Seed yield and associated trait improvements in sunflower cultivars over four decades of breeding in South Africa
Genetic improvementfor seed yield and oil-contentin sunflower cultivars was initiated in the early 1970s in South Africa. Since then no study has been carried out to assess the progress and contribution of new cultivars to seed yield improvement to justify continued investment into breeding new cultivars. The aim of this study was therefore to quantify the contribution of new cultivars to seed yield and associated traits in sunflower over four decades of breeding in South Africa. Two data-sets were used in this study: (1) side-by-side evaluation of historical and current sets of popular cultivars in the same environment under one set of trial management practices; and (2) yield trends in commercial farmers’ fields based on annual production estimates. The absolute genetic gain (yield increase per year) for seed yield in the side-by-side trials ranged from 18 to 32 kg ha−1 year−1 with a mean of 24 kg ha−1 year−1. In contrast, the absolute seed yield increase under commercial production was 12 kg ha−1 year−1. The estimated relative genetic gain for seed yield based on side-by-side trials was 1.5% year−1 and the relative gain in seed yield per year under commercial production was 1.9% year−1. The contribution of new cultivars to total seed yield progress in sunflower were 56.3% for the period 1970–1989; 23.9% from 1990 to 2009 and the mean over the four decades under consideration 1970–2009 was 41.6%. Positive increases in genetic gains for oil yield, oil content and number of seeds per head were also obtained although the gain in oil content was relatively low.