Genetic improvement of sunflower in Argentina between 1930 and 1995: II. Phenological development, growth and source–sink relationship

Abstract

Historic sets of sunflower ( Helianthus annuus L.) cultivars released in Argentina between 1930 and 1995 were compared in two field experiments. Breeding and selection shortened cycle length: most of the reduction came from a reduction in time to anthesis, which together with a stable time from anthesis to maturity increased the proportion of the growing cycle given to grain growth. Shoot biomass at maturity was unrelated to year of cultivar release but a greater portion was produced after anthesis. The ratio between leaf area index duration from anthesis to maturity and grain number was taken as a measure of source-to-sink ratio; this ratio was smaller in hybrids than in open-pollinated cultivars. Variation in both the amount of oil per grain and grain mass were small in comparison with the variation in source-to-sink ratio indicating that additional carbon may have attenuated the effects of less leaf area duration per grain. Owing to the relative stability of the amount of oil per grain and the reduction in grain mass, the grain oil concentration increased despite the drop in source relative to sink. Further yield improvement will mostly depend upon the increase in the supply of substrates to fill the grain provided grain size is not restricted by events occurring before anthesis.