Black rot disease caused by bacteria Xanthomonas campestris pv. campestris is one of the destructive diseases that affect cabbage plant. However, host- pathogen interaction study is not yet documented in cabbage growing area of southwest Ethiopia. Therefore, the objectives of this study were to know host pathogen interaction of the pathogen strains collected from major cabbage growing areas of southwest Ethiopia. The study was carried out in the green house and were conducted with 4 isolates x 6 cabbage varieties factorial treatment combinations in randomized complete block design replicated three times. There were a highly significant differences (p<0.001) in incubation period (IP), date of complete death (DD) and percentage severity index (PSI). Cabbage variety Love f1 and Green halo f1 showed high resistance reaction, respectively to all isolates with low mean severity index of 3.31% and 4.05%, respectively; whereas Copenhagen, Hot f1 and kale were susceptible to all isolates showing high mean percentage severity index of 52.32%, 48.47% and 47.49% respectively. Among the isolates, BB2 isolate from Jimma area was highly pathogenic to Copenhagen, Hot f1 and Kale cabbage varieties as compared to the Mana (MGB1), Kersa (KM1) and S/Chekorsa (SCDG3) isolates which are moderate. However, more extensive studies have to be undertaken for identifying and developing management of black rot for cabbage production that may contribute to stabilizing cabbage production in Ethiopia.

Keywords: Black rot, Plant pathogen, Resistant cultivar