Mycelial compatibility groups in Buenos Aires field populations of Sclerotinia sclerotiorum (Sclerotiniaceae)

Abstract

One-hundred and forty isolates of Sclerotinia sclerotiorum (Lib.) DeBary were obtained in a 6500-km² area of the Buenos Aires Province. These isolates were collected from soybean (60 isolates), lettuce (59 isolates) and sunflower (21 isolates) fields. Fifty different mycelial compatibility groups (MCGs) were distinguished overall, 27 of which consisted of two or more isolates. Populations of S. sclerotiorum were made up by numerous MCGs and shared a similar frequency profile regardless the locality or the date of sampling. MCG occurrences differed among the crops, only two MCGs were shared by the three crops and approximately 60% of the MCGs were unique for each crop. The Shannon diversity index (H_o) of MCG for the whole region was 0.314 (H_tot). Partition of total diversity (H_tot) showed that 98.4% corresponded to variations of diversity within populations. Morphological characteristics were not significantly different among MCGs, except for the dry weight per sclerotium. On the basis of the detached celery petiole assay, there were no differences in aggressiveness between MCGs either. However, isolates collected from sunflower plants were more aggressive than those collected from soybean, regardless the MCG they belonged. Aggressiveness was positively correlated to colony radial growth. After principal component analyses (PCA) were performed, it could be identified a main central group of isolates and two other smaller groups. Main contributors to the total variance were the percentages of large sclerotia, the dry weight per sclerotium and the percentages of medium and small sclerotia.