Role of heterosis for photosynthetic traits and sink organs in seed yield enhancement in safflower

Genetic basis of heterosis has been exploited for yield improvement in safflower (Carthamus tinctorius L.) but little is known about physiological basis of heterosis for yield. The objective of this study was to quantify the physiological basis of heterosis for seed yield in safflower by examining 19 safflower hybrids and their parents for photosynthetic traits, and yield and its components. The results showed that heterosis for yield and its components was high and positive but was low and negative for photosynthetic traits in most of the hybrids studied. There were weak and non-significant relations between photosynthetic traits and yield and its components. Hybrids were more efficient in translocating photoassimilates to two major sink organs viz., number of seeds and number of capitula despite having low net photosynthesis than parents. Seed yield increase in safflower is more sink-than source-limited and was necessary through heterosis for sink organs. Heterosis breeding for larger sink size with parallel increase in effectiveness of sink organs in translocation of photo-assimilates is suggested for yield improvement in safflower.