Ashy stem blight and white mold caused by Macrophomina phaseolina (Tassi) Goidanich and Sclerotinia sclerotiorum L. de Bary, respectively are important fungi pathogens affecting common bean (Phaseolus vulgaris L.) worldwide. Genetic resistance is the most environmental friendly approach to control both diseases. Our objective was to evaluate the response of Phaseolus spp. germplasm to three fungal isolates. Two runner bean accessions (P. coccineus L.), and 23 common bean genotypes including 10 UPR-Mp breeding lines derived from multiple-parent crosses were inoculated with the NY133 S. sclerotiorum isolate and PRI21 and PRI24M M. phaseolina isolates by the cut-stem method in the greenhouse. The disease severity was evaluated at 35 days post-inoculation. Middle American common beans ‘Othello’, TARS-MST1, and ‘Verano’ were susceptible (mean scores > 6.5) to all fungal isolates whereas the runner beans PI 183412 (Sel-1 and Sel-2) and breeding line UPR-Mp-57 were susceptible to NY133. Andean common beans A 195, ‘PC 50’, PRA154, PRA155, and VA 19 were intermediate (scores 4-6) to NY133, PRI21, and PRI24M. In contrast, Middle American beans 92BG-7 and BAT 477 were intermediate to NY133 and PRI21, and susceptible to PRI24M. The runner beans PI 183412-Sel-1 and PI 183412-Sel-2, and common bean breeding lines UPR-Mp-22, UPR-Mp-48, UPR-Mp-54, and UPR-Mp-57 were resistant (scores < 3.5) to PRI21 and intermediate to PRI24M. Conversely, UPR-Mp-34 and UPR-Mp-54 were resistant to NY133. This information should help to select parents with higher levels of resistance that may be used in breeding programs for both diseases.
