Effects of planting date, genotype, and their interactions on sunflower yield: II. Components of oil yield

Sunflower (Helianthus annuus L.) yields are strongly reduced by late sowing dates. The objectives of this study were to investigate the physiological bases of the sowing date (S), genotype (G), and genotype X sowing date (G X S) interaction effects on sunflower yield and contribute to development of ideotype-based selection strategies for improving yield at late plantings. Nine differentially adapted hybrids were evaluated during two seasons at normal and late planting dates at Venado Tuerto, Argentina, by means of the framework that defines oil yield as the product of grain number and weight and oil concentration. Sowing date was the major source of variation for oil yield. The G x S interaction, in turn, accounted for a portion of the total variability four times higher than the contribution of G. The S and G X S interaction effects on grain number were mostly determined by grain set in the central portion of the capitulum. Duration of grain filling was the main determinant of the S and G X S interaction effects on grain weight and grain oil concentration. Variation in grain oil concentration between sowing dates was largely due to changes in kernel oil proportion, rather than changes in kernel percentage. Relative changes in rate of grain filling and kernel percentage also contributed to the observed G x S interactions for grain weight and oil concentration, respectively. Although some degree of compensation among oil yield components underlie the observed G X S interactions, it was found that seed set in the central portion of the head can be used as an indicator of adaptation to late planting dates.