SCREENING TOMATO SEEDLINGS FOR RESISTANCE TO BACTERIAL SPOT

A spray-inoculation seedling screening procedure was developed for det ecting resistance to Xanthomonas campestris pv. vesicatoria (Doidge) D ye, causal agent of bacterial spot of tomato (Lycopersicon esculentum Mill.). Two-week-old transplants were preconditioned under 95 % humidi ty for 16 hours before spray inoculation and then rated for bacterial spot 2 weeks later. Resistant plants could also be distinguished from susceptible genotypes using a modified bacterial speck [Pseudomonas sy ringae pv. tomato (Okabe) Young, Dye, and Wilkiel screening procedure (cotyledon-dip technique). When results of both screening methods were compared to field ratings from three previous seasons, significant co rrelations were more frequently observed for the spray-inoculation met hod. In Summer 1991, individual plants were evaluated by the spray-ino culation technique and then were placed in the field to determine susc eptibility under field conditions. Correlations (r = 0.28 to 0.34) bet ween spray-inoculation seedling screening ratings and field ratings, a lthough low, were significant (P less-than-or-equal-to 0.0001). More t han 90% of susceptible plants could be eliminated, saving labor, space , and time.