Seed Health Management for Better Productivity - Govind Ballabh ...

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(Seed Health Management for Better Productivity)the infectivity of the pathogen in seed). Most seed tests measure the proportion of infected seed.Because low levels of seedborne inoculum can lead to considerable disease, the most sensitivetest should be used to determine the level of seed infection.Fungi may be detected using a standard blotter test or an agar plate test, the latter being the moresensitive. Seed-borne bacteria can also be detected using an agar plate test. Seeds are oftensurface sterilized with Na O Cl before testing to eliminate other saprophytic fungi, although this pretreatment can reduce the percentage recovery of the pathogens where infections are not deepseated. Results of these standard tests indicate the proportion of infected seed they provide noinformation on the amount of inoculum per seed. Where a high percentage of seed is infectedthere is often more inoculum per seed associated with larger infections and deeper penetration.Seed-borne viruses are usually detected using ELISA or PCR tests. It is important that thediagnostic tests are conducted on germinated seed (seedlings) as virus may sometimes infect theseed test a without infect in the embryo or seedling e.g. PSBMV.Survival on seedSeed borne pathogens can often survive for several years in and on seed. Pathogens arenot always carried on the seed coat but can be harboured deep inside seeds. Fungi and bacteriaare mostly located in the seed coat, and embryo infection is uncommon. Infestation levels of mostpathogens decrease rapidly during storage and long-term storage can eliminate some pathogensfrom seed. Unfortunately, there is likely to be a marked reduction in the viability of seed stored fora long period and this may negate any benefits from lowering disease levels in seed. Viruses arenot carried on the seed coat and are only found in the seed embryo or tissues of the seed coat.Infection of seedMost fungal and bacterial diseases are favoured by wet conditions and seed producedunder warm, humid conditions usually becomes heavily infected while seed produced in drierregions is often free of infection. Seed infection levels are determined primarily by weatherconditions between flowering and maturity and warm, humid conditions during this period oftenresult in heavy pod and seed infection. Dry weather between flowering and maturity minimizes podinfection and is essential for the production of pathogen free seed. There is often considerablevariation between genotypes in their resistance to seed infection.Virus infection in seed depends on the amount of spread of virus between plants during thegrowing season, often by aphid vectors, and the genetic susceptibility of the host plant.Important seed borne diseasesVirusesAlfalfa Mosaic Virus (AMV)Plants may develop a bright yellow leaf mottle, tip necrosis, stunting, pod flattening andblackening. Yields are reduced through plant death, the production of small seeds, and seeds withbrown coat discolouration.Cucumber Mosaic Virus (CMV)- 114 -
(Seed Health Management for Better Productivity)Plants may develop leaf chlorosis (yellowing), stunting, distortion or bunchy appearanceand pods may be flattened and turn purple-brown.Pea Seedborne Mosaic Virus (PSBMV)Plants may develop downward rolling of leaf margins and slight clearing of the veins inyoung leaves. Production of small seeds with distinctive brown staining and 'tennis ball' marking iscommon. Seed discolouration can significantly reduce the commercial value of grain.Bean Yellow Mosaic Virus (BYMV)Plant leaves may develop leaf mottle or a distinctive yellow mosaic pattern, stunting andreduced leaf size. Early infections can seriously reduce plant growth and grain yield.BacteriaBacterial blight (Pseudomonas syringae pv pisi and Pseudomonas syringae pv syringae)Important seed borne disease of field peas. Both these pathogens may be carried by theseed either internally or externally. Water-soaked leaf, stem and pod lesions may occur at anygrowth stage. Yields are reduced through plant death, crop damage and the production of smallseeds. Brown discolouration of the seed coat can sometimes occur.FungiGrey mould and chocolate spot (Botrytis cinerea and Botrytis fabae)Stem infection can cause the damping-off of young seedlings. Later infection causes grey mouldor chocolate spot on foliage and flowers. Yields are reduced through plant death, crop damageand flower abortion. Infected seed can be small and badly discoloured.Ascochyta blight (Ascochyta fabae, Ascochyta lentis, Ascochyta pisi, Ascochyta rabiei,Mycosphaerella pinodes Phoma pinodella)Tan coloured lesions form on leaves, stems and pods. Infected leaves may dropprematurely. Yields are reduced through plant death and crop damage. Infected seed can beshriveled or badly stained.Lupin anthracnose (Colletotrichum lupini)Bending and twisting of stems with a lesion in the crook of the bend. Stem infection oftenresults in the death of plants and major yield losses. Affects both narrow leaf lupins and albuslupins.Phomopsis stem blight (Phomopsis leptostromiformis)Causes yellow-brown lesions on leaves stems and pods. Severe infection can kill plants.Infected seed can be covered with a web-like grey mould. Toxin produced by infected stubble cankill animals.Brown leaf spot (Plieochaeta setosa)Can cause both root rot and leaf spotting. Affected roots develop large dark brown lesions.Irregularly shaped dark brown lesions develop on infected leaves. Can seriously reduce plantgrowth and grain yield.REFERENCES- 115 -
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potential. An improvement in qualit
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9. Session Arrangement CommitteeDr.
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9. Dr. Pradip Kumar BorahSr. Scient
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TRAININGONANNEXURE-IIISEED HEALTH M
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ANNEXURE-IVCENTRE OF ADVANCED STUDI
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SundayApril 6MondayApril 7TuesdayAp
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TuesdayApril 15WednesdayApril 16Thu
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