Drought Stress Decreases Morphophysiological Characteristics of Pongamia pinnata (L.) Pierre a Biodiesel Tree.

<b>Background and Objective:</b> Drought stress is a condition of water shortage in plants. One tree species targeted for planting on marginal lands is <i>Pongamia pinnata</i> which produces oil for biodiesel feedstock. The aims of the present study were to evaluate the morphophysiological response of <i>Pongamia pinnata</i> and its resistance mechanism under drought stress at the seedling stage. <b>Materials and Methods:</b> Three months old Pongamia seedlings were given 4 treatments of watering intervals, namely every day (control) and every 7th, 14th and 21st day at field capacity indicating no stress, moderate stress, high stress and very high stress, respectively. Measurement of growth parameters was carried out every month for 4 months. Data were analyzed using one-way analysis of variance at a significance level of 5%. <b>Results:</b> Very high drought stress reduced plant survival to 60% at 3 MAP (month after planting) and dead at 4 MAP. Both moderate and high drought stresses slow down height growth. Both specific leaf area and leaf area ratio decreased dramatically by 45.7 and 63.74%, respectively at a very high drought stress treatment at 3 MAP. Root length decreased slightly by 18.40% at very high drought stress. Total plant dry weight decreased by 15.9 and 46.4% by high and very high drought stress respectively. Leaf pigment content decreased sharply to very high drought stress. <b>Conclusion:</b> Pongamia seedlings survived under moderate and high drought stress. This was achieved by reducing plant height, leaf area, dry weights and pigment content. The resistance mechanism was drought avoidance, achieved by dropping leaves and maintaining root growth.

Beneficial Root-Associated Microbiome during Drought and Flooding Stress in Plants.

Crop productivity is seriously threatened by the rise in the frequency and severity of drought and flood events around the world. Reduced drought and flooding stress in vulnerable species and ecosystems depends on our ability to comprehend how drought and flooding affect plant physiology and plant-associated microbes. Involvement of both abscisic acid ABA-dependent and ABA-independent pathways has been noted during drought. Hypoxic conditions impede hydraulic conductance, nutrient uptake and plant growth and development, as well as root aerobic respiration. The root microbiome, which works with the roots during drought and flood, is made up of plant growth-promoting rhizosphere, endophytes and mycorrhizas. A large number of phytohormones, primarily auxins, cytokinin and ethylene, as well as enzymes like 1-Aminocyclopropane-1-Carboxylate deaminase (ACC deaminase) and metabolites like exopolysaccharides are produced by rhizospheric microbes. These phytohormones, enzymes and metabolites have role in the induction of systemic drought tolerance in plants. Under hypoxia, anaerobic microbes with the potential to harm the plant due to their pathogenic behavior or soil denitrification ability are more likely to be present in the rhizosphere and roots. This review concentrates on the primary mechanisms of plant-microbe interactions under drought and flood stress as well as the importance of flood and drought-tolerant microbes in maintaining and increasing crop plant productivity under stress.