Genetic diversity of Erwinia chrysanthemi pv. zeae causing bacterial stalk rot of maize and its management

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Date
2015
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Punjab Agricultural University, Ludhiana
Abstract
Disease surveys conducted during Kharif 2012 and 2013 in different maize growing areas of Punjab revealed that the incidence of bacterial stalk rot was high in the district of Hoshiarpur and SBS Nagar. Maximum disease incidence (70%) and severity (20%) was recorded on Dekalb Double hybrid during Kharif 2012, while, in 2013 maximum disease incidence (25%) and severity (5%) was recorded on DKC 9106 hybrid of maize. It was also observed that disease incidence and severity was comparatively higher in flat sown crop than ridge sown. A total of 62 isolates of Erwinia chrysanthemi pv. zeae were recovered from diseased stalks from different districts of Punjab. The isolates were grouped as less, moderately or highly virulent and their virulence was positively correlated with the amount of pectate lyase enzyme produced by the respective isolates. The banding pattern of the Pel gene and rDNA primers further confirmed this pathogen to be Dickeya zeae. Phenotypic characterization of this pathogen revealed multiple antibiotic resistance in the population of E. chrysanthemi pv. zeae in Punjab. The pathogen was found to be highly variable when tested on a set of inbred lines/hybrids with five isolates viz. M-7, M-9, M-13, M-14 and M-29 being highly virulent on almost all the lines tested. The isolates were further assessed by using RAPD and CRISPR based markers, which revealed high level of genetic diversity. Both the marker systems were found to be highly polymorphic. Unique alleles from CRISPR analysis were further sequenced for sequence analysis. It was found that direct repeats in the sequenced alleles matched with Dickeya spp. and other Enterobacteriales, while spacer DNA regions were highly variable and unique. For the management of bacterial stalk rot advanced germplasm lines were screened against most virulent isolate of Erwinia chrysanthemi pv. zeae. Twenty lines found to be moderately resistant. The level of resistance was further correlated with production of antioxidative enzymes. Field trials on chemical control of this disease revealed that drenching or dusting with bleaching powder was effective for the management this disease.
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