New oilseed rape (Brassica napus) hybrids with high levels of heterosis for seed yield under nutrient-poor conditions

Winter oilseed rape (Brassica napus L.) is the most important oil crop in Europe. Due to a continually increasing demand for rapeseed oil for food and non-food uses, the production of hybrid cultivars with higher seed and oil yields has become increasingly important in recent years. However, the systematic use of heterosis for hybrid breeding in oilseed rape is limited by the relatively narrow genetic basis of adapted germplasm, which can impede the generation of distinct heterotic pools. In the present study experimental hybrids were developed from a population of 190 DH lines derived from a cross between an elite, double-low seed quality (zero erucic acid, low glucosinolate content) winter oilseed rape variety and a semi-synthetic line derived from a genetically diverse resynthesised rapeseed line with high erucic acid and glucosinolate contents. The DH lines were crossed with a male sterile tester and the resulting test hybrids were examined for yield performance at two locations in Hesse, Germany, that exhibit extreme differences in climatic conditions and soil characteristics. Mid-parent heterosis for seed yield was determined at both the agronomically optimal location Rauischholzhausen and the marginal site Niederhorlen. A value of up to 43% mid-parent heterosis for seed yield could be observed among selected test hybrids compared to that of their parental DH lines. The heterosis level for yield was particularly high at the nutrient-poor site, where the best test hybrids showed significantly higher yields than elite open-pollinating and hybrid varieties. This demonstrates the suitability and adaptability of highly heterotic rapeseed hybrids on marginal locations and suggests the existence of a strong heterotic effect on nutrient uptake efficiency.