Sporophytic and gametophytic recurrent selection for improvement of partial resistance to Alternaria leaf blight in sunflower (Helianthus annuus L.)

Alternaria leaf blight, caused by Alternaria helianthi Hanf., is one of the most important diseases of sunflower causing significant yield losses in several tropical countries. Yet, so far, only partial resistance for the disease has been discovered in the germplasm through conventional sporophytic selection. Therefore, the main objective of the present investigation was to compare sporophytic and gametophytic recurrent selection with the aim to enhance the level of resistance to Alternaria leaf blight. The base population was synthesized by random mating three populations- two interspecific derivatives involving different species of Helianthus and one germplasm accession based on their partial resistance to disease incidence. The base population was subjected to 1-2 cycles of both sporophytic and gametophytic selection. The gametophytic selection was practiced by applying pathogen culture filtrate to the stigma and style one hour before pollination. The selection response was measured by scoring the percent disease index at flowering, 15 days after flowering, and at physiological maturity and by quantifying economic yield gain. A significant reduction in mean per cent disease index values and a gain in seed yield were observed for both the types of selection cycles, but more so for gametophytic selection. The populations improved through gametophytic selection appear to be more promising as the pollen selection allowed the selection of rare favorable allelic combinations that would hardly be detected at the sporophytic level. A combination of gametophytic selection and conventional sporophytic selection should be considered as an effective tool in population improvement programs to achieve higher levels of resistance in relatively short time.