Simira gardneriana M.R. Barbosa & Peixoto (Rubiaceae) is a species exclusive to the Caatinga biome. It is used as forage, firewood, and in the construction of fence posts. Species from this biome are constantly subjected to abiotic stresses, including salt and thermal stress. Thus, we evaluated the effect of irrigation water salinity on the germination and initial development of S. gardneriana seedlings at different temperatures. The experiment used seeds with an initial moisture content of about 12.32%, arranged in a factorial scheme with eight levels of salinity, obtained by the addition of sodium chloride (NaCl), diluted in distilled water at concentrations of 0.0 (control), 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, and 7.5 dS m-1, and the four temperatures 25, 30, 35, and 20-30°C, in four replicates of 25 seeds each. Salinity and temperature effects were evaluated based on germination, germination speed index, seedling shoot length, root length, shoot dry matter, root dry matter, and total dry matter. Increasing water salinity levels interfered with all variables analyzed in the germination of S. gardneriana seeds, especially at a temperature of 35°C. At temperatures of 25 and 30°C, seed germination and initial development were less affected by salinity. Simira gardneriana seeds are sensitive to salinity caused by the increase in NaCl from 1.5 dS m-1, which indicates a low tolerance of this species to saline environments. Our results show that the negative effect on the germination and initial development of S. gardneriana seedlings can be explained by the increase in salt levels and temperature, reducing their capacity to absorb water and nutrients, which indicates sensitivity responses of this species to salinity and thermal stress.

A B S T R A C TThe process of water imbibition by the seed depends on temperature and water availability, which according to the absorbed water retention capacity will determine the success of the germination process. Thus, this study aimed to investigate the effects of water stress on the germination and vigor of 'jurema-de-embira' seeds under different temperatures. The experimental design was completely randomized in a 7 x 4 factorial scheme (osmotic potential and temperature) with four replicates of 25 seeds each. The osmotic potentials of 0, -0.1, -0.2, -0.3, -0.4, -0.5 and -0.6 MPa at temperatures of 25, 30 and 35 °C and alternated of 20-30 °C, under photoperiod of 8 h, were evaluated. Germination percentage, germination speed index, shoot and root length, shoot dry biomass, root dry biomass and total biomass were evaluated. Water stress negatively affected the germination and vigor of 'jurema-deembira' seedlings from the potential of -0.2 MPa on, whose effects are more evident at the temperature of 35 ° C. The alternated temperature of 20-30 °C allowed greater tolerance to water stress for the germination of 'jurema-de-embira' seeds.Germinação de sementes de jurema-de-embira sob estresse hídrico e em diferentes temperaturas R E S U M O O processo de embebição de água pelas sementes é dependente da temperatura e da sua disponibilidade que, de acordo com a capacidade de retenção da água absorvida, determinará o sucesso do processo de germinação. Desta forma, objetivou-se verificar os efeitos do estresse hídrico na germinação e no vigor de sementes de jurema-de-embira, em diferentes temperaturas. O delineamento experimental foi inteiramente casualizado, em esquema fatorial 7 x 4 (potencias osmóticos e temperaturas) com quatro repetições de 25 sementes cada uma. Foram avaliados os potenciais osmóticos de 0; -0,1; -0,2; -0,3; -0,4; -0,5 e -0,6 MPa nas temperaturas de 25, 30 e 35 °C e alternadas de 20-30 °C, sob fotoperíodo de 8 h. Avaliaram-se a porcentagem e o índice de velocidade de germinação, comprimento da parte aérea e da raiz, massa seca da parte aérea, da raiz e total. O estresse hídrico afetou negativamente a germinação e o vigor das plântulas de jurema-de-embira a partir do potencial de -0,2 Mpa, cujos efeitos são mais evidentes na temperatura de 35 ºC. A temperatura alternada de 20-30 ºC permitiu maior tolerância ao estresse hídrico para a germinação de sementes de jurema-de-embira.