USE OF SOMACLONAL VARIATION AND IN-VITRO SELECTION FOR CHILLING TOLERANCE IMPROVEMENT IN RICE

Embryo-derived calli of four rice varieties cultivated at high altitud e in Burundi - Facagro 57, Facagro 76, Kirundo 3 and Kirundo 9 - were submitted to different temperature regimes. The percentage of regenera ting calli greatly varied depending on variety, length of culture and callus temperature treatment. The reduction of regeneration percentage s induced by low temperature was more pronounced in the more sensitive varieties. Regenerated plants (RO) and their progenies in R1, R2 and R3 were cold-screened together with control plants. In all varieties, significantly higher survival rates were obtained in R3 with in vitro plants than with control plants. Such chilling tolerance improvement w as not obtained following a massal selection applied during 3 successi ve generations onto the control plants. In vitro plants regenerated fr om calli cultivated either at 25 degrees C, either at 4 degrees C, wer e cultivated at different altitudes in Burundi during two successive g enerations. For most observed traits, the in vitro plants were charact erized by lower means, larger variation and higher maximum values than the control plants. The most chilling-tolerant somaclonal families we re most usually characterized by extensive differences in fatty acid c omposition, chilling-induced electrolyte leakage and chlorophyll fluor escence, compared to the varieties they derived from.