FIELD PERFORMANCES OF RICE SOMACLONES AT LOW-TEMPERATURE - EFFECTS OFCALLUS CHILLING TREATMENT

Chilling is one of tile major constraints of rice (Oryza sativa L.) cu lture in cool environments. As an alternative to classical breeding, r ice plants showing enhanced chilling tolerance in controlled environme nts were previously obtained from tissue culture. This study tested th ese plants in the field under a cool climate. Calli of four cultivars adapted to high altitude ('Facagro 57', 'Facagro 76', 'Kirundo 3', and 'Kirundo 9') were cultivated either at 4 degrees C (during 2, 4, or 6 wk, continuously or not) or at 25 degrees C. R0 plants (i.e., plants regenerated from calli) were then regenerated at 25 degrees C and cult ivated in a greenhouse. The R1 families (i.e., plants rising from a sa me RO plant) and the original parental cultivars were cultivated at 15 80 m in Burundi, East Africa, from 1991 to 1992. The R2 progenies of t he best-performing R1 families and parental plants were cultivated in the same conditions in 1993. For parameters concerning tillering capac ity, maturity, and seed production, R2 families had lower means but hi gher variation (variation coefficients, minimum, and maximum values) t han the parental plants. Differences appeared between callus chilling treatments. In the Kirundo cultivars, the longest chilling treatments led to the best performing families for most parameters, while no call us stress usually resulted in the lowest performances. In contrast, th e best performing Facagro families usually arose from unstressed calli . Opportunity for in vitro selection may thus depend on the original g enotype.