SURVIVAL OF THE PHYTOPATHOGEN ERWINIA-CAROTOVORA SUBSP CAROTOVORA IN STERILE AND NONSTERILE SOIL, SAND AND THEIR ADMIXTURE

Survival of phytopathogens in irrigation water and irrigated soil is o f major concern to the agricultural community. In the present study, a n Erwinia carotovora subsp. carotovora strain was tested for survival capability in three non-sterile and heat-sterilized soil matrices (soi l, sand and soil + sand) over 35 d. In all non-sterile soil matrices, Erw. carotovora subsp. carotovora numbers declined below the detection limit over 35 d, the main variance being the decline rate related to nutrients available in the different matrices (soil, soil + sand and s and respectively). In heat-sterilized soil and soil + sand matrices Er w. carotovora subsp. carotovora revealed a regrowth, while in sterile sand matrix its decline was lower over the same time period. In previo us published reports, when soil was sterilized by irradiation, such a regrowth was not observed. Application of an initial single load of so dium nitrate solution (70 mg l(-1)) was found to extend bacteria survi val rate in non-sterile and sterile soil columns. In sterile soil colu mns supplemented with sodium nitrate, Erw. carotovora subsp. carotovor a did survive well for up to 60 d, with a major regrowth over the firs t 12 d and decline up to day 60, reaching initial loading numbers. The information on the potential survival of Erw. carotovora subsp. carot ovora in soil for up to 35 d and regrowth in sterile soil should be of concern, especially when irrigation is performed with poor quality wa ter.