seed and then to certified seed. Maintenance and breeder seed production is the responsibility of the breeder or the institution that developed the variety. In many developing countries, maintenance is seldom carried out properly, and the responsibility is often taken over by seed production organizations. Some national seed programmes (e.g. Ethiopia) have established special farms to produce early generations (pre-basic and basic seed) to maintain quality and availability.
Planning for Seed production
New improved varieties developed by NARSs should be multiplied and made available to farmers in the shortest possible time to realize the benefits of investments in agricultural research. Appropriate seed production techniques coupled with strict quality control measures ensure that varietal purity and identity is maintained, which is the cornerstone of the entire seed program. The rate at which the variety is multiplied and accessed restricts the availability of seed and its adoption and rapid diffusion through formal or informal channels. Most farmers have a tendency to save their own seed of self-pollinating crops such as wheat compared to open-pollinated crops or hybrids where the risks of contamination and decrease in yield are higher. The seed renewal rate, the frequency in which farmers purchase certified seed of the same variety from the formal sector, varies between the types of seeds, crops, production environment sand socio-economic factors.
The multiplication factor can be defined as the amount of seed harvested from each quantity of seed sown. It differs from crop to crop, but is largely dependent on climate, physical factors (soil fertility, etc.) and agronomic management.
New varieties, after they enter commercial production, may lose their genetic potential or become susceptible to pests over time, which requires their replacement. Moreover, the varieties may also be exposed to genetic, mechanical and pathological contamination during the seed multiplication process. There is a practical need to limit the number of generations that the seed is multiplied after breeder seed.
For each generation, it is important to make an accurate estimate of the seed that needs to be produced every year. The total requirement depends on: (i) crop area planted; (ii) seed renewal rate; (iii) seed rate; (iv) multiplication ratio; and (v) number of generations. When planning seed production, the rates of rejection during field inspection, processing and laboratory testing should also be considered. Furthermore, a certain amount of carry-over seed should be taken into account, particularly for early generation seed. Precise estimates of seed demand are difficult because several factors, such as weather conditions and socio-economic factors, influence farmers' decisions on which crop to grow the next year. In case of wheat, farmers may prefer to keep own-saved seed for a longer period than the anticipated seed renewal rates of four to five years. The seed demand of new varieties is even more difficult to estimate and depends on the adoption rate, which in turn is influenced by several technical, institutional, economical and sociological factors.
Production arrangements
Generally, early generations (breeder and pre-basic seed) are produced on agricultural research farms and basic seed on specialized seed farms, while certified seed is more conveniently and economically produced by farmers who are contracted by the seed enterprise (public or private). Farmers' cooperatives and associations are often involved in certified seed production. The seed enterprise provides technical guidance and advice to growers on various aspects of seed production, such as planting, roguing and harvesting, as well as monitoring and supervising field operations. The seed quality control agency inspects the fields and tests the seed in the laboratory.
In wheat, seed and grain crop production follow rather similar operations. The end product can either be used for consumption or for planting. Such similarity can easily lead to mixing seed and grain during planting, harvesting, transportation and storage. Seed production should be strictly monitored, and seed producers should be quality conscious. In developing countries, farmers are rigorously selected before they become seed growers.
In many developing countries, the availability of experienced seed growers is limited, and seed organizations provide considerable support. A village seed production scheme, which groups adjacent fields for seed production, will help to overcome problems of isolation distances and supervision when contracting smallholder farmers for seed production.
The cost of seed production is higher than the cost of producing grain for consumption because it involves extra operations to maintain quality. Thus seed growers incur additional costs in field operations and management and must be paid a premium. In case of wheat, the additional premium paid over the grain price ranges from 10 to 20 percent.
Land selection Wheat can be successfully grown in most parts of the world, both in tropical and temperate environments and on all soil types that are well drained and productive. Seed (certainly breeder seed) should be produced in areas: (i) where the variety is adapted; (ii) where soil conditions are optimal (to achieve a high multiplication ratio); and (iii) where climatic conditions are reliable to avoid loss due to natural hazards (flooding, drought, frost, etc.). The early generations should possibly be planted at two different locations to reduce the risk of losing the complete generation.
In some tropical countries, there is a high risk of rain coinciding with harvest time. Rainfall at maturity delays harvesting, causes sprouting and predisposes the crop to fungal attack, resulting in poor seed quality, i.e. reduced viability and vigour. Selection of appropriate sites is very essential to produce quality seed.
Previous cropping
The crop should be planted on a field with a known history to avoid contamination from volunteer plants, noxious weeds and soil-borne diseases that are potentially seed transmitted. The minimum number of years that is allowed between the planting of two seed crops (or seed and grain crop) is usually prescribed by the national seed regulations. Examples of requirements for previous cropping in countries in West Asia and North Africa are provided in the WANA Secretariat (1995).
A wheat seed crop should never immediately follow wheat, unless the wheat crop in the previous season was of the same variety and of the same or higher generation. For basic seed, it is often recommended that the field should not have been planted with wheat or other small grain crops for at least two consecutive years. For certified seed, no wheat crop should have been grown in the previous year.
A suitable crop rotation plays an important role in pure seed production. For example, a two-year rotation for flag smut and seed gall nematode is suggested where applicable. For wheat, previous cropping could be legumes, vegetables or clean fallow, but other cereals (barley, oat, rye and triticale) and forage crops (oat) should be avoided.
Weeds
Seed contaminated with weeds could be the means for introduction and dissemination of noxious weeds. Mohamed (1996) mentioned that the introduction of wild oats in wheat in Egypt is attributed to contaminated seeds. Therefore, heavily infested fields with noxious weeds should be avoided. Unfortunately, fields in many countries are infested with wild oats (Avena fatua, A. sterilis and A. ludoviciana), noxious weeds that are spread almost all over the world and are difficult to eradicate. Avena fatua has no resistance to frost, and it is only problematic in summer wheat. In West Asia and North Africa (WANA), the problem is mainly A. sterilis.
Worldwide, a 10 percent potential yield loss in cereals is due to weeds, even with currently used control measures (Koch and Hess, 1980). In wheat, Tanner and Sahle (1993) cited that the use of clean seed had a significant effect on grain yield compared to weeding by hand or hoe.
For land selection, the most essential pre-requisite is the selection of clean fields that are properly rotated and known to be free from contaminants.
Planting and Cultural Practices
Preparation of Seedbed
Seedbed preparation is the same as for a grain crop. Wheat does not suppress weeds sufficiently and needs a clean, weed-free seed-bed for planting (Doerfler, 1976). In Sudan, weed competition studies on wheat showed that if weeding is not carried out between two and four weeks after sowing the yield is reduced by 20 percent (Mohamed, 1996).
Planting method
Planting with an automatic drill is recommended but not essential. However, row-planting has an advantage over broad-casting, as it requires less seed and facilitates mechanized weed control, roguing and field inspection (Galanopoulou et al., 1996). Roguing lanes (empty rows at intervals) should be left, which could be used by the seed grower to walk through the field when roguing and inspecting the crop, as well as for spraying the crop.
Deep sowing delays emergence, resulting in weaker seedlings, reduced emergence and poor tillering and yield. Varieties with short coleoptile length, particularly semidwarf varieties, suffer most compared to varieties with longer coleoptile length (Perry and Hillman, 1991).
Seed rates
The optimum seed rates for wheat vary with variety, location and method of planting. For seed production fields, a lower seed rate may be recommended because lower seed rates lead to higher multiplication factors (Nelson, 1986) but to lower yield per unit area . Higher multiplication factors lead to rapid seed increase (more seed harvested per kilogram of seed planted), and farmers will benefit from the improved variety earlier. Low seed rates do not only increase the multiplication factor, but also often improve seed quality because a lower number of plants per unit of land receive better nutrition, thus producing better quality seed.
In practice, very low seed rates are not used. Lower seed rates may be used when planting early generations, but certified seed is planted at the normal or slightly lower seed rate. For certified seed, acreage becomes too large to be closely monitored and thus the risk of reduced yield is too high.
Seed size
In wheat, seed size is positively correlated with seed vigour: larger seeds tend to produce more vigorous seedlings (Ries and Everson, 1973). Larger seeds of spring wheat produced higher yields than smaller seeds under late-sown conditions (Singh and Kailasanathan, 1976), but not under optimum management conditions (Kalita and Choudhury, 1984). Similarly, Khah et al. (1989) found that low-vigour spring wheat seed produced lower yields only when it resulted in low plant populations or when planting was later than normal. However, Mian and Nafziger (1992) have found that seed size has little effect on emergence of soft red winter wheat.
Fertilization
Fertilizer application to seed crops should be based on local recommendations. A well-balanced supply of nitrogen, phosphorus and potassium (NPK) is essential for seed production as it has an influence on seed development and thereby on seed quality. Phosphorus is essential for enhancing seed maturity and K for seed development. Ascher et al. (1994) concluded that seed nutrition combined with soil nutrition gave better yields and better seed quality. For example, cereals (wheat, barley and oats) grown from seed with a high P concentration gave 20 percent more yield than with low P, with a critical concentration of 0.30 percent for wheat seed (Perry and Hillman, 1991). Ngugi (1992) reported that the use of compound fertilizers with sulphur (S) and calcium (Ca) gave higher grain yield and better seed quality (higher bushel weights) in non-traditional wheat-growing areas of Kenya.
The benefit of fertilizer is not always apparent. Fertilizer may increase the disease incidence and competition of weeds, such as wild oats. High N levels may promote vegetative growth, delayed maturity, predispose the crop to foliar diseases and lead to severe lodging and reduced yield and seed quality. In Ethiopia, both N and P increased the incidence of stripe rust, though the effect of P was less pronounced (Tanner et al., 1992). In a similar study, the density of wild oat panicles increased with N fertilizer, but decreased with P fertilizer. Top dressing wheat crops with high levels of N will make the crop lodge, which makes it difficult to be field inspected by the seed certification service.
Cleanliness of machinery
Cleanliness of machinery upon planting is very important. Seed drills should be cleaned with compressed air when changing between varieties and other crops of similar seed characteristics. Vans and trailers used for transporting the seed should be completely clean to avoid contamination.
Isolation
Isolation, growing a seed crop separate from all sources of contamination (genetic, physical and pathological), is one of the fundamental seed production techniques. In practice, such contamination can be reduced by not planting a seed crop in the vicinity of a similar crop that may contaminate it. Small, long and narrow fields need larger isolation distances than large or wide fields.
Long and narrow strips are more prone to contamination than square fields. The minimum distance required for a particular crop is usually prescribed by the national seed regulations and depends on the seed class. Minimum isolation distances are larger for the early than for the later generations.
Wheat is entirely a self-pollinating crop with a very low percentage of crosspollination, from 1 to 4 percent (Doerfler, 1976). Therefore, the risk from genetic contamination through out-crossing is small. Appropriate isolation is, however, required to minimize physical contamination.
For wheat, it is usually sufficient to have a small strip of land between different fields to avoid mechanical admixtures. Minimum isolation distances (in meters) used in some Middle Eastern and North African countries are presented in. In India, an isolation distance of at least 3 m is required to separate a wheat seed field from the same variety not conforming to the standard (Randhawa, 1983).
Early generations, such as breeder seed, can be located in the middle of a field with the same variety, which is a common practice in some North African countries. Breeder seed (G1) grown in the middle of a pre-basic (G2) field and G2 in the middle of a basic (G3) field (Plate 75) of the same variety to reduce risk of genetic and mechanical contamination .For wheat, isolation distances are more important when dealing with smut-susceptible varieties. In India, Agarwal (1983) reported that basic and certified seed fields of susceptible wheat varieties should be isolated by 150 m from fields infected with loose smut in excess of 0.1 and 0.5 percent, respectively.
In Morocco, a 150 m isolation distance is required from other wheat fields if infection with loose smut is beyond 0.1 percent for pre-basic, 0.2 percent for basic, 0.3 percent for certified 1st generation and 0.5 percent for certified 2nd generation seed (WANA Secretariat, 1995). Restricting the number of varieties grown for seed multiplication per farm will reduce the chances of contamination. For example, in Tunisia only one wheat variety can be multiplied on a farm.
Crop management
Agronomic management should be optimal and is similar to that for a grain crop. Small differences do, however, exist: using lower seed rates to increase the multiplication factor; leaving lanes to facilitate roguing and inspection; applying slightly less than optimum amount of N to reduce lodging; maintaining the species and variety purity; controlling diseases that are seed transmitted.
Roguing
Roguing, removing undesirable plants, is another fundamental aspect of seed production. Undesirable plants, commonly known as rogues, are: (i) off-types or genetic variants of the same variety; (ii) other varieties of the same species; (iii) other crop species of similar growth habit and seed characteristics; (iv) noxious weeds; and (v) infected plants with seed-borne diseases. Roguing is carried out to maintain the variety and species purity of the crop and to keep the seed crop free from seed-transmitted diseases.
Roguing follows a systematic procedure and should be carried out at the time when rogues can be most easily identified and before any contamination occurs to the seed crop. The best periods for roguing a wheat seed crop are at heading and at maturity because off-types and other varieties of the same species are most easily identified. In wheat, all off-types, including those that appear due to residual segregation, should be removed. For example, the inherent problem of tall off-types in semidwarf wheat varieties due to aneuploidy, arising from chromosome pairing failures at meiosis, has been discussed by Storlie and Talbert (1993) and Worland and Law (1985). Similarly, other crop species whose seed is difficult to separate during processing (barley, oats, triticale, rye), noxious weeds (wild oats, lolium) and infected plants with seed-borne diseases (i.e. Fusarium, Helminthosporium, Tilletia) are usually easily distinguished at these stages. It may be necessary to rogue the field several times, and all tillers and roots should be removed (pulled) to prevent regrowth. Rogues should be removed from the field and disposed of far away from the field or burned.
Roguing loose smut (Ustilago tritici) infected plants has no effect (except in reducing the disease inoculum) because the spores have already been spread and infection of the seed crop has taken place by the time the symptoms become visible. Therefore, certification schemes often do not allow the removal of smut-infected plants. However, reports from India indicated that loose smut-infected plants do head earlier and that flag leaves of smutted tillers exhibit yellow chlorotic streaks, yellow patches or yellowing at tips, even before ear emergence, and can thus be rogued before flowering. However, plants without streaks were also smutted (Agrawal and Gupta, 1989).
Seed certification schemes set minimum standards for each class of contaminants that are permitted in a seed crop. Roguing aims at ensuring that these standards are met. Roguing should be carried out only when the seed fields do not meet these standards; roguing fields that meet the standards is not economical.
While roguing, no selection should be carried out to ensure that the genetic make-up of the variety remains the same. Therefore, roguing of early generations should preferably be carried out by the breeder or under the breeder's supervision. Roguing in early generations can be most effective.
Field Inspection:
Ø The best time to access cultivar purity is after ear-emergence when seed has started to fill.
Ø Latter inspection when glume and seed colour can be observed.
Irrigation:
Depending on the soil, four to six irrigations may suffice. The first irrigation should be given at crown root initiation stage, about 30 to 35 days after sowing. Other irrigations should be given at late tillering, late jointing, flowering, milk and dough stages. Two to three extra irrigations may be needed on light soils. Critical phases for irrigation are:
First : Crown root initiation ( 30-35 DAS)
Second most critical stage – Flowering
Third important stage – jointing and milk stages
For varying number irrigations
No of irrigations | Stages |
1 | CRI |
2 | CRI + LJ |
3 | CRI + B + M |
4 | CRI + LT + F + M |
5 | CRI + LT + LJ + F + M |
6 | CRI + LT + LJ + F + M + D |
CRI – Crown root initiation; LT – Late tillering; LJ – late jointing; F- Flowering; M- milking; D – Dough stages
Interculture:
Timely weeding and interculture are essential. Periodic hoeing and weeding keep the field free of weeds. For control of broad-leaved weeds spray 2-4 D at therate of 0.5kg active ingredient per hectare in 750 litres ofwater after 25 to 30 days of sowing. for control of Phalaris minor or wild oats make a pre-emergence application of pendamethalin (stomp) @ 1 kg ai per ha in 750 litres of water or spray Isproturon @ 1 kg ai per ha in 750 litres of water after 35 days ofsowing.
Diseases of Wheat
The major diseases of wheat in India are three rusts - leaf, yellow and stem rust, Karnal bunt, foliar blights, powdery mildew and loose smut. Diseases of limited importance include head scab, foot rot and flag smut; these diseases though of lesser importance, may be important in certain pockets.
1-Leaf Rust /Brown Rust (Puccinia recondita tritici)
Distribution: Throughout wheat growing regions of India.
Development: Pathogen over-summers in low and mid altitudes of Himalayas and Nilgiris. Primary infections develop from wind deposited urediospores in eastern Indo-gangetic plains in middle of January where it multiplies and moves westwards by March. Temperatures of 20 ± 5°C with free moisture (rain or dew) cause epidemics. Severe infection causes upto 30 percent yield losses.
Management: The presently recommended varieties in most of the wheat growing zones are rust resistant.
2-Stripe Rust /Yellow Rust (Puccinia striiformis tritici)
Distribution: Hills, foothills and plains of north western India and southern hills zone (Nilgiri hills of Tamilnadu).
Development: Spreads through air-borne urediospores , when temperature are 10-20°C but the spread is checked above 25°c. Pathogen survives in the cool temperatures of hills (Himalayas and Nilgiris) and the primary infection takes places by middle of January in the foot hills and sub mountainous parts of north western India. Also, infection comes from across the western border, hence the probability of evolution of new races increases in this area. Yellow rust from Nilgiri hills cannot come out of the zone due to high temperatures in the Peninsular and Central India.
Management: Most of the presently recommended varieties are resistant. Major emphasis is on host resistance and cultivation of resistant varieties is the main strategy of management.
3- Stem Rust /Black Rust (Puccinia graminis tritici)
Distribution: Mainly in Peninsular and I Central India, may occur in traces in Northern India.
Development: Develops from air-borne urediospores, needs free moisture and temperature above 20° C for spread. It can cause severe grain losses if infection is early. The pathogen perpetuates in Nilgiri hills during off season and becomes airborne. If Peninsular and Central India experience rainfall during November then epidemics are severe. Late infections cause less damage in north India.
Management: The presently recommended varieties in most of the wheat growing zones are rust resistant, hence the old susceptible varieties be avoided.
4- Karnal Bunt (Tilletia indica or Neovossia indica)
Distribution: Parts of Northern Plains, especially Punjab, parts of northern Haryana, foot hills of J&K and HP., tarai area of Uttranchal, in lesser severity in Rajasthan, Bihar and UP. The states of Gujarat, Maharashtra, Karnataka and several parts of M.P. are free of KB.
Development: Seed and soil-borne; infection occurs at flowering by means of soil-borne inoculum. The degree of disease development depends upon the weather conditions prevailing during spike emergence to grain filling stage of crop. If the rains occur during the month of February in north Indian plains (disease - prone areas), the disease is likely to come with higher severity.
Management: Among the present day varieties, PBW 502 is resistant while the others show various levels of susceptibility. For management of this disease, one spray of Propiconazole (Tilt 25EC@ 0.1 %) should be given at the time of anthesis. Integration of one spray of propiconazole with one spray of bioagent fungus, Trichoderma viride (0.4% suspension) gives almost cent per cent disease control. The bioagent spray should be done before earhead emergence (Crop growth stage 31- 39 on Zadoks scale), followed by the spray of chemical at start of earhead emergence (crop growth stage 41 -49 on Zadoks scale). Two sprays of T. viride, at these two critical growth stages also give non chemical control of the disease which is almost similar to one spray of propiconazole. Chemical control should be adopted mostly in seed production plots.
5- Black Point (Alternaria alternate)
Development: Disease causes blackening of embryonic region of the seed (black point), discoloration of area beyond the embryonic region (black discoloration (Caused by Aalternata, Curvularia lunate, Epicoccum sp., Bipolaris sorokiniana, etc.) and eye-spot symptom (B. sorokiniana). The warm and humid weather at grain filling or near maturity favors this disease.
Management: This disease is of minor importance. Only when the disease percentage is high, it causes concern to the trader and the consumer. The discolored seeds are mostly shrivelled and they are separated out during processing.
6- Loose Smut (Ustilago segatum / U. tritici)
Distribution: North Indian plains and northern hills zone.
Development: It is a seed borne disease; infection occurs during Loose Smut flowering through wind-borne spores. The infection remains dormant inside the otherwise healthy looking seed but the plants grown from such seeds bear infected inflorescence. Infection is favored by cool, humid conditions during flowering period of the host plant.
Management: Disease can be easily controlled through seed treatment with systemic fungicides hence resistance breeding has not attracted much attention. Treat the seed with fungicides like carboxin (Vitavax 75WP @ 2.5g / kg seed), carbendazim (Bavistin 50WP @ 2.5g / kg seed), tebuconazole (Raxil 2DS @ 1.25g / kg seed) if the disease level in the seed lot is high. If it is low to moderate, treat the seed with a combination of Trichoderma viride (@4 g/ kg seed) and half the recommended dose of carboxin (Vitavax 75WP @ 1.25g / kg seed).
7- Foliar Blights
(Bipolaris sorokiniana (Spot blotch), Pyrenophora tritici repentis (leaf blotch or tan spot), Alternaria triticina (Alternaria leaf blight)
Distribution: Mainly in eastern India but also occurs in Peninsular and Central Foliar blights India. This disease complex is emerging as a problem in the north western India too.
Development: The disease requires high temperature and high humidity. This disease is more severe in late sown crop and causes substantial yield losses through formation of shrivelled grains. Most of the varieties are susceptible or moderately susceptible. The disease can be controlled through one spray of propiconazole (Tilt 25EC @ 0.1 %).
8- Powdery Mildew (Erysiphe graminis tritici)
Distribution: Mainly in the cooler areas and hilly region; foot hills and plains of north - western India and the southern hills (Nilgiris).
Development: Powdery mildew can easily be diagnosed by the white, powdery patches that form on the upper surface of leaves and stem. With age, the patches turn dull dirty white and may have small black specks embedded. This disease can spread to all aboveground
parts of the plant, including earhead and awns. The disease infects plants during periods of high humidity (not necessarily rain) and cool to moderate temperatures. Low light intensity, which accompanies dry weather and a dense crop canopy favours this disease.
Management: Present day varieties are not resistant to powdery mildew. Hence, the disease severity is more in some pockets. Avoid excessively dense, stands by using adequate seed. For chemical control, one spray of propi-conazole (Tilt 25EC@ 0.1 %) on disease appearance (which usually occurs during early March in northern plains) is highly effective.
9- Head Scab (Fusarium graminearum)
Distribution: Parts of Punjab, especially in the sub mountainous regions. Bread wheat suffers lesser damage than the durum. It was first recorded in severe proportion in some parts of Punjab during 1995-96 crop seasons and again during 2004-05 crop seasons.
Development: Disease development is favoured by cool, moist weather with high humidity. Spores are produced on crop debris and reach the leaves through rain splash or wind. Apart from ear head infection, it can cause seedling blight and foot rot leading to lodging. In severe cases, it can cause shriveling of grains and low-test weights. At present, it is a disease of limited importance but has the potential to emerge as a major problem due to the production of toxins.
Management: Bread wheat is more resistant than durum. However, no resistant varieties are available. Hence, vigil is needed for this disease.
Wheat Insect Control Recommendations
Aphids: Several aphids feed on the leaves and grain heads of wheat. These pests are signifcant in that they are capable of transmitting diseases to the plant such as barley yellow dwarf virus in addition to the damage inficted by their feeding habits. Adult aphids are only about 1/8 inch long, and adults may or may not have two pair of nearly transparent wings.
Oat-Bird Cherry Aphid is dark green in color and is responsible for transmission of the barley yellow dwarf virus. This is usually the most common aphid observed in wheat. Corn Leaf Aphid is bluish-green and all of the legs, cornicles and antennae are black. Greenbug is a pale green, usually having a dark green stripe down the back of the wingless forms. The tips of the legs and cornicles are black, and the antennae are mostly black. Rice Root Aphid occurs on the roots of wheat and has been known to transmit barley yellow dwarf virus.
Armyworms: Armyworms can be serious pests of wheat when populations reach large numbers. Armyworms get their name from their migrating habit, as they sometimes start at one portion of the feld and devour everything in their path.
True Armyworm: Damaging infestations of true armyworm normally occur in the spring. Mature larvae are smooth, almost without any hairs, greenish-brown to reddish-brown, with a dark stripe along each side. A broad dorsal stripe runs down the length of the back. This species differs from the fall armyworm by having a dark lateral band on the outer portion of each proleg. Besides feeding on foliage, larvae will sometime cut the heads of maturing wheat plants.
Fall Armyworm: As the name implies, the fall armyworm is normally a pest of early planted seedling wheat. These insects can completely defoliate a wheat feld when populations are very large. This insect differs from the true armyworm by having a prominent inverted Y on the front of the head and no dark bands on the outer portion of the prolegs.
Hessian Fly: These small insects have been responsible for tremendous wheat losses in the past. Hessian fy larvae feed on stems at the base of plants, hidden behind the leaf sheaths. Larvae are reddish at frst emergence and turn white or greenish white; they are shiny and without legs. Larvae are legless, resembling small grains of rice, and our approximately ¼ inch long when full grown. The pupae, or fax seed stage, are brown in color but otherwise similar to the larvae. Tennessee typically does not have signifcant problems with this pest. However, early planted wheat is susceptible to infestation. Planting after October 15 (i.e., the “fy free date”) will greatly reduce the likelihood of serious Hessian fy infestations. Also, avoid planting wheat as a cover crop prior to the fy free date. Volunteer wheat is a good fall host for this pest, and any volunteer wheat should be destroyed before September. Plowing under wheat stubble after harvest may help reduce subsequent infestations in the fall. Although some varieties are available with resistance to Hessian fies, there are no varieties with adequate resistance to the fy biotype most common in Tennessee (Biotype L).
Cereal Leaf Beetle: The cereal leaf beetle is a pest of wheat, oats, barley and other cereal crops. It has been found in most all counties in Tennessee, and may be present from April - June The larvae are pale yellow and soft-bodied, but the larvae are normally covered with their fecal material giving them a dark gooey, shiny appearance. Adults are shiny, black beetles with red legs and thorax and are approximately 3/16 inch long. Adults and larvae skeletonize the leaf tissue between the veins.
Greenbug: This aphid injects a toxin while feeding. Treatment should be made when aphids are killing three or more leaves per plant. For wheat less than 6 inches tall, treatment should also be considered if greenbugs number 50 or more per linear foot. Treatment should also be made if greenbugs number 200 or more per foot in wheat 6-10 inches tall.
Armyworms: Treatment for fall armyworm should be considered when four or more larvae are present per square foot (16 per 4 square feet). For true armyworm, use a threshold of 6-8 larvae per square foot if wheat is still in the milk stage. Once past the milk stage, wheat can tolerate higher populations and treatment is not usually recommended unless larvae are cutting wheat heads.
Hessian Fly: Foliar applied insecticide are diffcult to time and only marginally effective. Plant after the fy fee date (October 15) and use resistant varieties if they are available. Resistant varieties may help suppress Hessian fy populations, although no varieties provide adequate resistance to Biotype L. Insecticide seed treatments (e.g., Cruiser and Gaucho) will provide some suppression of fall infestations of Hessian fy.
Cereal Leaf Beetle – Check 10 plants per sample site for larvae and adults. Treatment is necessary if one larva and/or adult is present per stem.
HARVESTING
Mechanical harvesting is a common practice for seed production fields. Breeder and pre-basic seed are harvested by plot combine and do not constitute many problems. Basic and certified seed, however, have to be harvested with commercial combine harvesters.
The most critical factors to be considered are seed moisture content, mechanical damage and cleanliness of equipment. For seed crops, dry weather during ripening and harvesting is essential.
Moisture
Cereal seed reaches physiological maturity between 35 to 45 percent moisture content, but it needs to dry down to a safer moisture content for harvesting and storage (Boyd et al., 1975). The seed moisture content can be used as an indicator of when the crop is ready for harvest. Electric moisture meters or the crop characteristics can be used to decide when to harvest. For wheat, threshing or combine harvesting at 16 to 19 percent moisture content reduces mechanical damage (Thompson, 1979).
Mechanical damage
Proper adjustment of the concave clearance and drum speed of a combine is essential to avoid damage to the seed crop. Mechanical damage becomes a serious problem for durum wheat seed production in Algeria (Lakhdar et al., 1998) and Morocco (Grass and Tourkmani, 1999). In Algeria, seed harvested by a single ear thresher or combine showed low germination and increased fungal attack (Lakhdar et al., 1998).
Cleanliness
Combine harvesters are often difficult to clean and may still harbor contaminating seed even after thorough cleaning. The availability of compressed air is important. The combine should be thoroughly cleaned before harvesting, as well as between different varieties. When harvesting the next variety, the first few hundred kilograms of seed may be discarded because contamination may still be present in the combine. For larger plots of certified seed, it is also possible to harvest and discard the outlying rows of the field.
After harvesting, the seed should be packaged in new and clean bags to avoid contamination.
PROCESSING
After a seed crop has been harvested, the seed, if necessary, has to be dried and cleaned, i.e. removal of inert matter, seed of weeds, other crops and other varieties, and seeds that are diseased, damaged and deteriorated. Cleaning can be done because wheat seeds differ in length, width, thickness, density, weigh and shape.
For wheat seed cleaning, mainly screens, indented cylinders and air are used.
Screens separate based on the width and thickness; a width (or diameter) separation is obtained by round screens, while for thickness separation oblong screens are used (Plate 76). Indented cylinders carry out length separation; the indents (cells or pockets) in the cylinder will, depending on their size, lift the seeds, which fit in the indents. Air separates seeds according to their behavior in an air stream. The most important characteristic is the weight; light particles (dust, chaff, glumes or empty or partly filled seeds) will be lifted, whereas the heavier seed will fall down through the air stream. Each crop requires a different set of machines.
The raw (unprocessed) wheat seed is received from growers in bags or bulk and sampled to evaluate the need for fumigation, drying and cleaning, as well as to guide and monitor processing operations. If seed moisture is too high, the seed is first (pre-cleaned and) dried. If insects are present, the seed should be fumigated. After the raw seed has been received and where necessary fumigated, processing operations will be followed as below:
Pre-cleaner: Wheat seed often contains considerable plant material trash, and it is often pre-cleaned. A typical pre-cleaner is similar to an air-screen cleaner, except that it has only one air channel to remove light material, one top scalping screen to remove large particles and one bottom grading screen to remove small particles.
Dryer: If wheat seed is above 11 to 12 percent moisture, it is dried before it goes into bulk storage or processing.
Air-screen cleaner: This is the basic cleaner, usually with two air channels and, preferably, four screens. The first air channel (head aspiration) removes dust and light materials as the seed falls from the feed hopper. The second air channel (tail aspiration) removes light seed and materials after the seed passes through the last screen. Although screen configurations vary considerably, one or two top or scalping screens remove particles larger than the good seed, and one or two bottom or grading screens remove particles smaller than the good seed. Because the average size of wheat seed varies according to the growing conditions, standard screen sizes cannot be recommended. Hand testing screens should be used to determine the exact screen perforations.
Length separator : A length separator is almost always used to clean wheat seed. By using the proper machine configuration, shorter or longer undesirable materials (such as broken grains, weed seeds, oat, barley, etc.) are removed. Broken grains and weed seeds, which are shorter than the good seed, are removed by using cylinders with smaller indents. Larger impurities can be removed by using a cylinder with indents that lift all good seed, but contaminants (wild oats, oats or barley grains and unthreshed glumes) remain in the cylinder.
Gravity separator: After the seed is cleaned by the air-screen cleaner and indented cylinder, it may be necessary to use a gravity separator. The gravity separator classifies a seed mixture mainly according to density or specific gravity. It can be used to remove unthreshed glumes and soil particles, which have similar sizes to wheat but different weights. Another application is the removal of weevil-infested grains from the seed lot and upgrading seed (in order to improve germination). Furthermore, wild oats and some barley may be removed from the wheat seed lots, but at the expense of substantial amounts of good seed and only after recycling the material a number of times on the gravity separator.
Treater :Wheat seed should, if necessary, be treated with the appropriate fungicide to protect the seed and seedling after planting. Insecticides are sometimes applied to protect seed in storage and in the soil. Treatments may be applied to protect the seedlings or adult plants against pathogens carried on or in the seed.
Dryer : In humid and hot climates, seeds may be sealed in vapourtight plastic bags to maintain viability over longer periods. In such cases, wheat seed moisture content must be below 9 percent, preferably not over 8.5 percent. Usually, a dehumidified, closed-circuit dryer is used after the seed treatment is applied.
Bagger-weigher: The final step is to weigh the proper amount of seed into the proper kind of bag. Wheat seed bags should be of a size that fits local farmer needs (seed rates and field size).
During processing, strict attention should be paid to the cleanliness of the processing machines and any admixture should be avoided. Every processing plant should have a complete set of hand screens, a small air-screen cleaner and an indented cylinder to help determine the proper processing requirements. It is also essential to have an internal quality control laboratory attached to each seed plant with a small seed testing facility. This laboratory unit should constantly monitor the quality of the seed and the efficiency of processing operations.
Seed yield: The average seed yield varies from 3000 to 4000 kg/ ha
SEED TREATMENT
Seed health is an important attribute of quality, and seed used for planting should be free from pests. Seed infection may lead to low germination, reduced field establishment, severe yield loss or a total crop failure. For example, severely infected wheat grains with Karnal bunt either fail to germinate or produce a greater percentage of abnormal seedlings (Singh and Krishna, 1982; Singh, 1980). In wheat, fungi (Fusarium spp., Tilletia spp., Drechslera spp., Septoria spp.and Ustilago spp.), bacteria (Corynebacterium, Pseudomonas and Xanthomonas) and nematodes (Anguina tritici) are the most important seed-borne diseases due to their worldwide distribution and losses they incur in crop production (Mamluk and van Leur, 1986; Diekmann, 1996a).
Chemical seed treatment is one of the efficient and economic plant protection practices and can be used to control both external and internal seed infection.
It protects young seedlings or adult plants against attack from seed-borne, soil-borne or airborne pests. It disinfects seed from pathogen, checks spread of harmful organisms, promotes seedling establishment, maintains and improves seed quality or minimizes yield losses. Selection of the proper chemical depends on the target organisms. A wide range of chemicals (Diekmann, 1993) and equipment (Jeffs and Tuppen, 1986) are now available for such purposes. Some recent literature gives detailed information on the management of bunts and smuts
(Wilcoxson and Saari, 1996) and bacterial (Duveiller et al.,1997) seed-borne diseases of wheat.
Meisner et al. (1994) indicated that Vitavax 200 (Carboxin [37.5 percent] and Thiram [37.5 percent]) is an effective broad spectrum seed treatment fungicide, both for externally and internally seed-borne diseases of wheat. Moreover, pre-harvest foliar application of chemicals can also reduce the internally seed-borne fungi and can be combined with seed treatment to produce healthy seed. Sinclair (1983) cited that foliar spraying of wheat with benomyl, methyl benzimidazole carbamate or benomyl plus mancozeb reduced F. graminearum, whereas capatafol and mancozeb reduced S. nodorum.
Apart from disease control, seed treatment also has a positive effect on crop growth and yield. Ahmed (1996) reported that wheat seed treatment with systemic fungicides, such as Baytan, Raxil and Vitavax, significantly increased crop stand, grain yield and yield attributes. Meisner et al. (1994) reported a 10 percent increase in wheat yield due to seed treatment with Vitavax 200 against smuts.
Seed production in disease-free areas or under effective disease control and field inspection schemes is very important to obtain disease-free seed. Thus, understanding disease epidemiology, its transmission rate and economic threshold, combined with seed health testing, could help to define the need for seed treatment.
STORAGE
Seed is 'in storage' from the time it reaches physiological maturity on the parent plant until it is planted by the farmer. Germination is highest at physiological maturity, and viability then declines inexorably until the seed dies. Deterioration of seed viability cannot be reversed once it has occurred.
Good storage cannot improve the quality of poor seed; therefore, only seed with high germination and high vigour should be put into storage. Storage conditions should then be as favourable as possible to maintain quality. Unfavourable conditions at any time during storage may reduce or destroy viability.
Seed should be harvested when it reaches harvest maturity, dried to a safe moisture content (if necessary), stored under favourable conditions and protected from damage and pests until it can be planted. Conditions that cause the loss of seed viability in storage, include: immature or damaged seed cannot survive long storage periods. Seed should be harvested when properly matured; mechanical injury to seed during harvest or handling makes it more susceptible to deterioration in storage; seed should be properly dried before going into storage and protected from moisture and high relative humidity. Fungi (Aspergillus and Penicillium) cause damage to stored seed if seed moisture is high; high storage temperature has a damaging effect on seed. Stores should be designed so that low temperatures are maintained; some seed treatments cause
seed to die if it is stored too long; therefore, seed should only be treated when it is certain that it will be sold for planting; rodents, mainly rats and mice, can be most destructive to seed. Effective rodent control (traps and poison) is essential in all seed stores. A complete programme of exclusion, sanitation and control should be used; insects should be controlled by a combination of insecticides and fumigants.
Use safest fumigants (e.g. phostoxin) because some fumigants (e.g. methyl bromide) will reduce germination.
Keeping the seed as dry and cool as possible in clean stores is the best management practice. If seed is dry and cool, physiological processes, fungal activity and insect activity are low. Select a seed storage site that is cool and dry (low relative humidity). O'Dowd and Dobie (1983) described the design of open seed stores, and Ellis (1988) suggested a practical guideline in choosing alternative sites for short- and medium-term seed storage.
Clements (1987) discussed the problem associated with wheat storage under tropical conditions. Wheat seed is storable for medium to long periods if kept under safe storage conditions. For wheat, high seed moisture (above 11 to 12 percent) is the most damaging, and seed must be kept as dry as possible in storage. The response of wheat seed to high atmospheric humidity (RH) in storage varies with temperature. Clements (1987) reported that at 25°C and 75 percent RH the equilibrium moisture content for wheat is 15 percent, and at 90 percent RH this may increase to 19.7%. He also stated that the critical moisture content for wheat that increases the rate of respiration is 14.6 percent. In general, stored wheat seed should be kept at moisture content levels below 12 percent and relative humidity should not exceed 50 to 60 percent. Diekmann (1996b) indicates that in cereals there are more than 20 different species of storage pests of which grain borer (Rhyzopertha) and weevils (Sitophilus) occur most frequently. Some insects, such as the khapra beetle (Trogoderma granarium), are quarantine pests in some countries. In India, it is reported that the rice weevil (S. oryzae), lesser grain borer (R. dominica), khapra beetle and flour beetle (Tribolium castaneum) are important seed storage pests of wheat (Singh, 1985). In Bangladesh, farmers traditionally use natural insecticides, such as neem (Azadirachta indica), biskatali (Rumex obtusifolius) and tobacco leaves, as insect repellents for farm-saved seed (Ahmed, 1985).
Management of storage Pest
The management of stored wheat pests should be done in a sequential and integrated manner. An effective pest control system involves
• Harvesting, drying and storage of clean dry wheat
• Disinfecting the storage system and
• Controlling or preventing pest infestation during the storage period.
Harvesting, drying and storage
Seed grain should be dried to12% moisture before storage. Wheat seed needs to be harvested and dried so that it will not cause cracking of the seed , as cracked grains are easier for insects to infest.New seed should not be stored near older seed unless all insects have been eliminated from the older seed.
Disinfesting the storage system
Disinfestations require a systematic and thorough cleaning of all sources of infestation before storage. Old seed residues in the storehouses, seed bins, harvesting and threshing equipment should be treated, removed or destroyed.
Storage containers, structures and equipment can be treated with:
Malathion (50EC) at 5ml/20l of water @20ml/m2
Fenitrothion (50EC) at 5ml/l water @20ml/m2
Deltamethrin (2.5% WP) at 1.5g/l water @20ml/m2
Fenitrothion (50EC) at 5ml/l water @20ml/m2
Deltamethrin (2.5% WP) at 1.5g/l water @20ml/m2
If thorough cleaning of containers is not possible, the containers may need to be sealed and fumigated with phosphine. All second hand bags should be examined and where necessary treated with either a fumigant, insecticide or dipped in boiling water. Solutions of Malathion (50EC) and Fenitrothion (50EC) at 5ml/20l of water and Deltamethrin (2.5% WP) at 1.5g/l water @20ml/m2 can be used for dipping the bags.
Controlling infestations within the seed
The first step in controlling any infestation is to determine the level of infestation and then select an appropriate method for control. All storage should be checked, preferably every fortnight, and at least monthly. Random samples need to taken from all seeds and tested for infestation. If there are more than 4 insects per kg some form of treatment is required.
Spraying insecticides
Spraying of BHC wettable power, pyrethsum and malathion at 3 weeks interval can be done as a prophylactic treatment of the surface area of the store house. The dosage recommended is as follows.
BHC WP (50%) 31/100m2 area in 1:25 dilution
Pyrethsum (2.5 EC) 31/100 m2 area in 1:300 dilution
Malathion (50 EC) 31/100m2 area in 1:300 dilution
seed treatments
Malathion is a widely used chemical and is toxic to insects if it comes into direct contact with the pest. Malathion is considered one of the safest organophosphate insecticides as it is not highly toxic to humans or pets, and breaks down fast under tropical conditions.
Fumigation
Fumigants are effective against storage pests because as gases they can reach the pests in the most remote hiding place. The range of safe fumigant chemicals that can be used is now restricted to phosphine and carbon dioxide.
Phosphine fumigation
Phosphine fumigation is undertaken using tablets and pellets. These tablets and pellets release phosphine gas when they come into contact with humid air. Phosphine is toxic to all insects. When insects are exposed to fumigation in a sealed environment all stages of development from the eggs, larvae, pupae to adults are killed.
.Minimum Exposure times at 60% Relative Humidity
Temperature (oC) | Tablets (days) | Pellets (days) |
Under 5 | No fumigation | No fumigation |
5-10 | 10 | 8 |
11-15 | 5 | 4 |
16-25 | 4 | 3 |
Over 25 | 3 | 3 |
Carbon dioxide fumigation
Insects need oxygen for respiration. With carbon dioxide fumigation, much of the oxygen in the storage bin is replaced by carbon dioxide that suffocates, dehydrates and also produces toxic chemicals in the blood of the insects. To be effective, elevated carbon dioxide levels must be maintained until all insects die. The required exposure time depends on the percentage of carbon dioxide and the temperature of the seed. The cost of CO2 fumigation is high.
Guidelines for Carbon Dioxide Application
seed Temperature (oC) | Minimum CO2 Levels (%) | Days for control |
25-30 | 80 | 8.5 |
25-30 | 60 | 11 |
25-30 | 40 | 17 |
25-30 | 20 | Weeks to months |
Physical conditions
Temperature:
The ideal temperature for stored product insect growth is 25-30oC. The lower the seed temperature the slower the insect populations increase. Aerating the seed immediately after harvest so the seed is cooled will significantly reduce insect infestation. At 15oC the insects stop laying eggs and development stops. At lower temperatures insects will die.
High temperatures will also kill all stages of insects (eggs, pupae, larvae and adult) if exposed for a sufficient period of time. The most realistic use of high temperature is at drying or in some instances when the seed is being removed from storage for sale. Generally insects need to be exposed to temperatures of 50-55oC for at least 15 minutes.
Diatomaceous earth
Control of some insects (e.g. rusty grain beetle) can be achieved by using a non-toxic dust made from prehistoric diatoms. When the insect comes in contact with this dust, the waxy covering on the exoskeleton is absorbed, leaving them prone to dehydration and death. The product is applied as the seed is loaded into the bin and is most effective when applied to dry seed at harvest. Control can take up to 5-6 weeks.
Rodents in storage
Rats have been estimated to damage more than 1% of the world cereal crops and, in developing countries, estimates of 3-5% have commonly been reported. There are around 50 diseases which can be transferred to humans by rodents, including typhoid, paratyphoid, and scabies. In addition, rodents may be vectors of a large number of diseases affecting domestic animals. As rodents prefer food rich in proteins and vitamins and feed mainly on the embryo, they cause particular damage to the nutritional value and germination ability of seeds. The three most important rodent species are:
• Black rat or House rat (Rattus rattus)
• Norway rat or Common rat (Rattus norvegicus)
• House mouse (Mus musculus)
There are also a number of species that are of great importance in specific regions:
• Multi-mammate rat (Mastomys natalensis) in Africa and the Middle East;
• Bandicoot rat (Bandicota bengalensis) in Southern and South East Asia;
• Pacific rat (Rattus exulans) in South East Asia, also occurring in Southern Asia
Their teeth characterize rodents. They have a pair of incisor teeth in the upper and lower jaws. The incisors are curved inwards and have an extremely hard anterior coating. The softer inside layer is worn down much more rapidly than the hard, outer layer. This means that the teeth are continually kept sharp, enabling them to damage even materials such as masonry and electric cables. The incisors do not stop growing. This means that the animals are forced to gnaw steadily in order to wear them down. Rats and mice cause losses in a number of ways.
Preventive measures
Good store management and preventive measures taken as part of an integrated control program can help to deal with these factors.
Storage Hygiene and Technical Measures
• Keep the store absolutely clean! Remove any spilt seed immediately as it attracts rodents!
• Store bags in tidy stacks set up on pallets, ensuring that there is a space of Im all round the stack!
• Store any empty or old bags and fumigation sheets on pallets, and if possible in separate stores!
• Keep the store free of rubbish in order not to provide the animals with any places to hide or nest! Bum or bury it!
• Keep the area surrounding the store free of tall weeds so as not to give the animals any cover! They have an aversion to crossing open spaces. Keep the area in the vicinity of the store free of any stagnant water and ensure that rainwater is drained away, as it can be used as source of drinking water.
Keeping Rodents Out
The requirements of preventive rodent control must be taken into account whenever new stores are being built. Particular attention should be paid to doors, ventilation openings, brickwork and the junctions between the roof and the walls. Repair any damage to the store immediately! This applies especially to the doors.
Prescribed Seed standard for seed Certification as per ISTA
Seed Class | Germination % | Moisture | Pure seed (min) | Inert matter % | Other crop seed (max) | Objectionable Weed Seed (max) |
Foundation Seed | 85 | 12.0 | 98 | 2 | 10 | 10 |
Certified Seed | 85 | 12.0 | 98 | 2 | 20 | 20 |
Field Standards
Class of Seed | Off-type | Pollen shading | Objection-able plant | Plant head affected by designated disease |
Foundation Seed | 0.050 | - | 0.010 | 0.10 |
Certified Seed | 0.1 | - | 0.020 | 0.50 |
BY:
Mohammad Safar Alizada Noori
Sr. MSc.(Agri)
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