GENÉTICA POPULACIONAL DE Gossypium hirsutum RAÇA MARIE GALANTE NO BRASIL SEGUNDO CONDIÇÕES DE ESTRESSE HÍDRICO E FERTILIDADE DO SOLO

Abstract

The mocó cotton (Gossypium hirsutum r. marie galante) represents an important variability source for genetic breeding of commercial cotton. The Embrapa has been collecting and conservating accessions of this type of cotton, because they present a wide morphological and technological fiber variation, which is still little explored. Another interest in this cotton is its good performance in the northeastern semi-arid region, which makes us believe that this species has been selected by adverse soil and climate conditions developing superior genotypes. The lack of available organized data on the accesses collected from this type of cotton results in little exploration of its genetic potential. The objective of this work was to genetically characterize accessions of mocó cotton belonging to the Embrapa Cotton germplasm, using microsatellite markers, as well as the selection of genotypes that may have greater tolerance to dry climatic conditions and low soil fertility. We use geographic and maintenance in situ data of 331 plants of mocó cotton, of which 280 were genotyped, 254 were found in nine Northeastern states and the remaining 26 in two northern states. Thematic collections (TCs) for dry periods and low fertility were defined based on the geographical coordinates of the accessions and the interactive maps of Brazil climates and agricultural potential obtained from the website of the Brazilian Institute of Geography and Statistics (IBGE). Twelve microsatellite markers were used for genotyping. Genetic analysis was performed based on the number of alleles per locus (A) and private, expected (HE) and observed (HO) heterozygosity. The genetic relationship between the thematic collections was analyzed throught the genetic distance (GD) of Rogers (modified), besides the F statistic of Wright to verify genetic structuration. About in situ maintenance, the cotton plants were most found in farms (65,3%). Considering the urban and rural areas, 68,6% of the plants were kept as backyard or dooryard plants. There were three thematic collections, being of most interest the CT3, constituted by individuals collected in great periods of dry and low soil fertility. Were detected in the total sample 71 alleles, with an average of 5.9 per loco, ranging from 3 to 9. The mean HE per loco was high 0.53, however HO, was low, 0.15, corroborating with high fixation index, f = 0.72. Although it was verified that the three gene pools, represented by CTs, presented low and significant genetic differentiation (FST = 0.05, p < 0.05), the descriptive genetic diversity between the groups was not statistically different considering the Wilcoxon test (p > 0.05). The FST value corroborated with the low average genetic distance between the thematic collections, 0.062. Despite the low genetic differentiation between regions with different periods of dry and soil fertility levels, the germplasm presents a similar and expressive genetic diversity organized in homozygous genotypes. Thus, it can be used as an allelic source in valuation studies for use in breeding programs