Tolerância ao frio e efeito da época de supressão da irrigação no desempenho de sementes de arroz (Oryza sativa L.)

Abstract

The study aimed to evaluate the cold tolerance of four rice cultivars under stress conditions (13-18°C) in stages S0-V3 and check the season effect of irrigation suppression on the quality of rice seeds from the cultivars BRS Atalanta, BRS Querência and BRS 7 Taim. The study consisted on two experiments performed independently. In the first experiment, it was evaluated the cold tolerance of seeds of the cultivars Brilhante, BRS SCS Tio Taka, BRS Querência and BRS7 Taim under stress conditions (13-18°C) during early development (S0-S3). The evaluative parameters were: speed index of total emergence, speed index of emergence of the stage V1, V2 and V3, index of cold tolerance (ICT), index of susceptibility to cold (ISC), index of cold intensity (ICI), geometric average (GA), chlorophyll content (CC) and seedling length (SL). The Brilhante cultivar showed tolerance to the temperature of 13-18°C, measured by the speed index of total emergence, speed index of vegetative stages, tolerance index, geometric average, chlorophyll content and seedling length at the initial development. In the second experiment, it was used seeds from the cultivars BRS Atalanta, BRS Querência and BRS 7 Taim and it was conducted in two stages. In the first stage, it was made the irrigation suppression in four seasons: Season 1: stage of panicle exsertion (R3) Season 2: stage of milky grain (R6) Season 3: stage of pasty grain (R7), and Season 4: physiological maturity (R9). In the second stage, it was performed the analysis of seed quality harvested for each treatment, through the germination test, cold test, accelerated aging, electrical conductivity, weight of a thousand seeds and seed health. It was not possible to assess the season of irrigation suppression, in the stages of panicle exsertion, milky grain, pasty grain and physiological maturity due to the high rainfall occurred throughout the reproductive phase of rice seeds of the three cultivars evaluated. The high rainfall combined with high temperature were the main factors that favored the incidence of fungus from the genus Aspergillus sp., Penicillium sp., Fusarium sp., and Bipolaris sp. on the seeds of the cultivars in study.