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

Freezing tolerance is the ability of plants to survive subfreezing tem peratures and is a major component of winter survival. In order to stu dy the genetic regulation of freezing tolerance, an F2 population of B rassica rapa and a doubled haploid population of Brassica napus were a ssayed in vitro for relative freezing tolerance of acclimated and nona cclimated plants. Linkage maps developed previously were used to ident ify putative quantitative trait loci (QTL). Genomic regions with signi ficant effects on freezing tolerance were not found for the B. napus p opulation, but for B. rapa four regions were associated with acclimate d freezing tolerance (FTA) and acclimation ability (FTB), and two unli ked 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, b ut negative dominance effects. RFLP loci detected by a cold-induced an d 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.