Germinação de sementes, crescimento inicial, trocas gasosas e clorofila de plantas de algodão submetidas ao estresse hídrico e salino.

Abstract

In the face of the extreme water scarcity established in the Northeast, mainly in the semi-arid region, several studies are carried out to find plants that are resistant to drought and can also be grown in areas where the water used is of salt quality. Therefore, the objective of this study is to verify the possible damages caused by germination, seedling establishment and initial growth of cotton cultivars BRS 286, BRS Topázio and BRS Verde, in addition to verifying possible changes in the variables of gas exchange. The experimental design was completely randomized, with a factorial scheme 3 x 5, with three cotton varieties being submitted to five treatments of saline or water stress. The experiments were divided into two parts and conducted at the Federal University of Campina Grande, Campus I, being the germination carried out in the laboratory, and the initial growth in a greenhouse. The germination experiment was divided in germination under saline stress (0,02; 2,5; 5,0; 7,5; 10,0 dS m-1) and germination under water stress (0,0, -0,3; -0,6; -0,9; -1,2 MPa). The initial growth was divided in the same way as the germination, but with different treatments, the saline stress being composed by the treatments of 1,1; 3,1; 5,1; 7,1; 9,1 dS m-1 and that of water stress equal to 100%; 88,75%; 77,5%; 66,25%; 55% of field capacity. The saline waters did not affect the germination of cotton seedlings, however, seedling growth and consequently total fresh and dry mass of seedlings were reduced with increasing salt levels in the substrate, with CEa of 10 dS m-1 the most damaging to these variables. In relation to initial growth, increasing levels of salts in irrigation water significantly reduced all growth, fresh mass, dry mass and relative chlorophyll index, both at 15 days after application of the treatments (DAT) and at 30 DAT, showing a decrease in their values as salt levels increased, with the CEa level of 9,1 dS m-1 being the most damaging, in addition, water salinity levels also presented significant gas exchange variables, except for stomatal conductance (gs) measured at 15 DAT. As for water stress, the germination was effectively affected, mainly from the water potential of -0,9 MPa, obtaining zero germination at -1,2 MPa potential. Consequently, the establishment of cotton seedlings was also significantly affected in water stress. In the evaluation of initial growth and gas exchange, the effect of water stress was also not different from that found for germination, because all variables analyzed were significantly affected when submitted to different levels of water deficit, with a water level of 55% of the field capacity which most adversely affected the growth and physiological process of cotton plants. In both germination and initial growth, the BRS 286 cotton cultivar presented the highest resistance to CEa levels and water deficit, followed by BRS Topázio and BRS Verde, respectively.