Evaluation of common bean accessions for resistance to Pythium ultimum

Abstract

Common bean accessions were evaluated to identify white- or light-seeded beans with resistance to Pythium ultimum Trow. In total, 568 common bean (Phaseolus vulgaris L.) accessions were inoculated with a hyphal suspension of P. ultimum under greenhouse conditions. The bean accessions included represented the Andean-Middle American core collections (406 accessions) and 162 additional white- or cream-seeded accessions. The accessions were categorized into 12 groups according to seedcoat color. Accessions with light seedcoats exhibited higher levels of disease symptoms, with white-seeded bean accessions being the most susceptible class. No symptomless white-seeded accessions were identified. The most resistant white-seeded accessions were PI 430207, PI 527803, PI 290996, PI 299021, PI 194574, and PI 304110. Cream-seeded beans exhibited higher levels of resistance, with nine accessions rated as symptomless out of 188 cream and white accessions tested. Of 568 accessions, 48 tested were symptomless, whereas disease ratings of the other accessions ranged from resistant to highly susceptible.