Stem, leaf and cotyledon resistance responses to a prevalent Sclerotinia sclerotiorum pathotype in Australia highlight new opportunities to improve white mould resistance in common bean

Context White mould (Sclerotinia sclerotiorum) inflicts major yield losses on common bean (Phaseolus vulgaris); yet, commercial cultivars known for their high yields and market-adapted grains lack physiological resistance to this disease.Aims This study aimed to test diverse common bean genotypes for resistance in stem, leaf and cotyledon tissues.Methods Thirty-four common bean genotypes with a wide range of agronomic traits and grain types, including genotypes noted previously for susceptible and resistant responses to white mould, were inoculated with the prevalent S. sclerotiorum isolate MBRS-1. Then they were assessed for resistance in stem, leaf and cotyledon tissues under controlled environment conditions, by inoculating plants with a 105mL−1 hyphal fragment concentration.Key results There was significant (P<0.001) variation in resistance responses in stem, leaf and cotyledon tissues across the genotypes. Contender, ICA Bunsi, XAN 280 and Taisho-Kintoki showed the highest resistance in stems, whereas Norvell 2558, Pico de Oro, Sanilac, Othelo and Negro Argel exhibited notable resistance in leaves. Metis, Canario 107, Pico de Oro, Pogonion and Jubilejnaja 287 displayed the most resistance in cotyledons.Conclusions This is the first reported attempt to determine the response of common bean germplasm to a prevalent pathotype of S. sclerotiorum in Australia. Bean genotypes exhibiting high-level resistance to white mould identified in this study can be used as parental lines for crosses in common bean breeding programs and/or directly as improved cultivars.Implications The study highlighted both the value of screening under controlled environmental conditions to reliably locate new stem, leaf and/or cotyledon resistances and the possibility of using rapid cotyledon screening to indicate stem resistances because the expression of resistances in cotyledons generally correlated strongly with those in stems.