Assessment of the Utility of Oryzaglaberrimain Breeding for Drought Tolerance In Rice

Abstract

Oryza glaberrima,the cultivated rice species that originated from West Africa is well-adapted to harsh growing ecologies of Africa. However, very few O. glaberrima accessions have been used in varietal improvement. The aim of this study was to identify promising O. glaberrima accessions tolerant to drought stress for use in breeding drought tolerant rice. Two thousand, one hundred and six accessions of O. glaberrima were obtained from the gene bank of Africa Rice Center (AfricaRice; _HYPERLINK "http://www.AfricaRice.org"_www.AfricaRice.org_). Out of these accessions, 2000 accessions were selected. The screening was conducted over a three-year period and it involved evaluating the accessions under drought and non-stress field conditions in West Africa. In the dry season of 2012, the selected 2000 O. glaberrima accessions were evaluated in an augmented experimental design in a lowland paddy field in Ibadan station. Severe drought stress was imposed during the reproductive stage and variation within O. glaberrima for drought tolerance was observed. Based on the phenotypic assessment, 200 accessions with higher grain yields and 285 accessions with higher biomass were selected. Further, 74 and 30 accessions wereselected andtested under different experiments. The best 10 drought tolerant accessions (TOG 7400, TOG 6519-A, TOG 6223, A2-123, TOG 6344, TOG 6461, TOG 6399, RAM 133, RAM 138 and TOG 12349) identified were used in interspecific breeding with O. sativarice varieties widely cultivated in Africa to develop drought tolerant rice. Eight selected O. glaberrima accessions (TOG 7400, TOG 6519-A, TOG 6520, TOG 7442-B, TOG 6223, A2-123, TOG 6344 and TOG 6461)from systematic screening showed consistently higher grain yield than O. sativachecks across the stress environments. These accessions yielded over 4 t ha-1 under drought stress and non-stress conditions. The results showed that some of the selected O. glaberrima were better in yield and some yield related traits than O. sativa under drought stress and non-stress conditions and exhibited higher drought tolerance ability than some of the prominent O. sativa cultivars. In some cases, the grain yields were at par with O. sativa. Some of these accessions were used as donor parents in interspecific breeding which produced 1,185 fertileF1 seeds. Microsatellite SSRs markers detected polymorphism among the progenies. These progenies were tested at F4 generation along with standard O. sativa checks under drought stress and non-stress conditions and the best drought tolerant interspecific lines (ART275-1-1, ART275-1-47, ART275-1-99, ART275-1-94, ART275-14-23, ART275-3-1 and ART275-9-23)were identified. These produced grain yield which ranged from 2.2 to 3.2 t ha-1. The selected O. glaberrima accessions are therefore, potential sources of drought tolerance which could be used for the improvement of O. sativarice for drought tolerance. These new donors are particularly important in Africa because of the prevalent weather uncertainties.