Unleashing the potential of multitrait onion seed endophytic bacteria in combating purple blotch incited by Alternaria porri (Ellis) Cif

Onion purple blotch incited by Alternaria porri is a serious bottleneck in sound cultivation of crop. The management of disease through the use of fungicides is matter of concern owing their indispensable impact on environment. A paradigm shift toward use of eco-friendly management tactics involving the use of seed endophytes presents new frontiers in research. The endophytic bacteria retrieved from onion seeds (Hisar Onion 2) presented diverse range of biocontrol and plant growth promoting traits. Dual culture assay revealed pre-eminence of OSEB 11 (72.35 per cent) and OSEB 3 (67.06 per cent) in supressing mycelial growth of Alternaria porri. Ten bacterial isolates exhibited ammonia excretion, seven isolates were recorded positive for siderophore production, four isolates presented cyanogenic potential while five isolates exhibited cellulase activity. OSEB 1, OSEB 12 and OSEB 14 were found positive for all the performed biocontrol and plant growth promoting traits. The MALDI TOF based characterization of promising endophytic bacteria revealed identity of OSEB 3 as Enterobacter cloacae and that of OSEB 11 as Stenotrophomonas maltophila. In planta evaluation of promising endophytes indicated that foliar spray of Stenotrophomonas maltophila was highly influential in enhancing phenolics and antioxidant enzymes (peroxidase, polyphenol oxidase and phenylalanine ammonia lyase) in onion with consequent suppression of purple blotch disease, leading to 41.80 per cent management over control. Field evaluation of promising endophytes also revealed efficacy of foliar spray of Stenotrophomonas maltophila in supressing the disease (33.85 per cent disease management over control) and enhancing seed yield.