Yield in the rainfed rice ecology of West Africa is held back by a number of biotic and abiotic stresses, drought being one of the most significant. Drought years have been increasingly frequent. The breeding program of the Africa Rice Centre (WARDA) for rainfed rice has been exploring resistance to production stresses found in the gene pool of African rice (O. glaberrima). Exploitation of this gene pool is now under way to develop drought-tolerant varieties, using in particular O. glaberrima accessions collected in Mali and introduced interspecifics.

In the 2004 dry season at Samanko Research Station in Mali, 211 genotypes were evaluated for reaction to drought stress at the vegetative stage in three alpha-lattice trials (A, B, C), each of 80 treatments, in three replications. The test genotypes comprised the following four groups: 1) 108 Oryza glaberrima accessions collected in Mali, 2) and 3) 96 interspecific lines (derived from O. glaberrima x O. sativa crosses) from the International Center for Tropical Agriculture (CIAT) and 9 from WARDA, and 4) 8 O. sativa landraces from WARDA’s Genetic Resources Unit. The genotypes were first irrigated then later irrigation was withheld. Seedling vigour, drought-stress characters and drought recovery were all rated two or more times using the evaluation scale of the International Rice Research Institute (IRRI).

Significant (p £ 0.05) differences were evident between genotypes for all characters except seedling vigour in trials A and B, the first rating for leaf rolling in trial B, and the second drought-recovery rating in trial C. In trial C, 6 lines exhibited significantly better seedling vigour than Nerica 1 at the first rating and 13 at the second rating. Five of the lines were common to both ratings.

Among the drought-stress characters rated, only two lines, RAM 55 and RAM 72 (O. glaberrima accessions from Mali) in trial A, were significantly superior to Nerica 1; the former exhibited significantly less leaf rolling and better drought recovery and the latter significantly better drought recovery. However, many lines did not differ significantly from Nerica 1 for the drought-stress characters rated—leaf rolling and drying of leaf tips.

Considering the two larger groups of genotypes, the interspecific lines from CIAT and the glaberrimas from Mali, 51% of the interspecifics compared with only 17% of the glaberrimas had drought-stress ratings equivalent to Nerica 1. The interspecifics showed better mean drought-stress ratings for five of the seven characters rated. The mean of the glaberrima accessions was only marginally superior to the interspecifics for drought stress and drought recovery. The glaberrimas, however, had a greater phenotypic range for six of the seven characters.

In trials A and C better drought tolerance was significantly correlated with less vigorous seedling growth; faster recovery from drought was significantly correlated with reduced leaf rolling and in trials A, B and C with less drying of leaf tips. Among the drought-stress characters, reduced leaf rolling was significantly correlated with less leaf tip drying.