Physiological investigations of the response of wheat (Triticum aestivum L.) to soil salinity

Abstract

A series of greenhouse and control environment experiments were carried out to study the response of some wheat cultivars (Triticum aestivum L. ) to soil salinity. The rate and percentage of seed germination were reduced by increasing soil salinity. The cultivar Falchetto was more tolerant in terms of germination than the other cultivars under saline conditions. Increasing salinity consistently reduced the growth and dry matter production of all wheat cultivars used. The most sensitive growth character to salinity was leaf area and tiller number while net assimilation rate was least sensitive and sometimes not affected by salinity. The retardation of growth under salt stress in this study may result from reduced leaf area for photosynthesis, but the cause of reduced leaf area is not clear. In all cultivars tested, grain yield and its components were reduced by increasing soil salinity (0 - 0.6% salt) or irrigation with saline water (0 - 4000 ppm salt). The most sensitive yield characters to salinity were spike number and grain number per spike while spike length and spikelet number per spike were less sensitive as compared with the other components. Falchetto and Shakha 62 were less sensitive than the other cultivars used in this study. Leaf proline content increased while leaf chlorophyll content decreased with increasing soil salinity. Also, leaf and stem content of sodium, calcium and magnesium increased with increasing salinity levels both in vegetative parts and in grains. Increasing soil salinity increased ash and protein content of wheat grains but decreased moisture and total carbohydrate content. Application of nitrogen fertilizer under saline conditions enhanced grain yield and its components and to some extent countered the adverse effect of soil salinity up to 0.4%. While added nitrogen did not increase growth and dry weight of wheat plant significantly, crop growth rate increased significantly. On the other hand spraying wheat crop with trace elements did not affect the growth and grain yield and its components except 1000 kernel weight under saline conditions. The interaction effect between salinity and some environmental factors was significant on germination and growth. Under saline and non-saline conditions increasing temperature from 10 to 20°C increased germination capacity and depressed it between 20 and 30°C. Also, increased relative humidity from 47 to 92% increased germination capacity. For vegetative growth, generally, increasing temperature up to 20°C, relative humidity from 47 to 92%, and available soil water content from 20 to 100% increased vegetative growth and dry matter production of wheat plant under saline and non-saline conditions. The interaction effect between salinity and presoaking with plant growth regulators (CCC, GA3, IAA and Kinetin) and salt solutions (Nacl and Cacl2 ) on germination and growth of wheat accelerated germination under saline and non-saline conditions. For some characters presoaking with these plant growth regulators or salt reduced the deleterious effect of salinity and improved plant performance at these early stages of growth under saline conditions. Water and osmotic potentials, total and relative water content (RWC) and transpiration rate decreased and stomatal number per microscope field increased with increasing soil salinity, but turgor potential was essentially unchanged by increasing soil salinity indicating osmotic adjustment. Also, it is evident from the water relations, PEG and RH experiments that ion toxicity effect operated in addition to the osmotic one during early stages of growth