The effect of salinity stress on growth and photosynthetic parameters of hybrid and Iranian spinach cultivars

Excessive salinity of the soil reduces the production of agricultural products, including vegetable crops, Which especially are sensitive in the vegetative parts. The salinity threshold of most vegetable crops is low (between 1 and 2.5 ds.m-1) and the salinity tolerance of vegetables decreases when saline water is used for irrigation. Choosing the right cultivar for areas with high salinity is the first management strategies for the production of high quality products. Spinach is in the group of moderately sensitive plants to salinity stress, although there are differences between various cultivars. Therefore, the present study was designed and conducted to evaluate the growth and photosynthetic characteristics of two spinach cultivars, under salinity stress and to determine the most tolerant cultivar to salinity and suitable for cultivation in saline areas.

This research was carried out factorial with two factors including three levels of stress in a completely randomized design with four replications at research farm of Vali-e-Asr University of Rafsanjan in 2018. The factors included salinity stress (at four levels 0, 10, 20, 30 mM NaCl) and cultivar (‘Barg-Pahn-e-Varamin’ and ‘NARITA’ F1 hybrid). After 45 days from the beginning of salinity treatments, plants were harvested and the parameters were measured. Characteristics such as fresh and dry weight of shoot and root, leaf area, leaf number, photosynthetic pigments (chlorophyll a, b, carotenoid), total chlorophyll, SPAD index, photosynthesis rate, transpiration rate, stomatal conductance, chlorophyll fluorescence index (Fv/Fm ratio) and photosynthesis efficiency index (PI).

The results of this study showed that the growth characteristics of both spinach cultivars such as leaf number, leaf area, fresh and dry root weights, fresh and dry shoot weight, decreased under salinity stress conditions. With increasing salinity levels, leaf area of both cultivars decreased but the leaf area of Iranian cultivar was higher than the hybrid cultivar. The results also showed that the amount of photosynthetic pigments in the Iranian cultivar was higher than the hybrid cultivar in salinity conditions. In general, total chlorophyll content decreased under salinity stress, but the amount of chlorophyll a and total chlorophyll content were higher in the Iranian cultivar. Photosynthetic indices such as photosynthesis rate (Pn), stomatal conductance (gs), transpiration rate (Tr) and chlorophyll fluorescence index (Fv/Fm ratio) decreased under salinity stress, which was different in both Iranian and hybrid cultivars. Further reduction of these parameters in stress conditions in Iranian cultivar was less than the hybrid cultivar.

Growth characteristics such as leaf area, leaf number, fresh and dry root weight, fresh and dry shoot weight of two spinach cultivars decreased in salinity conditions. The amount of photosynthetic pigments in the Iranian cultivar was higher than in the hybrid cultivar and decreased in both cultivars under salinity stress. Photosynthetic indices also decreased under salinity stress, although changes in photosynthetic indices in both cultivars were approximately the same, but the value of these parameters were higher in Iranian cultivar. In general, salinity stress reduced the growth and photosynthetic parameters of both Iranian and spinach hybrids, but the reduction in growth characteristics in the "bargpah-e Varamin" cultivar was lower than the hybrid cultivar. Therefore, it seems that the Iranian cultivar is more tolerant to salinity stress than the hybrid cultivar, and this difference in cultivars to salinity stress can be attributed to their genetic diferences.