Plant Breeding for Salt Resistance
Salt tolerance refers to the ability of plants to prevent reduce or overcome the injurious effect of soluble salts present in their root zone. The problem of salinity is of global significance because saline and alkaline soils are found in almost all countries of the world. In India, more than seven million hectares land is estimated to be salt affected. Higher concentration of salt in the soil adversely affect the growth and development of plants by disturbing various physiological processes.
There are two ways to overcome the problem of salinity. One is reclaim the salt affected soil and the other is to develop salt tolerant genotypes/ cultivars. The first method is very costly, time consuming and short method, on the other hand, is long lasting, more effective and less costly. Genetic differences exist among cultivars for their salt tolerance capacity, moreover, plants adapt themselves to adverse environments for their survival. High salt tolerant plants in crop are found in the salt affected areas.
Breeding Approaches:
In India, breeding work for salt resistance is carried out at Central Soil Salinity Research Institute (CSSRI), kernel and its various regional centres. In India, two types of approaches are followed for salt tolerance breeding. The two approaches are:
1) Improving yield level of salt tolerant cultivars, and 2) Transfer of salt tolerant genes to high yielding cultivars. In the first traditional cultivars of salt affected areas are improved for their productivity without affecting their salt tolerance ability. In the second approach, salt tolerances gene from locally adapted ( Salt tolerant) cultivars are transferred to high yielding cultivars through hybridization and selections.
Screening Techniques:
Various methods are used for screening segregating material for salt resistance. The commonly used methods are: 1) Lysimeter micro plots, 2) Sand culture, and 3) Solution culture tanks. The Lysimeter micro plots of 6 m X 3 m X 1 I size are used at CSSRI, Karnal. Several levels of salinity are used and replicated experiments are conducted to screen for salt resistance. Some workers prefer to use sand culture technique using nutrient solution. Solutions of various salinity levels are applied in the sand. Another technique is use of solution culture tanks with several levels of salinity. Replicated experiments are conducted over seasons to get more reliable result. Genotypes which survive under salinity conditions are considered as tolerant and screened further.
The salt tolerance capacity differs from species to species. For example, crops like barley, cotton, sugarcane, oilseeds and grasses are known to be more salt tolerant than other crops. The salt tolerance capacity also differs within a crop based on ploidy level. For instance, in wheat, hexaploid bread wheat is more tolerant to salt than durum (tetraploid) and einkorn (diploid) wheat. In Brassica, tetraploid species are more tolerant than diploids. In rice, late maturing, tall and coarse grain varieties exhibit maximum tolerance to salinity conditions. In crested wheat grass , selection for tolerance under artificial salinity conditions improved the salt tolerance level of selected lines. In sugarcane, vast differences for salt tolerance are observed among strains. In Hawaii, salt shock treatment is used for improving salinity tolerance. In sugarcane, moreover, land races are more tolerant to salinity than high yielding cultivars.
Breeders require close cooperation of geneticist, physiologist, biochemist, and soil scientist in developing salinity resistant varieties. The new approaches such as tissue culture and genetic engineering may be rewarding in developing more salt tolerant genotypes. The main limitations in the breeding for salt tolerance are: 1) Lack of efficient selection criteria, 2) Lack of inter disciplinary cooperation, and 3) paucity of funds, etc.