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    Efforts are currently underway in the Rowland laboratory to develop genetic linkage maps for blueberry that are saturated enough to map QTLs controlling chilling requirement and cold hardiness. Initial (relatively low density) maps have been constructed using RAPD and EST-PCR markers for diploid populations shown to be segregating for both chilling requirement and cold hardiness. The populations resulted from testcrosses between F1 interspecific hybrids, V. darrowi x diploid V. corymbosum, and another V. darrowi clone and another diploid V. corymbosum clone. The map of the V. corymbosum testcross currently comprises approximately 90 RAPD and EST-PCR markers and the map of the V. darrowi testcross comprises approximately 70 RAPD and EST-PCR markers (Figs. 1 and 2). In addition, large portions of both populations have been evaluated for chilling requirement and cold hardiness and a generation means analysis has been used to study the inheritance of cold hardiness in the cold-acclimated state. Results from the generation means analysis indicated that the cold hardiness data best fit a simple additive-dominance model of gene action (a model in which the genes controlling cold tolerance are assumed to have simple additive and dominance effects).  Furthermore, in this study, the magnitude of the additive gene effect was greater than that of the dominance gene effect. A preliminary QTL analysis using the current genetic linkage map and cold hardiness data for the V. corymbosum testcross population has identified one putative QTL associated with cold hardiness that explains ~20% of the genotypic variance. Also, three markers have been identified that show significant association with cold hardiness/cold sensitivity from an analysis of variance in each of the V. corymbosum and V. darrowi testcross populations.