Response to divergent selection for early vigour in sunflower (Helianthus annuus L.)

Abstract

Early vigour (EV), biomass at the first development stages, may be a positive trait to improve sunflower yield in water-limited environments. Field experiments were carried out from 1992 to 1995 to define an index to quantify EV in sunflower plants, evaluate the response to divergent selection for this trait, study EV ×environment interaction, estimate the heritability of EV, and study the association of EV with other traits. A sunflower population with a broad genetic base and 10 sunflower lines derived from it were used. Stem volume calculated from stem diameter and height measured approximately 425 degree-days after emergence was correlated with above-ground plant biomass at the same date. In 1992, divergent selection for high and low stem volume was carried out on this population and plants from every group were recombined independently, obtaining 2 new populations. Selection response, using these and the initial population, was studied in 1993. Ten S2 lines, 5 with high-EV derived from the high-EV population and 5 with low-EV derived from the low EV population, were sown in 1995 to study the EV ×environment interaction. Differences among lines with different EV were significant in all the environments studied. In 1993, a random sample from the initial population was selfed and broad sense heritability and heritability by parent-offspring regression were estimated. Heritability based on variance component estimates of S₁ progeny means was 0·61. Realised heritability (± s.e.) from a divergent selection for high and low stem volume were 0·40±0·10 and 0·52±0·15, respectively. Heritability by parent-offspring regression was 0· 40± 0·10. These values and the high variability of stem volume observed in the new populations indicate that additional gain from selection should be possible.