Tolerância de genótipos de gergelim ao estresse salino.

Abstract

Sesame (Sesamum indicum L.) is an oilseed of relevant nutritional value and social and economic potential in Brazil but it is sensitive to salinity. This fact can limit their exploitation in areas with salinity problems, or to be irrigated with saline water. For this reason, it is necessary to identify tolerant genotypes and to adopt management practices that allow its cultivation in areas affected by salts or under irrigation with saline water upper to the threshold salinity of crop. In this context, it was aimed to evaluate the tolerance of sesame genotypes to salt stress under irrigation with saline water. The study consisted of three experiments to study the tolerance of genotypes in different management conditions by irrigation with saline water. The first experiment consisted of a study with five salinity levels of irrigation water (0.6, 1.6, 2.6, 3.6 and 4.6 dS m-1 at 25 °C) and six sesame genotypes (BRS Seda, CNPA-G2, –CNPA-G3, CNPA-G4, Branquinha and Pretinha), assigned by Embrapa Algodão. Salinity was studied on emergence and early growth of seedlings/plants until 26 days after sowing (DAS), evaluating emergence, early growth and biomass. In the second experiment, the same salinity levels were studied since vegetative growth (29 DAS) up to grain production. It were evaluated growth, physiological parameters, biomass and grain yield. Finally, the third experiment consisted of a study of salt stress on the same genotypes, differentiating the managements of salinity (plants without salt stress throughout the

experiment, irrigated with water supply - CEa = 0.6 dS m–1 at 25 ºC; plants under salt stress in the vegetative phase, irrigating the plants with water of CE = 3.6 dS m-1 at 25 °C, since the vegetative phase (11 DAS) up to the flowering, and plants under salt stress during production phase, irrigating the plants with water CEa = 3.6 dS m-1 at 25 ºC from flowering until the end of the cycle, in order to evaluate, in this case, growth and biomass production). Water salinity did not affect the percentage of emergency but it impaired the rate of seedling emergence, early growth and biomass production. The‘CNPA-G2’ and ‘Branquinha’ were affected by salinity phase, while ‘BRS Seda’, ‘CNPA-G3’, ‘CNPA-G4’ and ‘Pretinha’ were moderately tolerant to salinity up to 2.6 dS m-1 in the initial phase. Physiological parameters of chlorophyll fluorescence, gas exchange, growth, yield and seed oil content were compromised by increasing salinity of irrigation water. Based on the relative reduction of the production of seeds, ‘Pretinha’, ‘Branquinha’ and ‘CNPA-G4’ were tolerant to salinity of 1.6 dS m-1 and moderately tolerant of salinity in irrigation water of 2.6 dS m-1 while ‘BRS Seda’ and ‘CNPA-G2’ were moderately tolerant to salinity of 1.6 dS m-1. Irrigation with saline water (3.6 dS m- 1) in the vegetative phase is detrimental to growth, development and final production of sesame, with the largest reduction in seeds oil content occurs when plants are subjected to salt stress during the production phase.