Are Sclerotinia sclerotiorum populations from the tropics more variable than those from subtropical and temperate zones?

Abstract

The genetic variability of Sclerotinia sclerotiorum populations has been investigated in many countries and, consequently, under different ecological conditions. The first studies were conducted to gather information about the genetic structure of populations sampled in temperate climate areas. Based on DNA fingerprinting analysis of restriction fragment length polymorphism (RFLP) data and mycelial compatibility groups, most studies revealed a clonal population structure. Later, using DNA sequences, populations from subtropical regions of North America were reported to be more variable than those from temperate regions. In the past few years, new analyses in temperate, sub-tropical and tropical areas were conducted using microsatellite (SSR) markers. Most studies using SSR reported both high variability and evidence of outcrossing in S. sclerotiorum populations, but evidence of clonality has also been found. Some authors argue that populations from subtropical and tropical areas are more diverse. We argue that the reports of high variability of S. sclerotiorum in tropical or subtropical regions may be due to an increase in the number of studies performed with SSR markers in these regions and in some cases due to inappropriate interpretations of the results.