Abstract

Rice production is usually reduced by water stress that can evenly occur during rice cycle in West Africa under bimodal rainfall pattern. In order to determine the effects of water stress on rice grain quality, experiments were conducted on upland site (on ferralsol) at the main AfricaRice research center at M’be, 30 km North of Bouaké, Côte d’Ivoire. The rice varieties CG14 (Oryza glaberrima), WAB56-104 (Oryza sativa), and NERICA1 (cross WAB56-104 x CG14) were sown at 25 × 25 cm spacing during the dry season cropping period of 2000, 2001 and 2002. Irrigation line (Boon irrigation) was used to supply water until flowering stage. Water was then supply manually from the milky stage of each variety to its full ripening stage. Physical (husking yield, milling recovery, and head rice ratio), chemical (amylose and proteins contents) and cooking parameters (cooking time, volume expansion, rice flour gelatinization temperature, consistency and viscosity) of the harvested grains were determined in the laboratory. The results showed a significant difference (p < 0.05) between all the parameters in comparison with the checks samples and stressed crop. In general, NERICA 1 showed better physical and cooking quality traits than its parents. Rice samples from plots subject to lower water availability during repining stage showed higher protein content for all varieties studied. Increase in the average protein content of stressed samples were 31, 11.8 and 13.3% times, respectively for NERICA 1, CG14 and WAB56 -104, where (using the protein content of check plots as 100%) NERICA 1 showed higher husking yield, total mean milling recovery and head rice ratio for samples collected on stressed plots than the glaberrima and thesativa samples recorded on similar plots. Finding showed that cooking properties that meet West African rice consumers’ preferences for cooked rice were more improved for NERICA 1 than its parents in comparison with samples collected from stressed plots. It is concluded that moisture stress at ripening stage should be further investigated as potential indirect means of improving rice grain quality.

Key words: Interspecific, grain quality, water stress, Oryza glaberrima, Oryza sativa.