Bacteria Associated with Onion Foliage in Michigan and Their Copper Sensitivity

Abstract

Bacterial stalk and leaf necrosis of onion, Allium cepa L., is a concern of Michigan producers. Plants with symptoms of bacterial stalk and leaf necrosis were collected in 2013 and 2014 from 17 fields in six Michigan counties. Bacterial isolates were identified using Biolog and confirmed by sequencing the 16s rDNA gene. From a total of 414 isolates, 10 bacterial species were identified. Pantoea agglomerans (42.5%), Pantoea ananatis (17.4%), and Enterobacter cowanii (7.5%) were most prevalent and were tested for pathogenicity on onion foliage and bulbs. More P. ananatis isolates (92%) were pathogenic on seedlings than P. agglomerans or E. cowanii isolates (approximately 50%). When 197 bacterial isolates were tested for sensitivity to copper hydroxide (200 µg/ml), 41% of P. agglomerans isolates were found to be tolerant to copper hydroxide, whereas 19 and 22% of P. ananatis and E. cowanii isolates were tolerant, respectively. Identifying the bacterial species associated with foliar disease symptoms on onions in Michigan, their pathogenicity and tolerance to copper is an important step in developing improved disease management strategies.