Breeding for salinity tolerance in rice

Soil salinity was one of the major rice production constraints in South and Southeast Asia. The most relevant strategy was the genetic manipulation of plants to breed salt-tolerant varieties. Efforts to breed for salinity tolerance had been attempted but the progress was slow due to limited knowledge of the genetics of salt tolerance; inadequate screening and selection methods, and poor understanding of interaction of salinity and environments. Rice was moderately sensitive to salinity, threshold being EC3 dS/in beyond which yield starts decreasing. Salinity inflicted osmotic effects, ion toxicity and nutritional imbalance in rice. It affected almost all phases of growth of rice plant and decreased yield adversely. Considerable genetic variation in salt tolerance among rice varieties exists. It was thus possible to improve the genetic tolerance of rice varieties to salinity by adopting various breeding methods. In addition to conventional breeding, other innovative breeding techniques such as tissue culture, induced mutations and wide crosses needed to be explored. Inheritance studies on salinity induced panicle sterility had indicated that resistance to sterility was dominant character and presumably controlled by at least 3 pairs of genes. Uptake of Na in salt-tolerant sensitive varieties were also under genetic control. Recent studies conducted in Phytotron, greenhouse, and in field conditions indicated that seedling tolerance differs from flowering tolerance in rice varieties. Different morphological characters showed different response to salinity. Varieties also reacted differently for each character at different stages of development. Therefore, it was likely that different genes for salinity tolerance were involved at different physiological stages of development such as seedling growth, vegetative growth, and flowering