Indução de tolerância aos estresses térmico e hídrico em Moringa oleifera em região semiárida.

Abstract

The population increase associated with the exploitation of natural resources and climate change influences the demand for food, especially in semi-arid regions, which highlights the need for technologies for better adaptation of cultivated species. In this perspective, the objective was to induce tolerance to stresses caused by water deficit and high temperature in Moringa oleifera using the technique of conditioning seeds with blue light and ethylene. The experiment was conducted in two stages the first being at the Federal University of Campina Grande and the second at the State University of Paraíba. Stage I was the application of seed conditioning, and stage II was the formation of Moringa oleifera seedlings in a Fitotron-type growth chamber under water and heat stress, in an experiment conducted in a completely randomized design, in a 2 x 2 x 3, factorial scheme with two replacement levels of soil water lost by crop evapotranspiration – ETc (50% and 100%), two thermal conditions, one with stress (40 °C day/35 °C night) and the other without stress ( 30 °C day/25 °C night) and three seed conditionings consisting of a control - PRI 0 (unconditioned seeds), conditioning in distilled water under irradiation with blue monochromatic light - PRI 1 and conditioning in ethylene solution (500 mg L-1 of Ethrel) under irradiation with blue monochromatic light – PRI 2, with five repetitions. Cell membrane integrity, water status, osmotic adjustment indicators, antioxidative mechanism, gas exchange, photochemical efficiency, seedling dry matter accumulation were evaluated. Biometric indicators, chloroplast pigment contents, phytomass partition, growth and seedling quality indices, leaf area indices, shoot biomass production and SPAD and growth rates. Data were submitted to exploratory analysis of principal components, multivariate variance and test of means. Thermal stress, ie, a temperature variation of 40 °C day/35 °C night, caused an increase in the activity of catalase enzymes in the leaves and accumulation of total soluble proteins in the roots. Abiotic, thermal and water stresses impaired gas exchange, osmotic adjustment, photochemical efficiency and dry matter accumulation of Moringa oleifera seedlings cultivated in a phytotron growth chamber. The seedlings generated from seeds conditioned in ethylene solution under irradiation with blue monochromatic light improve the physiological and biochemical characteristics for greater tolerance to abiotic stresses. The occurrence of abiotic, thermal and water stresses simultaneously caused a reduction in the quality of Moringa oleifera seedlings in a phytotron growth chamber. However, conditioning seeds in solution with ethylene phytohormone under irradiation with blue monochromatic light improved the quality of seedlings subjected to these abiotic stresses. The combination of heat and water stress increased the water content in the roots and the succulence of the leaves. The conditioning of seeds in solution with the phytohormone ethylene under irradiation with monochromatic blue light improves the accumulation of fresh matter, the water relations

and the growth indices of Moringa oleifera seedlings under abiotic, thermal and water stress in a phytotron growth chamber.