LAUSR

We determined the species composition of 219 isolates of potato blackleg or soft rot pathogens in Japan collected after 2000 from potato plants by species-specific PCR. Of the total, Pectobacterium wasabiae (Pw) and P. carotovorum subsp. brasiliense (Pcb) comprised 88% (Pw: 94 isolates, Pcb: 98 isolates) of the isolates and Dickeya dianthicola (Ddi) 12% (27 isolates). P. atrosepticum (Pa) was not detected. Genetic diversity of Pw, Pcb and Ddi was investigated using repetitive sequence-based PCR (rep-PCR) fingerprinting with three primer pairs complementary to repetitive sequences in the bacterial genome (BOX, ERIC and REP). One hundred and twenty-one Pw isolates, one hundred Pcb isolates and thirty-three Ddi isolates were assigned to twenty-nine, twenty-one and eleven fingerprint genotypes (FGs) based on the combination of fingerprint patterns for each rep-PCR experiment (BOX-, ERIC- and REP-PCR). The genetic diversity of Pw and Ddi isolates in Japan was considered high, with Simpson’s diversity index and Shannon’s index of 0.87 and 2.44 for Pw, and 0.84 and 2.05 for Ddi, respectively. Pcb isolates were less diversified genetically (diversity index: 0.57 and 1.58). The FGs of the isolates obtained from blackleg-affected potato plants in the seed tuber field agreed with those of the isolates in the field where the seeds produced were grown. These results support the occurrence of seed-borne transmission of the blackleg pathogen between the fields.