Variation in oxalic acid production, mycelial compatibility and pathogenicity amongst isolates of Sclerotinia sclerotiorum causing white mold disease

Sclerotinia sclerotiorum is an important devastating necrotrophic plant pathogen infecting various horticulture crops in India. The present study aimed to examine the variability among S. sclerotiorum isolates from different hosts by means of mycelial compatibility grouping (MCGs), production of oxalic acid and pathogenicity. The isolates were grouped into eight MCGs (MCG A to MCG H) and the MCG data was used to calculate Shannon’s diversity index ( H ) and Simpson index ( S ). High diversity was detected for the S. sclerotiorum isolates ( H = 1.968, S = 0.845). Most of the isolates produced oxalic acid in potato dextrose agar and potato dextrose broth embedded with bromophenol blue, which was confirmed by changing the media colour from blue to yellow. A deep bright yellow colour with higher luminosity values (37.48, 36.64 and 36.84) was observed in SS1, SS3 (mustard) and SS6 (potato) isolates. The highest oxalic acid production was recorded in potato SS14 (43.25 mM) and mustard SS1 (41.11 mM) isolates, while potato isolate SS10 (10.88 mM) produced lowest oxalic acid. All isolates infect the tested plant leaves; however, lesion size and time required for infection were varied. Positive correlations were observed in S. sclerotiorum mycelial growth vs. luminosity values, mycelial dry weight vs. medium pH and mycelial dry weight vs. oxalic acid accumulation. This study indicates a high level of diversity among the S. sclerotiorum isolates from the different crops with respect to MCG, oxalic acid production and pathogenicity. Further, these results would be helpful in developing management strategies against white mold disease.