Acúmulo de fitomassa e teor de clorofila em plântulas de cultivares de arroz sob estresse por frio

The cold stress during the early stages of rice development can cause uneven and decrease in germination rate. The aim of this study was to evaluate different rice cultivars related to the chlorophyll content and biomass accumulation, the latter measured after a period of recovery, in response to this stress, looking further establish which variable best serves the discrimination of genotypes for the trait in question. To this end, the follow cultivars were used: Ambar, Diamante and Oro, considered tolerant; BRS Fronteira and BRS Pampa, moderately tolerant; IRGA 417, BRS Pelota, BRS Taim and BRS Sinuelo CL, seen as sensitive to cold. The sowing was carried out in vessels of 0.2 L with vermiculite substrate in a completely randomized design with three replications. After seven days at 25 °C plants were exposed to 4 °C for 24 h and, after that, was estimated chlorophyll content of plants. Subsequently, these seedlings were left for 72 h at 25 °C for recovery and then, samples for the measurement of dry fitomassas were taken. There were significant differences between genotypes and groups of genotypes for the seedling dry weight and chlorophyll content when under stress by cold. The chlorophyll content are not efficient to distinguish rice cultivars, on the other hand, the dry mass of roots and total of seedlings, evaluated after a period of stress recovery by cold, is effective in separating rice genotypes under this stress and may be used as a tool for this purpose.