Mitigation of salt stress in white clover (Trifolium repens) by Azospirillum brasilense and its inoculation effect.

BACKGROUND: Salinity is one of the increasingly serious environmental problems worldwide for cultivating agricultural crops. The present study was aimed to ascertain the potential of beneficial soil bacterium Azospirillum brasilense to alleviate saline stress in Trifolium repens. Experimental plants (white clover) were grown from seeds and inoculated with or without A. brasilense bacterial strain supplemented with 0, 40, 80, or 120 mM NaCl into soil. RESULTS: The growth attributes including, shoot heights, root lengths, fresh and dry weights, leaf area and chlorophyll content were significantly enhanced in T. repens plants grown in A. brasilense inoculated soil than un-inoculated controls, particularly under elevated salinity conditions (40, 80 and 120 mM NaCl). Malondialdehyde content of leaf was recorded to be declined under saline conditions. Moreover, the K+/Na+ ratio was also improved in bacterium-inoculated plants, since A. brasilense significantly reduced the root and shoot Na+ level under high salty environment. CONCLUSIONS: Results revealed that soil inoculation with A. brasilense could significantly promote T. repens growth under both non-saline and saline environments, and this study might be extended to other vegetables and crops for the germination and growth enhancement.

Growth and Mineral Nutrition of the Chickpea ( Cicer arietinum L.)-Rhizobia Symbiosis under Water Deficit

ABSTRACT The effect of the water deficit on the fresh and dry weight in the various parts of the plant and on several mineral processes in different symbiotic combinations for the chickpea (Cicer arietinum L.) varieties was studied. The experiment was undertaken in the greenhouse during five weeks.Seedlings were separately inoculated with a suspension of three rhizobia strains and were grown under water deficit (50% of field capacity). Our results showed that the inoculation with the adequate rhizobia may improve the chickpea dry weight by improving the nodules weight, increase NR activity and more K+ accumulation under water deficit. Generally, MC0415 (S1) strain gives the best results, particularly in the dry weight nodules (5% of reduction) and in parallel higher NR activity was notedinthenodule systems (0.8±0.02 μmol NO2-g FW-1h-1) with the combination V46-S1. We note a strong correlation between the dry weights of the various parts of the plantand the studied variables (NRA, Na+, andK+).

In vitro response of date palm (Phoenix dactylifera L) to K/Na ratio under saline conditions

BACKGROUND: Salinity is a serious factor limiting the productivity of agricultural plants. One of the potential problems for plants growing under saline conditions is the inability to up take enough K+. The addition of K+ may considerably improve the salt tolerance of plants grown under salinity. It is assumed that increasing the K+ supply at the root zone can ameliorate the reduction in growth imposed by high salinity. The present study aims to determine whether an increase in the K/Na ratio in the external media would enhance the growth of date palm seedlings under in vitro saline conditions. METHODS: Date palm plants were grown at four concentrations of Na + K/Cl (mol/m³) with three different K/Na ratios. The 12 salt treatments were added to modified MS medium. The modified MS medium was further supplemented with sucrose at 30 g/l. RESULTS: Growth decreased substantially with increasing salinity. Growth expressed as shoot and root weight, enhanced significantly with certain K/Na ratios, and higher weight was maintained in the presence of equal K and Na. It is the leaf length, leaf thickness and root thickness that had significant contribution on total dry weight. Na+ contents in leaf and root increased significantly increased with increasing salinity but substantial decreases in Na+ contents were observed in the leaf and root with certain K/Na ratios. This could be attributed to the presence of a high K+ concentration in the media. The internal Na+ concentration was higher in the roots in all treatments, which might indicate a mechanism excluding Na+ from the leaves and its retention in the roots. K/Na ratios up to one significantly increased the leaf and root K+ concentration, and it was most pronounced in leaves. The K+ contents in leaf and root was not proportional to the K+ increase in the media, showing a high affinity for K+ uptake at lower external K+ concentrations, but this mechanism continues to operate even with high external Na+ concentrations. CONCLUSION: Increasing K/Na ratios in the growing media of date plam significantly reduced the absorption of Na+ less than 200 mM and also balance ions compartmentalization.