Field performances of rice somaclones at low temperature: Effects of callus chilling treatment

Chilling is one of the major constraints of rice (Oryza sativa L.) culture in cool environments. As an alternative to classical breeding, rice plants showing enhanced chilling tolerance in controlled environments were previously obtained from tissue culture. This study tested these 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 cultivated in a greenhouse. The R1 families (i.e., plants rising from a same RO plant) and the original parental cultivars were cultivated at 1580 m in Burundi, East Africa, from 1991 to 1992. The R2 progenies of the best-performing R1 families and parental plants were cultivated in the same conditions in 1993. For parameters concerning tillering capacity, maturity, and seed production, R2 families had lower means but higher variation (variation coefficients, minimum, and maximum values) than 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 callus stress usually resulted in the lowest performances. In contrast, the best performing Facagro families usually arose from unstressed calli. Opportunity for in vitro selection may thus depend on the original genotype.