الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
SUMMARY AND CONCLUSION
Salinity of soil and/or water represents a serious threat to agricultural crop production and ecosystems worldwide, especially in dry regions. With increasing future demand for more arable lands across the world due to an ever-increasing population, salt-affected marginal lands may provide an alternative natural resource for the utilization of salt-resistant species “halophytes” using alternative water resources such as brackish or even saline water. Chenopodium quinoa Willd. (Amarantheaceae) seems to be a reliable non-conventional crop to sustain the food supply, particularly at marginal salt-prone areas, owing to its extraordinary high salt resistance and its excellent nutritional quality. Realistically, a prerequisite for the sustainable utilization of this species as a cash crop is precise information about its ecophysiological responses (various resistance mechanisms) to high salinity stress. Hence, a major motivation of the present study was to evaluate and compare the responses of three C. quinoa cultivars with variable salt resistance to different water salinity to determine the salt resistance threshold and to elucidate the individual morphological, physiological and biochemical mechanisms conferring differences in salt resistance in these closely related cultivars. Plants of C. quinoa cv. “Hualhuas”, C. quinoa cv. “Real” and C. quinoa cv. “CICA” were grown in sandy soil quick check systems (pot experiment), where they exposed to various water salinity levels (0, 100, 200, 300, 400 and 500 mM NaCl) in the greenhouse for a total period of 6 weeks. Under control conditions, plant growth and biomass production of C. quinoa differed greatly between cultivars tested. Both “Hualhuas” and “Real” cultivars had distinctly lower biomass production, with plant fresh weight averaged 112.4 and 118.5 g/plant, respectively, while “CICA” cultivar exhibited relatively higher plant fresh weight, being 179.0 g/plant. Raising water salinity led to a substantial growth reduction in all cultivars under the evaluation. The Peruvian cultivars “Hualhuas” and “CICA” were least affected by high salinity treatments, exhibiting growth reduction of about 79% and 76% respectively, while the Salares ecotype “Real” was most sensitive, with biomass reduction of about 87% relative to the controls. Interestingly, plants of all screened cultivars could complete their life cycle even at this salinity level, confirming the halophytic nature of C. quinoa. Salinity resistance threshold was at salinity level of 10, 10-20 and 30 dS m-1 for the cultivar “Hualhuas”, “Real” and “CICA”, respectively, whereas the C50 value was at salinity of 30 dS m-1 for the cultivar “Hualhuas”, at 10 – 20 dS m-1 for the “Real” plants, and at 20 – 30 dS m-1 for “CICA” plants. Taken together, the relative declines in plant biomass, C50 and the salinity resistance threshold indicate that the Peruvian cultivars “Hualhuas” was the most salt resistant cultivar, while “Real” was the most salt sensitive one, in terms of biomass production under severe salinity. The plants of all cultivars lowered their osmotic potential in all organs below that of the soil, the response that was more obvious for “Real” and “CICA” (more sensitive cultivars). Salt-induced reduction in osmotic potential is attributed to substantial accumulation in Na+ in all organs of all cultivars, although “Hualhuas” plants showed distinctly the lowest Na+ content. Consequently, K+/Na+ ratio was significantly reduced in all plant organs in response to increasing water salinity level, except for the root of “Hualhuas” plants, where this ratio was surprisingly increased. Additionally, salt-mediated reduction in K+/Na+ ratio was lowest in “Hualhuas” plants, suggesting that plants of this cultivar had a more efficient control mechanism on xylem Na+ loading and better K+ retention compared to “Real” and “CICA” cultivars under saline conditions. Raising water salinity decreased notably the content of the total soluble carbohydrates (TSC) in all quinoa cultivars under the evaluation, with more severe effects in “Hualhaus” plants. In contrary, proline was found to accumulate in all organs of the Peruvian cultivars “Hualhaus” and “CICA”. Net CO2 assimilation rate (Anet) was significantly reduced as salinity rose, reached only 22.4, 36.2 and 1.7% of the control values in “Hualhaus”, “Real” and “CICA”, respectively, at high salinity level. This was accompanied by significant decreases in stomatal conductance (gs), transpiration rates (E), but also with improved photosynthetic water use efficiency (PWUE). Interestingly, “Hualhuas” plants (most salt resistant) showed clearly the lowest gs and E, but the highest PWUE at full-strength salinity treatment, indicative of an efficient control mechanism over the stomatal aperture and hence the overall gas-exchange capacity. Together these findings allow for the speculation that the cultivar “Hualhuas” is a promising candidate with high potentials in terms of salt resistance and biomass production (can be cultivated using saline water up to 60% sws) compared to “Real” and “CICA”.