The Biostimulant Potential of the Seaweeds Galaxaura oblongata and Turbenaria ornate in Improving Drought Tolerance in Rice Plant (Oryza sativa L.)

Drought stress is a major limiting factor for rice production globally. The current climatic changes have further increased the incidence and duration of droughts worldwide. On the other hand, seaweed extracts have been extensively studied as biostimulants that improve plant growth, nutrition, quality, yield, and stress tolerance of rice (Oryza sativa). Different types of seaweeds have been employed for biostimulant preparation, of which algae is most commonly used. Of particular interest were Galaxaura oblongata and Turbenaria ornate seaweeds, as biostimulants that inoculate with soil in rice plants growing under drought conditions to boost the resilience of rice to drought. The incorporation of drought-stressed-rice soil with two investigated seaweeds led to improved growth, almost regulated levels of photosynthetic pigments, compatible solutes, MDA, hydrogen peroxide, and phenolic compounds as well as flavonoids, along with notably upregulated expression of PIP1;4, PIP2;7, NCDE5, and OsMyb-R1 genes of the rice cultivars Giza 177 and Giza 179, and this enhanced the water status of rice cultivars grown under drought conditions. Furthermore, this study suggested that amending soil with investigated seaweeds enhanced nutrition and osmolyte production, ameliorated MDA, and upregulated investigated drought-responsive genes as well as promoted the growth along with antioxidant reply thoroughly contribute to improving rice plant tolerance to drought stress.