The nature of quantitative variation in a large set of early maturing sunflower test crosses

Changes in environmental conditions and the EU policy have put more emphasis on growing alternative crops in the set aside farmlands of western Europe, and sunflowers are increasingly being grown as a minor crop in the UK. However, long-term success of sunflowers as a commercial crop depends largely on the availability of early maturing, high yielding, disease resistant varieties. The present study was conducted to investigate the nature of genetic variation among the available breeding stocks that may have to be exploited to produce such cultivars. Analysis of 182 test crosses, produced by crossing 13 male sterile (CMS) lines with 14 restorer (SB) lines, has revealed that genetic variability exists for many important traits, including maturity, vigour and seed yield. Genetic differences were also detected within the male sterile and restorer groups of lines even though they were classed as early maturing. All types of gene effects, additive, dominance and epistasis, contributed to variation among the test crosses and dominance was largely unidirectional and partial. CMS and SB lines also showed some allelic complementation and the CMS exerted a modest degree of maternal control for flowering time. The test crosses were generally more vigorous and high yielding compared to their inbred parents. But they also matured significantly late, indicating that all crosses will not be suitable as potential hybrids for the UK conditions. Genotypic correlations indicated that faster growth, early flowering, high seed number and seed weight can be combined more readily in the F1 crosses.