GENETIC-ANALYSIS AND MAPPING OF GENES-CONTROLLING FREEZING TOLERANCE IN OILSEED BRASSICA

Freezing tolerance is the ability of plants to survive subfreezing temperatures and is a major component of winter survival. In order to study the genetic regulation of freezing tolerance, an F2 population of Brassica rapa and a doubled haploid population of Brassica napus were assayed in vitro for relative freezing tolerance of acclimated and nonacclimated plants. Linkage maps developed previously were used to identify putative quantitative trait loci (QTL). Genomic regions with significant effects on freezing tolerance were not found for the B. napus population, but for B. rapa four regions were associated with acclimated freezing tolerance (FTA) and acclimation ability (FTB), and two unliked regions were associated with nonacclimated freezing tolerance (FTN). Acclimation ability was regulated by genes with very small additive effects and both positive and negative dominance effects. The allele from the winter parent at the FTN QTL had positive additive effects, but negative dominance effects. RFLP loci detected by a cold-induced and a stress-related cDNA from Arabidopsis thaliana mapped near two QTL for FTA/FTB. Further tests are needed to determine if alleles at these loci are responsible for the QTL effects we detected.