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Molecular Characterization of Ascochyta Spp. Causing Pea Blight and Evaluation of Resistance

CSK Himachal Pradesh Agricultural University Repository

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Title Molecular Characterization of Ascochyta Spp. Causing Pea Blight and Evaluation of Resistance
 
Creator Kapoor, Vikash
 
Subject 635.656 Peas
 
Description Ascochyta blight was found to occur across Himachal Pradesh (2006-2007) with an average incidence of 15.77 per cent. High disease incidence was observed in district Mandi (33.37%) followed by Chamba (32.88%) and Kinnaur (32.83%). No single criterion was sufficient to distinguish various species of Ascochyta infecting pea but when considered in combination, 36 were designated as A. pinodes; two as A. pinodella and one as A. pisi. Identity of two isolates could not be established on morphological basis. RAPD analysis of 40 isolates grouped them into six clusters vis-a-vis geographic location. Isolates from Sangla (Kinnaur) formed cluster V, two Chamba isolates made a separate cluster I and Jinjhiali (Mandi) isolates formed three clusters viz. II, III and VI. This indicated limited exchange of seed from the one region to another and hilly terrain acting as a natural barrier for pathogen spread and maintaining region specific reproductive isolation. Nucleotide sequence analysis of ITS region helped in the confirmation of isolates as Ascochyta spp., overcoming ambiguities classical identification methods. Identity of As2 was finally settled as A. pinodes instead of A. pisi. Similarly, As3 which could not be identified as either A. pisi or A. pinodes was finally designated as A. pinodes. The phylogenetic analysis of 33 isolates grouped them into five different clades. Nucleotide sequence analysis could not differentiate A. pinodes and A. pinodella as there was considerable homogeneity. Net genetic distance between A. pinodella and A. pinodes group was zero forming clade I. A. pisi formed a separate clade II and showed lower mean/net genetic distance with A. rabiei group than A. pinodes/A. pinodella group indicating its kinship to A. rabiei. Similarly isolate As44 infecting chickpea was clustered in clade III making it distinct species infecting pea. As43 isolated from Vigna mungo formed clade IV. The genetic distance within individuals of a species was 0.007, 0.005, and 0.001 for A. pisi, A. pinodella and A. pinodella, respectively. The lowest genetic distance (0.001) within individuals of A. pinodes indicate capability of A. pinodes to undergo sexual reproduction. This means A. 32 pinodes has a better capability to evolve and thus adapt in changed environmental conditions and better survival in adverse conditions. This could explain A. pinodes to be predominant Ascochyta spp. infecting pea as compared to the dominance of A. pisi in 1980's in Himachal Pradesh. The evaluation for resistance of three hundred and sixty seven pea genotypes collected from various sources by detached leaf method revealed all the genotypes to be susceptible to Ascochyta pinodes indicating lack of diversity resistance in pea. Different mutants generated in the Department of Vegetable Science and Floriculture did not show any effective resistance. Pea plants treated with 3mM SA exhibited highest PAL and PO activity and delayed the symptom expression indicating it's effectiveness in induction of SAR. These preliminary efforts to induce resistance in pea indicate the possibility of exploitation of systemic acquired resistance for ecofriendly management of Ascochyta blight of pea.
 
Date 2009
 
Type Thesis
NonPeerReviewed
 
Format text
 
Language en
 
Identifier http://hillagricrepository.co.in/830/1/Vikas%20Kapoor.pdf
Kapoor, Vikash (2009) Molecular Characterization of Ascochyta Spp. Causing Pea Blight and Evaluation of Resistance. PhD thesis thesis, CSKHPKV Palampur.