Seleção de genótipos de arroz irrigado responsivos ao aumento da concentração de dióxido de carbono atmosférico e investigação do fenômeno de tolerância

Abstract

Climate changes caused by increased emissions of carbon dioxide and the abiotic stresses associated with this effect (water stress and extreme temperatures) have challenged scientists to understand these effects on cultivated plants to better adapt systems to a resilient agriculture. In this sense, the general objectives of the thesis were: 1) to characterize and select rice genotypes in terms of responses to the increase in CO2; 2) to evaluate the priming effect of the water deficit in the vegetative stage on the responses of rice plants subjected to heat stress in anthesis. To achieve these objectives, two studies were carried out. The results of the first study showed that genotypes with a positive grain yield ratio between the low and normal density ratio are also more responsive to CO2. The rice genotypes present contrasting responses to the increase in atmospheric CO2. The Querência and EP106 genotypes showed greater responsiveness to high CO2 in terms of grain yield. The results referring to the second study indicate that in the concentration of 400ppm CO2 the previous stress due to water deficit in the vegetative stage reflects in the reduction of the H2O2 content in flag leaves when the plants are exposed to severe heat stress in the anthesis. While at 700ppm CO2 the enzyme antioxidant system presents greater activity under severe heat stress in anthesis when the plants are previously subjected to water deficit in the vegetative stage. In addition, the increase in superoxide dismutase (SOD) activity on the flag leaf, the greater expression of OsHSP70.6 in spikelets in 400ppm CO2, and the increase in the expression of OsHSP70CP1 in spikelets in 700ppm CO2 act favoring cross-tolerance at the biochemical and molecular level between water deficit and moderate heat stress. Finally, the study indicates that rice plants previously exposed to water deficit have a certain ability to improve responses in terms of antioxidant metabolism and heat shock proteins when subjected to high temperature.