ADAPTABILITY OF IRRIGATED RICE TO TEMPERATURE CHANGE IN SAHELIAN ENVIRONMENTS

To assess genotype adaptability to variable environments, we evaluated five irrigated rice genotypes, three new varieties, WAS 161, a NERICA, IR32307 and ITA344, and two controls: Sahel 108, the most popular short-duration variety in the region, and IR64. In a field experiment conducted at two locations, Ndiaye and Fanaye, along the Senegal River, rice was sown on 15 consecutive dates at one month intervals starting in February 2006. Yield (0-12.2 t ha(-1)) and crop cycle duration (117-190 days) varied with sowing date, genotype and site. Rice yield was very sensitive to sowing date and the associated temperature regimes. Spikelet sterility due to cold stress (T < 20 degrees C) was observed when the crops were sown in August (Ndiaye), September (Ndiaye and Fanaye) and October (Ndiaye and Fanaye), and heat stress (T > 35 degrees C) resulted in spikelet sterility when sowing took place in April (Ndiaye and Fanaye) and May (Fanaye). For all experiments the source and sink balance was quantified and showed that yield was most limited by sink size when sowing between July and October. Variety WAS 161 was least affected by genotype x environment interactions, resulting in lower interactive principal component values. An increase in minimum temperature of 3 degrees C could decrease spikelet sterility from 100 to 45%. These changes in temperature are likely to force rice farmers in the Senegal River to adjust the cropping calendar, e.g. to delay planting or to use heat-tolerant genotypes.