A gene complex for annual habit in sugar beet (Beta vulgaris L)

Annual habit in sugar beet has been shown to be controlled by a dominant gene, B, which induces bolting under long days without the cold requirement usually essential for biennial cultivars. The induction of bolting by B, however, is often influenced by both environmental and genetic factors. We studied the genetic basis for bolting suppression, caused by delayed planting, in lines derived from a cross between annual and biennial lines. The F-2 progeny of a late-bolting F-1 plant yielded an unexpected segregation ratio of annuality from monogenic inheritance when planted in late May, there being an excess of non-bolting biennials, although the expected segregation was observed in the late April sowing. Bolting suppression was caused by restricted daylengths due to delayed planting because the segregation was normal under artificially induced long days. The analysis with Idh1, an isozyme marker proximal to B, demonstrated that heterozygous B plants were more susceptible to bolting suppression due to delayed planting than homozygous B plants. The results suggest that bolting suppression was controlled by a number of genes responsible for long daylength requirement, one of which was closely linked to B and formed a gene complex for annuality. The annual habit was controlled singly by B under long days but modified by the genes for long daylength requirement under restricted daylengths.