Algal amendment improved yield and grain quality of rice with alleviation of the impacts of salt stress and water stress

The hazardous effect of abiotic stress and the beneficial effect of organic amendments on rice have been extensively studied during the vegetative stage, but little information is available regarding rice yield. Therefore, the response of rice yield to abiotic stress × organic amendment interaction needs thorough investigation. The differential potency of aqueous extract and biomass of the seaweed Dictyota dichotoma in alleviation of NaCl salinity and PEG-6000 water stress, at Ψw of -0.492 MPa in medium-textured soil, on yield of cv. Sakha 101 of Oryza sativa was investigated. Grain yield, number of spikes/plant, number of grains/spike, and seed index were lowered by 59%, 47%, 40%, and 35%, respectively under salt-stress with relatively severe reductions of 63%, 50%, 50%, and 40%, respectively under water stress. Also, the improvement in grain yield, number of spikes/plant, number of grains/spike and seed index by algal amendment was greater with algal extract (106%, 72%, 79%, and 81%, respectively) than algal powder (71%, 52%, 46%, and 65%, respectively). The improved grain yield of algal-amended plants was paralleled with the production of wider, heavier and drier grains. Both salinity stress and water stress significantly reduced grain protein but increased soluble sugars and starch contents. The grain content of protein, K⁺, Ca²⁺, P and N was improved while that of Na⁺ was reduced in response to algal amendment with marginal effects on soluble sugars and starch. Rice grain vigor was positively correlated to protein and mineral nutrient contents versus negative correlation with soluble sugar and starch contents. Both algal amendment and abiotic stress agreed in reducing grain As content. The benefit afforded by Dictyota dichotoma to rice yield justifies manipulation of the algal extract for alleviation of abiotic stress on rice yield and improvement of grain quality.