In Vitro Selection for Salt Tolerance in Maize

Abstract

An important goal in maize breeding is represented by the development of genotypes capable of maintaining competitive production yields in adverse as well as in optimal environments (Gardner and Stevens 1988; Stevens et al. 1988). Breeding maize solely for yield, in high-yielding environments, may lead to the loss of genes responsible for the buffer system of the plant toward stresses. Maize has been categorized among the crops most sensitive to salinity, and it is considered the most salt-sensitive species among cereals (Maas and Hoffmann 1977). Although maize cultivation is generally replaced in saline soils by more adapted crop systems, it would, however, be useful to explore the genetic diversity existing in maize germplasm for tolerance to salt. It is also well known that climatic and soil conditions may cause accumulation of salts also in areas in which this problem has never been encountered before (Epstein 1976). The capacity of a crop species to minimize the unfavorable effects elicited by salt is an important attribute advantageous for plant survival, development, and yield. The most relevant effect of salinity is a general growth retardation of the plant (Bernstein and Hayward 1958; Bernstein 1975). Plants like maize, in which yield is strongly linked to the vegetative dry matter production, suffer the salt effects mainly as decrease in plant size and consequent yield reduction (Bernstein 1964). Data available in literature strongly demonstrate the existence of a conspicuous genetic variability among maize genotypes in their capacity to buffer extreme conditions of the environment. The effects of salinity on some cultivars of maize grown in Pakistan have been recently investigated. The work performed on germination in the presence of NaCl, shows the existence of genetic variability for the trait of salt tolerance in the very early stages of growth (Ashraf and McNeilly 1986). The data analyzed, however, also point out that each genotype most likely displays its own independent mechanism for buffering the salt effects and that, in general, the whole plant performance in soil still gives the best selection criterion (e.g., Rush and Epstein 1981; Kingsbury and Epstein 1984).