Unravelling the aetiology of Dickeya zeae using polyphasic approaches for bacterial stalk rot in maize

Abstract

Bacterial stalk rot (BSR), caused by Dickeya zeae (syn. Erwinia chrysanthemi pv. zeae), has emerged as a significant disease affecting maize crops worldwide. In this study, symptomatic maize plants were collected from diverse agroclimatic zones in India over the period of kharif 2019–2021. Various approaches, including pathogenicity tests, cultural characteristics, biochemical profiling and molecular analysis, were employed to accurately identify the collected bacterial isolates as Dickeya. Pathogenicity assessments were conducted on 40‐day‐old maize plants, following Koch's postulates, as well as through potato maceration assays. Furthermore, cross‐infectivity studies were conducted on rice, potato, tomato and banana plants. Phenotypic and biochemical characterization confirmed that all the isolates belonged to the Dickeya genus. Additionally, PCR amplification of a pel gene fragment, specific to the genus Dickeya, further verified the pathogenic isolates as Dickeya. Molecular characterization studies were performed on four isolates (UKMDZ‐3, PBMDZ‐7, TSMDZ‐11 and HPMDZ‐16), selected to represent distinct maize agroclimatic zones and four states of India, and which caused severe infections on susceptible maize cv. Early Composite. Amplification of six characteristic genome regions (16S rRNA, recN, gyrB, dnaX, recA and dnaJ) from these isolates facilitated individual and concatenated gene phylogenetic analyses, confirming their resemblance to Dickeya zeae. This study represents the first comprehensive molecular analysis of D. zeae isolates from India, providing valuable insights for future crop improvement strategies. The findings contribute to our understanding of the genetic basis of BSR in maize and offer potential avenues for genetic enhancement to mitigate the disease's impact on maize cultivation.