Molecular and biochemical bases for resistance to Alternaria blight in Indian mustard
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Date
2022
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Punjab Agricultural University, Ludhiana
Abstract
Alternaria blight of oilseed brassicas caused by Alternaria brassicae is of great economic
significance and considered the most destructive and widespread disease of all continents. The survey
was conducted for Alternaria blight in Indian mustard during the 2019-20 and 2020-21 crop seasons to
study its prevalence and to collect isolates from different geographical regions of Punjab and other
mustard growing areas of India. The disease was found to be prevalent in low to moderate form with
average disease severity of 26.97 and 22.16% in Punjab and 27.96 and 26.00% in other regions of India
during both years. The 49 isolates collected from the survey were observed to be significantly variable
in terms of cultural, morphological, and pathological characteristics. On the basis of these
characteristics, Ab31- PAU, Ludhiana isolate was found the most virulent pathotype, and Ab04-Daun
Kalan, Patiala was the least virulent isolate. The effective inoculation method against Alternaria blight
under laboratory experiment (both in detached true and cotyledonary leaf assay) was spore suspension
drop + agarose gel however, in pot experiment under polyhouse condition, the foliar spray was found
the most efficient method for the screening of germplasm. Further, 261 germplasm lines of Indian
mustard were screened against the local isolate Ab31-PAU, Ludhiana of Alternaria brassicae by foliar
spray inoculation method. The average disease severity was 47.31% (24.85-72.13%), 44.70% (21.8967.42%),
and 46.06% (23.37-69.77%) for 2019-20, 2020-21, and pooled years, respectively. Four
genotypes viz., IM-152, ZEM-3356, IM-87, and J-8 outperformed among the germplasm lines against
the pathogen. Associative transcriptomics study was done for Alternaria blight resistance, three genes
related to Alternaria blight infection (TSD2, FAD3, and AT1G45231), six genes for plant innate
immunity having NLR domain (F24L7_13, NPH4, ILL2, TIR1, FUS6, and CDC48), and two genes
related to the phenylpropanoid pathway (ABCB2 and F7A10.28) were identified. Accordingly, these
putative genes showed the importance in defense pathway mechanisms. Eighteen genotypes that
showed moderate resistant response were found to be promising w.r.t. different biochemical parameters
studied. An overall trend of an upsurge in plant secondary metabolites (glucosinolates and total
phenols) and defensive enzymes (peroxidase, superoxide dismutase, and phenylalanine ammonia-lyase)
was detected after inoculation in diverse genotypes together with the susceptible check (Rohini). A
significant negative correlation was observed between all biochemical components and percent disease
severity. The correlation was the maximum for PAL enzyme activity with percent disease severity.
Thus, these resistant genotypes may serve as an important source of resistance in breeding for
Alternaria blight resistance in oilseed Brassica.
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Citation
Bharmera, Pooja (2022) Molecular and biochemical bases for resistance to Alternaria blight in Indian mustard (Unpublished Ph.D. Dissertation). Punjab Agricultural University, Ludhiana, Punjab, India.