Aumento da temperatura do ar noturna e do déficit hídrico em genótipo de algodoeiro

Abstract

Global warming has led to an increase in nocturnal air temperatures and variations in rainfall that can interfere with the development of agricultural crops. However, many criticisms are made regarding the causes of this warming, if they are due to anthropogenic actions or natural variations. The aim of Chapter I was to evaluate the tendency of air temperature increase in the city and the farm, both in Uberlândia-MG. And in Chapter II, to evaluate the influence of the increase of the nocturnal air temperature and the water deficit in the physiology of the cotton during the reproductive phase of different genotypes. For the first study, data were collected on climatic variables of the INMET Uberlândia Station and the Capim Branco Meteorological Station - UFU. The temperature data analyzed were for the years 2011, 2012, 2013, 2014, and 2017, and were submitted to analysis of variance by the Tukey test at 0.05 significance and linear regression analysis. The second study was carried out in a greenhouse, in the same experimental farm, from September to December 2017. In order to increase the temperature of the night air, a thermal blanket was used between the vessels, increasing the temperature from 8 p.m. to 12 a.m., for two weeks. The placing of the water deficit began with the flowering and remained for two weeks, at the same time as the air temperature was increased. The experiment was a randomized block design with three factors: two temperatures, two irrigation levels and five cotton genotypes (UFUJP-E, UFUJP-M, UFUJP-Z, UFUJP-H, and FM-966) with four blocks. Statistical analysis was performed by means of joint evaluation. The analysis consisted of measuring the water potential of the xylem (MPa), cellular respiration rate (CO2 olm-s-¹ ²) and counting flower buds and flowers. In the first study, no significant tendency was observed for the diurnal temperature at the farm. On the contrary, there was an increase of 0.43ºC in the city. There was an increase of 0.07 ° C in each year in the daily average of the farm, different from the one observed in the city (P> 0.05). The nocturnal temperature tended to increase in the farm, 0.08 ° C each year, and in the city, it was not significant. The averages of all temperatures were higher in the city when compared to the farm. In the second study, the cotton genotypes were not influenced by the increase in the nocturnal air temperature and the water deficit in the foliar respiration rate. In relation to the water potential of the xylem, the UFUJP-E genotype was not influenced by the increase in night temperature or water deficit. The UFUJP-H genotype presented more negative water potential in the treatment with an increase in the nocturnal air temperature and no deficit, and the UFUJP-Z one showed the most negative water potential under normal temperature and water deficit. The water deficit interfered in the picking of flower buds and flowers for the UFUJP-H genotype, with different behavior for the UFUJP-Z genotype, which may demonstrate that this genotype is more tolerant when subjected to hydrous stress.