Pathogenicity of soft rot erwinias to potato plants in Scotland and Israel

摘要

The pathogenicity ofErwinia carotovorapv.carotovora, E. carotovorapv.atrosepticaandE. chrysanthemito potato plants was examined in experimental and commercial crops in Scotland and Israel in 1983 and 1984. Symptoms caused by the three erwinias tended to be different depending on when they were expressed during the different growing seasons. Field symptoms were grouped into four types based on the origin and extent of stem rot and of leaf desiccation. Most were reproduced on inoculated potted plants held under different combinations of relative humidities (ca70 andca100) and temperatures (17° and 30°C). In plots planted with seed inoculated withE. c. atrosepticaalone or together withE. c. carotovoraorE. chrysanthemi(in Israel only), stem rot symptoms developed throughout the growing season in Scotland (Invergowrie) but only before May in February‐sown crops and after November in September‐sown crops in Israel (Negev). In contrast,E. chrysanthemialone or together with one or the other erwinias in Israel caused extensive leaf desiccation with no stem rot only in May and before December in the spring‐and autumn‐sown growing seasons, respectively. None of 13E. c. carotovorastrains inoculated into erwinia‐free tubers was pathogenic in the spring growing season in Israel. More than one erwinia type was frequently present in both healthy and diseased stems, usually the same bacteria which were inoculated in ihe seed tubers. Isolations made from diseased stems showed that the temporal patterns of detection frequency ofE. c. atrosepticaandE. chrysanthemiin stem rots and in plants with leaf desiccation symptoms were similar to those for expression of the two symptom types.Erwinia carotovorapv.carotovoraalone was never found in diseased stems although it could be isolated together with the other erwinias in both Scotland and Israel. Similar results were obtained when diseased stems from commercial potato fields were examined, except thatE. c. carotovorawas the sole erwinia present in aerial stem rots. The patterns observed in the pathogenicity of three erwinias were tentatively explained in terms of temperature changes during the growing season, the transition points being in the region of 20°C for maximum soil temperature at tuber depth or 25°C for maximum air temperature above whichE. c. atrosepticaand below whichE. chrysanthemiwere not apparent