IMPROVED SEED TREATMENTS FOR CONTROL OF BACTERIAL CANKER OF TOMATO

Tomato seeds systemically infected with Clavibacter michiganensis subsp. michiganensis were variously treated for disinfection and transplants raised from these seeds in the greenhouse were planted in field plots. Seed infection was determined by plating seeds on CNS agar. Seeds soaked in 0.1 M hydrochloric acid (HCl) or 0.05% (w/v) o-hydroxydiphenyl for 1 h germinated equally well whether or not they were rinsed with water afterwards. In 1989, soaking infected (83%) seeds in 0.1 M HCl or 0.05% o-hydroxydiphenyl for 1 h reduced seed infection to less than 1% and field incidence of primary canker to less than 2% compared with 24% in infected check plots; seed treatment with hot (50-degrees-C) 0.6% sodium hypochlorite (NaOCl) solution for 15 min reduced seed infection to zero but primary canker incidence was 4.5% in the field plots. Again in 1990, soaking infected (93%) seeds in 0.96% NaOCl solution, applied at the rate of 0.1 g NaOCl per g seed, for 1 h at 25-degrees-C reduced seed infection to 0.5% but field incidence of primary canker was 10% compared with 55% in the infected check plots. These rates of primary canker incidence in NaOCl treatment plots led to a relatively high proportion of seed infection in harvested fruits, 45% in 1989 and 73% in 1990. There was no seed infection in harvested fruits of HCl or o-hydroxyphenyl treatment plots in 1989 compared with 97% in the infected check plots.