Depressão endogâmica em híbridos de sorgo granífero sob estresse hídrico

Abstract

The sorghum is classified as the fifth most important cereal in the world is tolerant to water deficit, being an excellent alternative of cultivation in drought and low fertility sites. Water deficiency consists of the amount of available water, where it is less than the amount needed to meet the water needs of the crop. The objective of this work was to evaluate agronomic characteristics under water stress, to determine inbreeding depression in endogamous populations of commercial hybrids of sorghum. Five commercial hybrids of sorghum, recommended for cultivation in the Center-West region of Brazil, and their respective generations of self-fertilization (F2 and F3) were used. The experimental design was a randomized complete block design, in a factorial scheme (5 x 3), the plants were submitted to three water conditions and irrigated four days with volumes 100 (1100 ml), 75 (825 ml) and 50% (550 ml) of soil water retention capacity, representing 0, 25 and 50% of stress, respectively, water availability was determined by calculating the field capacity. The evaluated variables were plant height, stem diameter, flowering, aerial shoot dry mass, root dry mass and grain mass. The water stress provided a decrease in the averages of the evaluated variables: diameter, flowering, aerial shoot dry mass, root dry mass and grain mass. Water stress significantly interfered with the average of all evaluated agronomic characteristics, which showed a significant difference. Sorghum hybrids were more tolerant when the soil presented 25% (1/4) of its volume with water and is not recommended for cultivation in places with marked stress or excess water. Commercial hybrids 50A50, 50A70 and Fox have been highlighted because they are more tolerant when submitted to stress, however, for the grain mass, Buster and Fox, the most suitable for environments with low rainfall or with water restriction. The high productivity of grains in the environment with water stress is possibly associated to the rapid development of the plants, while in the irrigated environment it is associated to the longer vegetative period. There was a great variation in depression by inbreeding and heterosis for the characters evaluated, indicating different behaviors between the generations. There was expression of inbreeding depression and heterosis for all the variables under study. The 50A50 population presented a low rate of inbreeding depression for plant height, stem diameter and flowering, and the populations 50A70 and DKB 550 stood out for the grain mass, with a lower index of depression, being indicated in obtaining promising strains and recurrent intrapopulation selection. The Fox population presented a high index of inbreeding depression for the stem diameter, root dry mass and grain mass, being recommended for programs of population improvement and reciprocal recurrent selection.