INTERACTIONS BETWEEN Colletotrichum coccodes AND Ralstonia solanacearum ON THREE POTATO CULTIVARS

The two most important diseases of potato in Hamedan province are black-dot disease caused by Colletotrichum coccodes and bacterial wilt disease caused by Ralstonia solanacearum. In this study interactions between the two pathogens were surveyed on the three potato cultivars, Agria, Boren and Diamant using two inoculation methods. Data analysis revealed that co-inoculation of potato by both pathogens showed pathogenicity synergistic effect, and potato length and stems and roots weight were decreased. In Agria, R. solanacearum increased C. coccodes effectiveness on potato plants. Agria cultivar root colonization by C. coccodes sclerotia was more than other cultivars and was scored as 50 – 70%. In fact, this cultivar was more susceptible to C. coccodes than others. Pathogenicity of C. coccodes and R. solanacearum on Boren potato cultivar were almost equal and potato length and stems and roots weight were decreased in compare to control plants. At the presence of two pathogens plant parameters were more decreased. In this cultivar root colonization by C. coccodes sclerotia was scored as 50%. In most cases, Rs treatment on Diamant has no significant differences with control plants and there was relative resistance to the bacterial wilt in this cultivar. In compar to other cultivars, root colonization in Diamant was low and scored 30 %. Diamant potato cultivar was more resistant than others to C. coccodes.