Evaluation of indigenous wheat germplasm under NaCl salinity

Studies were carried out to (i) screen and select the indigenous wheat germplasm for tolerance to increased levels of NaCl salinity and (ii) to understand the physiological mechanism of salinity tolerance at germination. Results revealed that salinity tolerance ability of genotypes differed substantially at various growth stages. Highest EC-50 (17.95 dS m-1) was shown by 234/2 and was minimum in Fsd-83 (11.07 dS m-1) while 243/1 behaved as medium responsive (EC-50 = 16.91 dS in m-1) as compared to other genotypes at all growth stages. Remaining genotypes indicated quite variable response to salinity at different growth stages. Correlations were established between various growth and yield parameters with EC50 in order to find criteria of salt tolerance. Among the growth and yield parameters, increased number and area of green leaves, prolific root system, increased number of tillers (shoot dry weight), 100-grain weight and grain yield per plant were positively correlated with EC-50. A plausible and increased number of tillers diluted the toxic effects of ions and hence translocation to physiologically active parts was reduced. Similarly increased photosynthetic area enabled the tolerant genotypes to display greater dry matter and grain yield production under salinity. Applied salinity at the germination stage indicated a reduced rate and percentage of germination and subsequent growth. The growth and dry matter production of seedling was reduced in all the genotypes. Levels of Na+ and Cl- were increased in the plumule and redical while on the other hand, the nutrients like K+, Ca- 2+, N and P nutrients were decreased in the parts. For the study of psychological mechanism at booting stage partitioning of elements, accumulation of osmotica, some photosynthetic parameters and some anatomical characteristics were determined under control, 10, 15 and 20 dS in m-1 levels of salinity. The tolerant genotypes were able to partition the excess of toxic ions into older psychological less active parts, while beneficial elements were preferentially transported to the young leaves and roots. Among the osmotica free proline and total soluble sugars appeared to contribute significantly to the regulation of osmotic activity in younger parts even under highest level of salinity. Rate of photosynthesis, stomatal conductance and rate of transpiration were also decreased under increased levels of salinity. There was significant reduction in the chl a, chl b and total chlorophyll contents whereas chl a/b ratio increased under increased salinity. Study of anatomical characteristics of leaf of selected material revealed that the effect of NaCl was more prominent particularly on the number of stomata and stomatal size of the sensitive Var. Greatly reduced stomatal size of sensitive var. inhibited the transport of water under salinity and induced and osmotic effect which results in decrease of rate of photosynthesis and eventually reduction of dry production. Increase in salt stress caused a drastic reduction in spike length, number of spikelets per spike, number of grain per spikelets, 100-grains weight and grain yield per plant in all the three genotypes. However, tolerant genotype displayed greater matter economic yield than sensitive one. This revealed that osmotic rather than toxic component of salinity is a crippling factor in the reduced economic yield indicated by the sensitive Var. To conclude, 234/2 exhibited tolerance to salinity at all phonological growth stages and showed greater economic yield. This can be successfully grown under low to moderate level of salinity due to their physiological tendency to tolerate salinity. However problem of slightly reduced germination can be overcome by enhancing seed rate upto 25% to achieve optimum crop stand. It is expected that this information will pave the way for breeders to develop high yielding salt tolerant variety by conventional breeding and modern biotechnological techniques.