Mycelial Compatibility Groups in Texas Peanut Field Populations ofSclerotium rolfsii

Abstract

Sclerotium rolfsii isolates (366) collected from 1985 to 1994 in Texas peanut fields were placed in 25 mycelial compatibility groups (MCG) based on the formation of an antagonism zone between incompatible mycelia of paired isolates. The same MCG were often detected in several geographically distant counties in Texas. Individual peanut fields contained one to five MCG, whereas individual plants were infected with isolates from one MCG. Two fields sampled extensively in 1992 maintained the same MCG in 1993 : MCG 6 and 7 in Galen and MCG 1, 2, 3, 4, and 12 in Grissom. However, MCG 11, which consisted of a single fungicide-tolerant 1985 isolate of S. rolfsii from Galen, was not found among the 366 isolates collected nor was the trait of fungicide tolerance. DNA amplification patterns resulting from the use of the 18-base oligonucleotide primer NK2 and from restriction digests of the internal transcribed spacer (ITS) region of the rDNA were examined in a subset of 80 isolates from four fields to determine the genetic similarity of isolates within and between 12 MCG. Three NK2-amplified DNA patterns in genomic DNA and four MboI restriction digest patterns of the ITS region were found. All isolates within a MCG gave identical patterns for each marker, and some MCG shared the same ITS and NK2 patterns. MCG sharing the same DNA patterns were often from the same field.