GERMINATION AND VIGOUR IN SEEDS OF THE COWPEA IN RESPONSE TO SALT AND HEAT STRESS

Salinity is prejudicial to plant development, causing different types of damage to species, or even between genotypes of the same species, with the effects being aggravated when combined with other types of stress, such as heat stress. The aim of this study was to evaluate the tolerance of cowpea genotypes (Vigna unguiculata L. Walp.) to salt stress at different temperatures. Seeds of the Pujante, Epace 10 and Marataoa genotypes were placed on paper rolls (Germitest (R)) moistened with different salt concentrations of 0.0 (control), 1.5, 3.0, 4.5 and 6.0 dS m(-1), and placed in a germination chamber (BOD) at temperatures of 20, 25, 30 and 35 degrees C. The experiment was conducted in a completely randomised design, in a 3 x 4 x 5 scheme of subdivided plots, with four replications per treatment. The variables under analysis were germination percentage, first germination count, shoot and root length, and total seedling dry weight. At temperatures of 30 and 35 degrees C, increases in the salt concentration were more damaging to germination in the Epace 10 and Pujante genotypes, while for the Marataoa genotype, damage occurred at the temperature of 20 degrees C. At 25 degrees C, germination and vigour in the genotypes were higher, with the Pujante genotype proving to be more tolerant to salt stress, whereas Epace 10 and Marataoa were more tolerant to high temperatures. Germination in the cowpea genotypes was more sensitive to salt stress when subjected to heat stress caused by the low temperature of 20 degrees C or high temperature of 35 degrees C.