SURVIVAL OF XANTHOMONAS-CAMPESTRIS PV TRANSLUCENS BETWEEN SUCCESSIVE WHEAT CROPS IN ARKANSAS

Reducing the level of initial inoculum may be a feasible means of cont rolling bacterial streak and black chaff of wheat caused by Xanthomona s campestris pv. translucens. The objective of this research was to de termine the principal source of inoculum under Arkansas conditions. Us ing artificially infested seeds, a rifampicin-resistant mutant of the pathogen (strain 88-14(Rif)) was established in field plots of wheat c ultivars Florida 302 (susceptible) and Terral 101 (moderately resistan t) at two locations and in a plot of Florida 302 at a third location. Bacterial streak caused by strain 88-14(Rif) developed in all plots. S train 88-14(Rif) was not detected in crop debris, soil, or possible al ternative host plants in the field 3 mo after harvest at any location. No bacterial streak symptoms were observed at any location on Florida 302 planted with disinfested seed 4 mo after harvest. However, strain 88-14(Rif) was isolated from one of 480 Florida 302 leaves assayed fr om one location at one sampling time. The percentage of harvested seed infested with strain 88-14(Rif) 2 mo after harvest ranged from 9.8 to 37.7% for Florida 302 and from 0.3 to 5.3% for Terral 101. Under grow th chamber conditions, transmission of seedborne strain 88-14(Rif) to seedlings ranged from 4.0 to 24.5% for Florida 302 and from 0.0 to 0.2 % for Terral 101. Under field conditions, however, strain 88-14(Rif) w as isolated only from one seedling of one Florida 302 seed lot. Based on the poor survival of the pathogen in the field and the relatively h igh percentage of infested seed and transmission to seedlings under gr owth chamber conditions for the susceptible cultivar, infested seed is suspected to be the principal source of inoculum.