Mapping of quantitative trait loci controlling timing of bud flush in Salix

Dormancy release is an important phenological stage, which determines plant growth and survival in northern temperate regions. Spring bud flushing was studied in a Salix pedigree (n = 82) derived from a cross between the male hybrid clone Bjorn (Salix viminalis x Salix schwerinii) and the female clone 78183 (Salix viminalis). The timing of bud flush was recorded outdoors in two consecutive years (1998, 1999) and indoor in the spring of 1998. Timing of bud flush was found to be under moderately strong genetic control (clonal mean heritabilities ranging from 0.43 to 0.72). Phenotypic correlations between height growth and bud flushing were negative but non-significant (r = 0.1-0.3). Using a Salix linkage map composed of 325 AFLP and 38 RFLP markers, six quantitative trait loci (QTLs) and three unmapped marker loci associated with timing of bud flush were detected. Four QTLs were detected in the field experiment while two QTLs and three unmapped marker loci were identified in the indoor experiment. One QTL associated with indoor bud flushing coincided with one of the QTL detected from the field data. Individual QTL explained 12-24 % of the phenotypic variance. None of the bud flush QTLs coincided with QTLs controlling height growth identified previously in the same pedigree.