Multi-year evaluation of Clavibacter michiganensis subsp. sepedonicus disease symptoms in cultivated potato genotypes

The expression of foliar and tuber bacterial ring rot (BRR) symptoms in 108 cultivated potato genotypes inoculated with Clavibacter michiganensis subs p. sepedonicum was examined in field experiments during 1986 to 1996. Consi derable variation in the incidence of foliar ERR symptoms was observed in a ll plant cultivars, ranging from no detectable symptoms to complete necrosi s of the leaves. Similar variability was observed in the incidence of tuber ERR symptoms, and severity of tuber symptoms ranged from no detected sympt oms to complete breakdown of the vascular ring that extended throughout the tuber. A decline in the incidence and severity of tuber, but not foliar sy mptoms, was observed in the later years of the study (P<0.05). Foliar and t uber ERR symptoms generally were positively correlated (P<0.01) prior to 19 93 but not in subsequent years (P>0.05) when tuber symptoms declined. Stron g correlations mere observed between the incidence and severity of foliar E RR symptoms (r=0.41, P<0.01) and between the incidence and severity of tube r ERR symptoms (r=0.96, P<0.001). During the 11 year period, no ERR symptom s mere observed in 2,620 uninoculated control plants.