Alterações fisiológicas de sementes de feijão caupi tratadas com os ácidos salicílico ou ascórbico e submetidas ao estresse salino

Abstract

Salinity stands out as one of the main environmental stresses, affecting the productivity of many crops, including cowpea beans, which despite being well adapted to low rainfall conditions and high temperatures, is a species sensitive to salinity. The objective of the present study was to verify a possible residual protective effect of salicylic or ascorbic acids in cowpea, cv. BRS Potengi, even after drying the seeds, with subsequent sowing in saline conditions. Three experiments were carried out, the first of which was conducted with the purpose of finding the imbibition period required for the seeds to reach Phase II of the three phase imbibition process, without initiating Phase III. In addition to comparing whether the use of the same seeds for all imbibition periods (methodology I) or the use of new seeds at each period (methodology II) could interfere with the construction of the imbibition curve (30 '; 1; 3; 6; 9; 12; 18 and 24 hours). In the case of methodology II the seeds after each imbibition period were divided into two fractions, one of them being kept moist (moist fraction) until sowing and the other being submitted to the drying process (dry fraction). It was evaluated: water content - TA; Germination (primary root protrusion - PRP); Rate of protrusion of the primary root - IVPR; Protrusion speed coefficient of the primary root - CVPR; Mean protrusion time of the primary root - TMPR and electrical conductivity - CE. The second experiment consisted of two independent assays in which the seeds were physiologically conditioned with salicylic acid solutions (0.0, 0.25, 0.5 and 1.0 mM) and ascorbic acid (0.0 , 0.5, 1.0, 1.5, 2.0 and 2.5 mM) for 12 hours, after which the seeds of each of the acid concentrations were also divided into two fractions, ie wet and dry. Subsequently, it was determined: TA; PRP; IVPR; CVPR; TMPR; Percentage of germination (percentage of normal seedlings) - G; First germination count - PCG; Length of aerial part - CPA and root system - CSR; Dry mass of the aerial part - MSPA and of the root system - MSR and CE. The concentrations of each acid that provided the best physiological responses were used for the third experiment. The third experiment involved pre-imbibition treatments, that is, seeds without physiological conditioning (No CF - control); Seeds with physiological conditioning in distilled water (CF water - hydrocondicionamento); Seeds with physiological conditioning in salicylic acid solution (CF AS: 0.5 mM) and seeds with physiological conditioning in ascorbic acid solution (CF AA: 1.5 mM) for 12 hours. Afterwards, the seeds of each of the physiological conditioning treatments were divided into the moist fractions (without drying) and dried (with drying), and then seeded on a substrate germitest paper moistened with sodium chloride solutions of different osmotic potentials (0, 0, -0.3, -0.6, -0.9 and -1.2 MPa) at 25 ºC. It was evaluated: TA, EC, percentage of membrane damage; G; PCG; CPA; CSR, MSPA and MSR. For all the experiments the completely randomized design was used. In the first experiment the seeds of cowpea beans, cv. BRS Potengi, presented a three-phase germination pattern, showing that there was no difference in the seed behavior for the two methodologies used and after 12 hours of imbibition the seeds were found in phase II of the three-phase imbibition process. In the case of methodology II there was no significant difference for the germination and vigor parameters between the different imbibition periods. The second experiment showed that the use of the salicylic acid concentrations gave better results in the germination of the seeds compared to the controls (unconditioned and hydrocondicionadas), emphasizing the concentration of 0.5 mM; however, the concentration of 1.5 mM, on the characteristics related to the germination process and the initial development of the seedlings of the seeds treated with ascorbic acid. The use of the drying process after the physiological conditioning of the seeds in said acids, in general, impaired the vigor and development of the seedlings. Physiological conditioning with ascorbic (1.5 mM) or salicylic acid (0.5 mM) for 12 hours was not able to alleviate the deleterious effects of salt stress on germination and initial development of cowpea, Cv. BRS Potengi, regardless of the use of drying after the pre-hydration treatments. Saline stress with osmotic potential from -0.3 MPa sodium chloride caused a decline in the germination of cowpea, cv. BRS Potengi, germination process delay and seedling length reduction and dry mass accumulation.