Selection of pea genotypes with partial resistance to Sclerotinia sclerotiorum across a wide range of temperatures and periods of high relative humidity

Abstract

Partial resistance to Sclerotinia sclerotiorum based on stem lesion advancement was assessed for nine wild pea genotypes from five geographic origins and two cultivated genotypes, when peas were inoculated and incubated at all combinations of five temperatures (15.6, 18.3, 21.1, 23.9, 29.4°C) and four period(s) of high relative humidity (PHRH; 12, 24, 48, 72 h). PHRH of 12 and 24 h should not be used when screening plants for resistance to S. sclerotiorum regardless of the incubation temperature, since stem lesions are rarely (2.7%) visible at 12 h and there were no significant differences (P ≤ 0.05) in lesion lengths among and within genotypes at all temperatures assessed after 24 h. However, PHRH of 48 and 72 h are recommended for use to assess partial resistance since significant differences in stem lesion length among the genotypes were observed and characterized for these periods. Genotypes with cool (15.6 and 18.3°C) versus warm (23.9 and 29.4°C) temperature partial resistance to S. sclerotiorum were identified, and genotypes PI 240515 and PI 169603 appear to have the best cool and warm temperature partial resistance, respectively, among the genotypes assessed. A temperature of 21.1°C was the optimal temperature favouring lesion advancement for the majority of the genotypes evaluated. PI 169603 demonstrated the best partial resistance to S. sclerotiorum across the widest temperature and PHRH ranges and is recommended to plant breeders as the best single genotype to develop future cultivars with improved partial resistance to S. sclerotiorum based on stem lesion advancement.