Identification and Characterization of a QTL for Growth of on Pine-Based Medium.

is an economically important pathogen of pine and resides in the species complex. Here we investigated the molecular processes underlying growth in by exploring the association between growth and the nutritional environment provided by the pine host. For this purpose, we subjected a mapping population consisting of X hybrid progeny to an analysis of growth rate on a pine-tissue derived medium. These data, together with the available genetic linkage map for , were then used to identify Quantitative Trait Loci (QTLs) associated with growth. The single significant QTL identified was then characterized using the available genome sequences for the hybrid progeny's parental isolates. This revealed that the QTL localized to two non-homologous regions in the and genomes. For one of these, the parent contained a two-gene deletion relative to the parent. For the other region, the two parental isolates encoded different protein products. Analysis of repeats, G+C content, and repeat-induced point (RIP) mutations further suggested a retrotransposon origin for the two-gene deletion in . Nevertheless, subsequent genome and PCR-based analyses showed that both regions were similarly polymorphic within a collection of diverse . However, we observed no clear correlation between the respective polymorphism patterns and growth rate in culture. These findings support the notion that growth is a complex multilocus trait and raise the possibility that the identified QTL contains multiple small-effect QTLs, of which some might be dependent on the genetic backgrounds. This study improved our current knowledge of the genetic determinants of vegetative growth in and provided an important foundation for determining the genes and processes underpinning its ability to colonize its host environment.