Impact of flower age and colour on infection of bean and alfalfa by Sclerotinia sclerotiorum

Abstract

Sclerotinia sclerotiorum is the causal agent of white mold of common bean (Phaseolus vulgaris) and blossom blight of alfalfa (Medicago sativa). No resistant cultivars of bean and alfalfa are currently available to growers in Canada. Studying physiological resistance is an important first step toward assessing and developing resistance in commercial cultivars. Flowers are generally the first tissue to be colonized by S. sclerotiorum in bean and alfalfa, and petal age has recently been shown to affect infection by S. sclerotiorum in canola (Brassica napus). Therefore, the development of the pathogen on detached flowers of bean and alfalfa was examined, focusing on the impact of flower colour and age on ascospore germination and mycelial growth. The colour and age of bean flowers did not affect ascospore germination or mycelial growth. Germtube growth was faster in extracts of 1-day-old petals than in extracts of 7-day-old petals for some cultivars. Petal extracts of bean had no inhibitory effect on ascospore germination and fungal growth, regardless of petal age and colour. Coloured flowers (purple or yellow) of alfalfa were colonized more slowly than white flowers. There was no difference in ascospore germination or mycelial growth in aqueous extracts from alfalfa petals of different colour, age or number. Petal age and colour did not have a substantial effect on the germination and development of S. sclerotiorum in alfalfa and bean.