Biology and Management of Bacterial Spot of Peppers in Oklahoma.

Bacterial spot, an important disease of bell and chili peppers grown in Oklahoma, is caused by . We evaluated isolates from 1995 to 2015 ( = 72) for avirulence alleles and race by assessing hypersensitive responses (HRs) on differentials with resistance genes , , , or . Most isolates (96%) expressed (races 1, 3, 7, 8), and only three were virulent on (race 6). Chili cultivars, grown locally for capsaicin production, were susceptible to all races. Copper-based spray programs were evaluated on bell pepper hybrids with and without resistance from 2008 to 2010 and on bell and jalapeño hybrids with or from 2017 to 2018. and hybrids generally had lower disease and higher yields (≤21 t/ha) than susceptible entries. Copper reduced disease by 20 to 40% and increased yield by an average of 4 t/ha, but yield responses were not always significant ( = 0.05). In August 2018, disease increased to >50% on hybrids but remained low on the hybrid. Despite the breakdown of resistance, yields of the hybrids were not reduced. Avirulence alleles and race of isolates from susceptible, , and hybrids at the end of the 2018 trial depended on source plant genetics. was expressed in 86% of isolates from a susceptible hybrid but not in any isolates from the and hybrids. HR resistances effectively protected yield, but their deployment may not be sustainable without cultural practices such as crop rotation that limit pathogen survival and transmission to subsequent crops.