Physiological approaches to improving harvest index and productivity in sunflower

Factors associated with variation in harvest index and approaches to improve harvest index (HI) and productivity in sunflower are discussed in this article. In recent years, higher productivity in sunflower has been achieved mainly through increased crop growth rates. Besides, an improvement in harvest index also has contributed for improved productivity to a certain extent. In our study we observed that medium duration types (100 to 110 days) had high HI compared with early or long-duration varieties and we also attempted to understand the ways and means to improve HI in sunflower types with varied duration. Genotypes which had low partitioning of dry matter to stem plus thalamus had high HI. Genotypes which accumulated high biomass during post flowering stages of development also showed high HI and seed yield. In a few genotypes remobilization of photosynthates from vegetative plant parts to the seed resulted in high HI and seed yield. Among the sink characters, the number of seed per head, test weight and seed density (weight/volume) also contributed to achieving high HI values. Identification and selection of genotypes based on these criteria will increase the production further. Since large amount of biomass is still locked up in the vegetative plant parts, any practice to manipulate the mobilization of photosynthates from vegetative parts to head also improves HI and thus seed yield. In our experiment, we observed that foliar application of boron nutrient and application of growth regulators to the head improved the translocation of photosynthates to the head and thus increased the HI and seed yield