Testing inoculation methods and sources of resistance to the halo blight bacterium (Pseudomonas syringae pv. phaseolicola) in Phaseolus vulgaris

Summary

A comparative test of six inoculation methods was conducted using 2 halo blight race 2 virulent strains, Nebr. HB 16 and HB 21 (Pseudomonas syringae pv. phaseolicola), on five dry bean cultivars/lines (Phaseolus vulgaris L.) of known resistance and susceptibility. The water-soaking of leaves method caused the most severe reaction among the leaf inoculation methods, followed by the carborundum, spraying and multiple needle methods, respectively. The seed soaking method was considered too severe to be useful, since entries identified as resistant by the other methods, were susceptible with the former method. Great Northern Nebraska # 1 sel. 27 and PI 150414 had the highest level of leaf resistance, but the former developed systemic chlorosis with the stem stabbing method, but not the latter line. No systemic chlorosis was seen in either line with the other methods of inoculation. This suggests that there may be a different genetic mechanism conferring resistance/susceptibility to the toxin in these two lines when the stabbing method is used. No interaction occurred between method by genotype and isolate by method but significant interactions occurred between genotype by isolate and method by isolate by genotype. The leaf and pod reaction of forty cultivars/lines to the new halo blight Nebr. Charlevoix strain was also determined. Different combinations of degrees of resistance and susceptibility of leaves and pods were observed. GN Tara, GN Harris, and PI 150414 had the highest combination of leaf and pod resistance.