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.

The aqueous extract and powder of the brown alga Dictyota dichotoma (Hudson) differentially alleviate the impact of abiotic stress on rice (Oryza sativa L.).

Algal supplements can improve crop productivity and afford protection against abiotic stress by virtue of their rich content of plant nutrients and bioactive compounds. The present work investigates the relative efficiency of the biomass and extract of the brown alga Dictyota dichotoma in protection of rice against salinity and water stress. Rice (Oryza sativa L.) cv. Sakha 101 was grown on a silty clay soil amended with the aqueous extract and powder of D. dichotoma under NaCl and PEG 6000 stress at water potential of - 0.492 MPa. Abiotic stress, particularly water stress, reduced rice growth and concentrations of K+ and protein but increased soluble sugars, starch, proline and Na+ concentrations of plant tissues, with counterbalancing effect of algal amendment. The benefit of algal amendment was greater for algal extract than algal powder and under water stress than salt stress. Algal amendment and abiotic stress promoted catalase and peroxidase activities in rice leaves with variable effect on polyphenol oxidase. The benefit of D. dichotoma to rice can be related to macro- and micro-nutrients, growth hormones, phenolics, flavonoids, sterols, vitamins and fucoidan. The production of toxic intermediates as a result of fermentation of the algal biomass in the paddy soil might reduce the benefit of algal amendment. Although rice is salt-sensitive, it is more resistant to salt stress than to drought stress. The ability of rice to retain Na+ in the root is pivotal for stress resistance, but the role of K+ partitioning is less evident.