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

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(Seed Health Management for Better Productivity)1. Determination of true incidence, causes and financial/ personal impact of seed bornediseases.2. Development of more effective methods of salvation and for the testing of seeds (routinemonitoring/epidemiological tools)3. Divestment of better methods for controlling the risks associated with seeds.4. Development of better means of risk assessment including pathogen load andpathogenicity/ toxicity for crops and differential risks among other crops.In order to limit the transmission of the pathogen in to disease free areas, transportation ofinfected/ infested seed from the disease prone areas has been restricted. To meet therequirement, the central seed certification board has formulated strict seed certification standards.To limit the dispersal and build up of Karnal bunt infection, tolerance limits (certification standards),based on visual inspection, are applied to foundation and certified seeds i.e., maximum of 0.05 forfoundation seeds and 0.25 percent for certified seeds. A seed-washing test to quantify the seedborne teliospores for the purpose of seed certification has also been suggested. However, theseed certification standards can be improved by taking account of the total pathogen load on seedlot rather than per cent-wise infection which does not take of a grade of infection. If the teliosporecontamination is beyond 25 spores per grain, the seed lot is rated as contaminated.The seed scientists have developed techniques for analyzing large numbers of samples forseed certification and plant quarantine. The International Seed Testing Association (ISTA) hasimportant roles in defining and promoting standard procedures, and establishing tolerances forseed tests. The advent of newer molecular diagnostics based on nucleic acid and immunologicalreaction permit the sensitive detection of KB. The Pantnagar University took an initiative in 1997 tocombine the know-how so as to formulate standard detection and seed certification methods. Theimmunological formats developed in our laboratory are quite promising not only for the detection ofKarnal bunt infection in seeds but also for use in detection of infestation of KB teliospores. Thesignificance of seed health testing is to ensure the safe movement of germplasms, for the purposeof research and trade. It is also a means of quality control of seedling stocks for crop production.Essential requirements of seed health diagnosticsIn a regulatory climate in which the presence of a single pathogen could lead to regulatoryaction, the need for a reliable method for detecting and identifying the disease entities in grainscan not be overstated. Such a method must meet three requirements: (a) a detection sensitivityapproaching few causative agents; (b) an extraction method that is quick and cost effective in theevaluation of a large number of samples; and (c) compatibility with available biochemical,immunological and molecular methods for identification of pathogenic entities.Molecular diagnostics for diseasesDisease diagnostics and pathogen detection, a primary component of any cropmanagement programme, is also helpful in monitoring sanitary and phyto-sanitary measures to- 180 -
(Seed Health Management for Better Productivity)seed quality. Molecular diagnostics based on immunological and DNA techniques can provide aneasy-art-technology for disease surveillance and disease forecasting. Testing for and monitoring ofpathogens is a component of seed quality control. For current seed health testing, seed-bornepathogens are usually recovered by conventional agar plating, blotter tests or by serologicaltechniques. These traditional methods of detection and identification are often time consuming andlabor intensive. Over the past decade, considerable advancement has taken place in thedevelopment of molecular diagnostics for detection of pathogens in seeds. Potential benefits(rapid, same-day analysis specific and sensitive tests) this new technology offers make itextremely attractive. The recent and rapid pace of developments in molecular biology has providednew opportunities in diagnostic areas.Modern diagnostic methods are based on high affinity biomolecular interaction betweenligand and binder. These include the nucleic acid hybridization (DNA based) and antibody basedtechniques involving complementary interaction of DNA-DNA, DNA-RNA, RNA-RNA and antigen–antibody (Ag–Ab) interactions that have been applied to KB diagnostics and pathogen detection atthe field level.Sample preparation in diagnosticsThe foremost element to be taken into account in the development and application ofanalytical methods in plant diagnostics is the sample preparation. Discussion of some of thesemethods is relevant at this stage because many of them are distinguished by the relative lack ofsample preparation required before the analysis can be performed. However, some methods dorequire the sample preparation for biological amplification. The biological amplification consists ofextraction stage and culture of pathogen on an enriched medium. Table 1 summarizes attributes tobe considered in the primary selection of diagnostic methods for seed borne plant pathogens.Extraction of seed-borne pathogensSeveral methods of seed-borne pathogens isolation are a modification of general seedwash assays and being currently used by most international seed health laboratories, that havebeen improved by the incorporation of suitable detergents commonly used for extracting fungi fromsoil.Detection techniques based on cellular and molecular differencesFor differentiating one from other pathogens many techniques can be employed. Thepresent methods for testing grain for the presence of seed borne pathogens include microscopicanalysis, pathogenicity tests; isozyme analysis that identifies disease causing entities. However,the procedures have many drawbacks as they rely on individual examiners and are highlysubjective in their nature. The techniques include conventional techniques, biophysical, isozymeand DNA based marker and immunological techniques.- 181 -
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Page 219 and 220: potential. An improvement in qualit
Page 221 and 222: 9. Session Arrangement CommitteeDr.
Page 223 and 224: 9. Dr. Pradip Kumar BorahSr. Scient
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Page 227 and 228: ANNEXURE-IVCENTRE OF ADVANCED STUDI
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