A Radiation-induced Mutant with Resistance to Common Bacterial Blight Disease in Common Beans

The leaf reaction of the Phaseolus vulgaris L. germplasm—UNECA (M6 mutant derived from the cultivar Chimbolito, Costa Rica), ‘Chimbolito’, BAC-6 (Brazil), XAN159 (Centro Internacional de Agricultura Tropical, Cali, Colombia), and ‘PC-50’ (Domican Republic)—to Xanthomonas campestris pv. phaseoli strain V4S1 (Dominican Republic) were determined in two replicated trials conducted in a greenhouse in Lincoln, Neb. (Feb.– Mar. and July–Aug. 1993). ‘PC-50’ and ‘Chimbolito’ were susceptible to Xcp strain V4S1 in both tests. UNECA, BAC-6, and XAN-159 had similar levels of resistance to Xcp in the July to August trial. However, in the February to March trial, the resistance of UNECA was greater than that of BAC-6 but less than that of XAN-159. tration was 1.5 × 10 colony-forming units/ml in a 12.5 mM standard potassium buffer with 10 mM magnesium sulphate. We used the multiple-needle method of inoculation (Andrus, 1948). Two leaflets of each trifoliolate leaf were inoculated with Xcp; the third leaflet was inoculated with only potassium buffer (control). The disease reaction was recorded 15 days after inoculation by visual inspection as the percentage of the inoculated leaf area developing common bacterial blight symptoms, such as necrosis, water soaking, or chlorosis. The mean percentage of the inoculated leaf area with common blight symptoms was recorded for eight plants per replication. A combined analysis of variance over planting dates was performed using arcsin-transformed values, and treatment means were separated using Duncan’s multiple range test at P ≤ 0.05.