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