Contribution of pre-anthesis photoassimilates to grain yield: Its relationship with yield in Argentine sunflower cultivars released between 1930 and 1995

Published analyses of the changes in yield potential of the sunflower crop in Argentina across cultivars released between 1930 and 1995 suggested that part of the observed increase in yield potential could have arisen from a larger contribution from non-structural carbohydrates (NSC) present in the crop at anthesis. To test this idea, stems and receptacles were harvested at intervals over the anthesis-post-physiological maturity phase from crops, grown under good water and nutrient availability conditions, of three open-pollinated (OP) cultivars and five hybrids released at various times between 1930 and 1995. Stem NSC and structural biomass (SB) at anthesis diminished in the hybrids as compared with the OP cultivars (and across year of cultivar release), in spite of the fact that some hybrids had a significantly greater (p <0.05) stem NSC concentration at anthesis. By contrast, receptacle SB and NSC concentration at anthesis showed no sign of change with year of release. Stem NSC content fell from early grain filling or from anthesis in all cultivars while receptacle NSC content rose and then fell during grain filling in most cultivars. In five of the cultivars examined, receptacle NSC content was greater at physiological maturity than at anthesis. Crop and organ NSC content dynamics varied across cultivars, in association with variations in cultivar stem biomass at anthesis, stem NSC concentration at anthesis, and cultivar particularities in post-anthesis NSC accumulation. Cultivar differences in changes of crop NSC content between anthesis and physiological maturity (ΔNSCA₋PM, +37.7 to -55.7gm-²) were also found, and these changed with year of cultivar release in each of the OP and hybrid categories, tending toward a null variation of ΔNSCA₋PM in the most recent releases of both groups of cultivars. In each of these two groups of cultivars, ΔNSCA₋PM also diminished with crop growth rate during grain filling, a variable that showed a strong (r ² =0.65) linear relationship with yield corrected for oil synthesis costs. The value of ΔNSCA₋PM as an additional (to crop growth rate during grain filling) explanatory variable for yield corrected for oil synthesis costs, was non-significant. We conclude that, under conditions of ample water and nutrient availability, there is no evidence that cultivar differences in NSC economy during grain filling had an important role in breeding for greater sunflower yield in Argentina over the cultivar release period 1930-1995.