Seed filling patterns of safflower: Genotypic and seasonal variations and association with other agronomic traits

Safflower (Carthamus tinctorius L.) plants grown under Mediterranean environments are subjected to several biotic and abiotic stresses during the seed filling period that limit their production. The genotypic and seasonal variation in seed filling parameters and their association with agronomic traits were investigated in field experiments conducted for 2 years. A set of 10 safflower genotypes, which included hybrids and open pollinated varieties, was used. Seed filling rate (mg head−1 day−1) and duration (days) were calculated by using the cubic polynomial model. Data obtained indicated that this model could be successfully used to simulate the seed growth and to estimate the seed filling parameters in safflower genotypes with high coefficients of determination (r2) that ranged from 0.901 to 0.999. Seasonal differences were observed only for seed filling duration that was mainly determined by the sink size, as it was specified by the number of seeds per head. Greater sink size induced by higher head fertility (number of seeds per head) resulted in a longer seed filling duration. Genotypes differed greatly in seed filling rate. Seed yield and seed oil yield were significantly correlated with seed filling rate. More than 57% of the variation among genotypes in seed yield was due to the corresponding variation in seed filling rate. Increased seed filling rate improved dry matter partitioning to the seeds contributing to a higher harvest index. Results indicate that selection of genotypes with high seed filling rate could be a successful strategy to increase production of safflower grown under Mediterranean environments.