<Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">alliifistulosi</Emphasis> pv. nov., the causal agent of bacterial leaf spot of onions

In 1972, bacterial leaf spot of onion (BLSO) was first recorded in Japan by Goto. The pathogen was considered as a pathovar of Pseudomonas syringae specifically causing disease on onion and Welsh onion, but it has not been taxonomically investigated in detail. In 2012 and 2014, a disease suspected as BLSO re-emerged on onion in Shizuoka and Hyogo Prefectures, Japan, respectively. A pathogenic bacterium isolated from the infected onions was thought to be the BLSO agent after preliminary examinations. Strains isolated from BLSO in 1969, 1986, 1987, 2012 and 2014 were characterized and compared with the causal agent of bacterial blight of leek (P. syringae pv. porri), which causes similar symptoms on Allium plants. The result of rep-PCR distinguished the BLSO agent from P. syringae pv. porri. Multilocus sequence analysis on housekeeping genes and hrp genes encoding the type-III secretion system revealed that the strains of the BLSO agent clustered independently of P. syringae pv. porri. The BLSO agent and P. syringae pv. porri also differed in utilization of erythritol, dl-homoserine, glutaric acid and other bacteriological characteristics and caused different reactions on onion, Welsh onions, chives, shallot, rakkyo, leek, garlic and Chinese chive. Thus, the BLSO agent clearly differs from P. syringae pv. porri and is considered to be a new pathovar of P. syringae. The name P. syringae pv. alliifistulosi is proposed with pathotype strain ICMP3414.