GENETIC-ANALYSIS OF THE COMPONENTS OF WINTERHARDINESS IN BARLEY (HORDEUM-VULGARE L)

Winterhardiness in cereals is the consequence of a number of complex a nd interacting component characters: cold tolerance, vernalization req uirement, and photoperiod sensitivity. An understanding of the genetic basis of these component traits should allow for more-effective selec tion. Genome map-based analyses hold considerable promise for dissecti ng complex phenotypes. A 74-point linkage map was developed from 100 d oubled haploid lines derived from a winter x spring barley cross and u sed as the basis for quantitative trait locus (QTL) analyses to determ ine the chromosome location of genes controlling components of winterh ardiness. Despite the greater genome coverage provided by the current map, a previously-reported interval on chromosome 7 remains the only r egion where significant QTL effects for winter survival were detected in this population. QTLs for growth habit and heading date, under 16 h and 24 h light, map to the same region. A QTL for heading date under these photoperiod regimes also maps to chromosome 2. Contrasting allel es at these loci interact in an epistatic fashion. A distinct set of Q TLs mapping to chromosomes 1, 2, 3, and 5 determined heading date unde r 8 h of light. Under field conditions, all QTLs identified under cont rolled environment conditions were determinants of heading date. Patte rns of differential QTL expression, coupled with additive and additive xadditive QTL effects, underscore the complexity of winterhardiness. T he presence of unique phenotype combinations in the mapping population suggests that coincident QTLs for heading date and winter survival re present the effects of linkage rather than pleiotropy.