Induction of Downy Mildew Disease Resistance in Pearl Millet Using Abiotic and Biotic Inducers and the Mechanism of Resistance

Shetty, H.S. (2004) Induction of Downy Mildew Disease Resistance in Pearl Millet Using Abiotic and Biotic Inducers and the Mechanism of Resistance. In: Tiszántúli Plant Protection Forum, 20-21October 2004, Debrecen, Hungary.

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The phenomenon of induced resistance has been variously described as systemic acquired resistance (SAR) and induced systemic resistance (ISR), the term 'systemic' stressing the point that protection is not confined to treated plant parts but extends into non-treated, and often even newly developing parts. Although in the past, propositions were made for an all-compassing term, both SAR and ISR are being used, often depending upon the inducer. In this present paper the differences and similarities and the most distinctive markers of both have been established. Both classes of inducers like biotic plant growth promoting rhizobacteria and abiotic inducer Benzothiodiazole were evaluated for their ability to induce resistance against pearl millet downy mildew disease. Comparative analysis of the nature of resistance induction as well as the underlying biochemical and molecular level was analyzed for both biotic and abiotic induers. Cultures of PGPR Bacillus pumilus INR 7 and BTH were evaluated for their ability to induce resistance against pearl millet downy mildew. Eubiotic preparations of INR 7 and BTH exhibited protective effect (57 and 78%, resp.) against downy mildew disease under greenhouse conditions. These strains pressure expressed protection over 70% in the field under high inoculum pressure. In both cases the time gap required for the building up of resistance was found to be 3 days, whilst the nature of induced resistance was systemic and durable. Histological studies of plants with induced resistance revealed accumulation of lignin, callose and hydrogen peroxide initiated by both biotic and abiotic inducers, however the development of hypersensitive response was noticed only in the case of abiotic inducers. Immunolocalization studies recorded enhanced accumulation of glucanase, peroxidase and chitinase with abiotic inducer, whereas there was observed intense accumulation of PAL and PPO with biotic inducer. Defense enzymes like PAL, POX and PPO were enhanced during ISR mediated by biotic inducer whereas enzymes like glucanase, chitinase and peroxidase were prominently expressed during abiotic inducer mediated resistance development. Salicylic acid was found to be the major signal molecule during BTH mediated resistance whereas jasmonic acid was the major signal molecule during Bacillus pumilus mediated resistance. Molecular analysis of induced resistance showed the earlier and enhanced accumulation of transcripts of defense enzymes such as peroxidase, chitinase, catalase, glucanase during BTH induced, resistance, whereas during INR 7 induced resistance there was prominent accumulation of transcripts of phenlyalanine ammonia lyase, polyphenol oxidase and lipoxygenase and chalcone synthase. The most outstanding difference between SAR and ISR was the induction of the PR proteins transcripts. There was no accumulation of transcripts of PR1 and PR5 during biotic inducer mediated resistance whereas these two proteins were prominently induced during abiotic inducer mediated resistance

Item Type: Conference or Workshop Item (Paper)
Author Affiliation: Downy Mildew Research Laboratory, Department of Studies in Applied Botany, Seed Pathology and Biotechnology, University of Mysore, Manasagangotri, Mysore, India
Subjects: Plant Protection
Plant Physiology and Biochemistry > Plant Physiology
Plant Physiology and Biochemistry > Biochemistry
Divisions: Millet
Depositing User: Ms Ishrath Durafsha
Date Deposited: 12 Dec 2013 08:21
Last Modified: 12 Dec 2013 08:21

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