IN VITRO REGENERATION AND AGRONOMIC EVALUATION OF SOMACLONES OF RICE UNDER SALINE AND THERMIC STRESS

Salinity and thermal stress adversely affect growth and development of rice plants. Therefore, there is a need to develop alternative methods to conventional breeding; in this context, somaclonal variation is a novel and important source of variability from cell cultures for plant improvement. The aim of this study was to obtain rice somaclones (Oryza sativa L.) of Tallan and Viflor cultivars, from callus induced in the scutellum of seeds and evaluate their agronomic performance, under saline and thermal stress conditions. The MS culture medium, supplemented with 5-8 mg L-1 of 2,4-diclorofenoxiacetic acid (2,4-D), induced the highest percentages of callus (greater than 10 mm in diameter). Shoot regeneration was observed in MS medium supplemented with naphthaleneacetic acid (NAA) 2 mg L-1, benzilaminopurine (BAP) 1.5 mg L-1 and kinetin (KIN) 2 mg L-1. Each shoot regenerated was considered a somaclon. Seventeen somaclones of both cultivars were evaluated and conventionally propagated plants were used as control. The results show that many somaclones of Tallan and Viflor cultivars were better than the control. The yield of Tallan cv. was higher than Viflor cv., with 3.1 t ha(-1) shell grain versus 2.2 t ha(-1), respectively. Under optimal conditions, the traditional crop of Tallan and Viflor reached yields of 9.1 and 8.9 t ha(-1), respectively. Low yields are attributed to salt stress and thermal conditions, and probably to the variability induced in the process of callus induction and plant regeneration.