Genetic improvement of sunflower in Argentina between 1930 and 1995 - PartIII. Dry matter partitioning and grain composition

We compared the partitioning of dry matter and the oil and protein content in the grain of sunflower (Helianthus annuus L.) cultivars released in Arge ntina between 1930 and 1995. At anthesis, the fraction of plant dry matter partitioned to leaf and head increased, whereas the fraction in the stem de creased with year of cultivar release. Improved oil yield was related to th e increase in: (i) harvest index (grain mass/shoot mass) from about 0.3 to 0.5; (ii) kernel-to-grain ratio from 0.6 to 0.8; and (iii) kernel oil conce ntration from 58 to 70%. The duration of the period of grain growth as a fr action of season length accounted for half of the variation in harvest inde x. Kernel oil concentration was negatively associated with protein concentr ation which dropped from 23 to 13%. Further improvement in partitioning may be possible, including increase in harvest index resulting from enhanced c ontribution of stored assimilate to grain growth. Owing to the dramatic imp rovement in partitioning achieved in the last seven decades, however, furth er increase in yield may need to focus on increasing biomass production. (C ) 2000 Elsevier Science B.V. All rights reserved.