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

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(Seed Health Management for Better Productivity)The effectiveness of this practice often breaks down, however, when seed is held instorage facilities with poor environmental controls.A few examples of management of storage fungi during seed storage are:Soybean oil applied to reduce growth of storage fungi in maize and soybeans(McGree1988).Insect and storage fungi management by mineral oil and soybean oil treatment inbeans ( Hall and Harman 1991)The fungicides thiabendazole and Iprodione supress growth of storage fungi in stored corn( White and Toman 1994).The potential for natural products ( Flabonoids and Isoflabonoids, andtheir derivatives ) to control storage fungi for seed of bean and soybean is demonstrated byWeidenborner et al 1990.b. Seed Health testingSeed health testing is used primarily to manage diseases by inoculum threshold, todetermine the potential effect of seed borne inoculum on stand establishment in the planted field,and to meet the requirements for phytosanitary certification of seed lots to be exported. For seedhealth testing following methods are routinely used:c. Field inspectionIt requires that the seed production field be examined for symptoms of a disease ongrowing plants. The method is based on the assumption that incidence of infection on plants andseed are related. Although there are few diseases where this relationship has been validated,procedure remains the back bone of Phytosanitary certification in many countries.d. Direct seed assaySeed may be examined visually for clear signs or symptoms expressed on the seedsurface.Another approach is to soften seed tissues and then examine the internal tissues of theseed microscopically for mycelium of the pathogen.e. Incubation testIt requires that the seed be subject to conditions that select for and optimizegrowth oftarget pathogen. Assay usually require pretreatment with a chemical to surface disinfest the seeds,followed by incubation on blotters or culture medium under precisely defined environmentalconditions.f. Grow out testSeed are planted in the field or green house in the absence of other inoculum sources.Seedlings are examined for symptoms produced by the seed borne pathogens. The procedurerequires much time, space, , and labour. It also tends to lack sensitivity, but it can predict well theextent of seed transmission of Pathogens in the planted field.g. Serological assaysSerological assays for seed borne pathogens were first reported in 1965 with anagglutination test for Pseudomonas phaseolicola in beans( Guthrie at al 1965)and double diffusionassay for barley stripe mosaic virus ( Hamilton 1965).The introduction of ELISA to plant pathology- 40 -
(Seed Health Management for Better Productivity)in 1976 stimulated rapid advances in the use of serological assays for seed borne pathogens.Withdiagnostic kits now available from the private sector for ELISA and its variants, serology hasbecome cost- effective and practical to detect seed borne pathogens through out the world .However, a well known weakness in serological tests has been the propensity to detectfalse positive caused by the binding of antibodies to epitopes, which may no longer be a propaguleof the pathogen which can be overcome by combining serological assay with a viability test.h. DNA hybridization assayDNA hybridization assay use a DNA probe that is complementary to DNA in the genome ofthe plant pathogen.The probe is applied to a DNA extract from seed and hybrizied materialdetected by dot blot hybridization assay. The technique has successfully used to detectPeronosclerospora sorghi and P. sacchari in corn ( Yao et al 1990) Pseudomonas syringae pv.Phaseolicola in bean seeds .C. THE PLANTED FIELDa. Seedling emergence and establishmentThere are sound epidemiological bases to establish relationship between seed bornepathogens and seed quality and this impress upon the use of seed treatment to improve seedvigor and reduce the seed borne inoculum for better plant stand in field.b. Transmission of seed borne pathogens: transmission of seed borne pathogens by followingfactors:i. Epidemiological factors affecting seed transmission:Seed transmission for some seed borne pathogens is well defined. Few most promisingfungal pathogens such as Ustilago tritici, Neovossia indica,Telletia caries, Peronospora parasiticain rape seed mustard, and many seed borne bacteria and viruses.Physiological factors may affect the capacity of the seeds to transmit pathogens. Fewexamples are:Downy mildew pathogen in maize can be transmitted when seeds are freshlyharvested, but not once the seeds are dried ( Mc Gee 1988.) Arabis mosaic nepovirus istransmitted inefficiently in Nicotiana seed , because the virus reduce seed germinationEnvironmental factors play a major role in the efficiency of seed transmission of plantpathogens.The seed borne inoculum of Alternaria brassicae or A. brassicicola in rape seed mustardreduces with the seed storage and at temperature above 35 0 C the fungus is auto-eliminated intropical conditions. In Cabbage seedling disease caused by Alternaria brassicicola for e..g doesnot occur below 15 0 C in heavily infected seed lots .ii. Inoculum thresholdInoculum threshold have been established on a sound epidimiological basis for only a fewpathogens, including Phoma lingum in Crucifers, Pseudomonas syringae pv. phaseologicola , andlettuce mosaic virus. For many seed borne pathogens, inoculum threshold is determined eitherarbitrarily or by field observation data ( Schaad 1988). To be of value, however the threshold- 41 -
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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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