Resistência de genótipos de algodoeiro de fibra branca à mancha angular em fase inicial de desenvolvimento

Abstract

The cotton plant (Gossypium hirsutum L.) is the plant of major importance of the Malvaceae family, and has the fiber as the main product. The cotton plant crop, as many other cropssuffer significant production losses due to the attack of pests and diseases. One of the biggest challenges found by the cotton farmer is the high cost of maintenance of the crop, due mainly to the intense phytosanitary control required by the crop. Among the diseases who causes more losses to the cotton crop, is noted the bacterial blight, caused by the bacteria Xanthomonas citri pv. Malvacearum. The disease is not effective controlled in a curative way, using chemical products, being your control dependent on the use of resistant materials. The purpose of the present study was evaluate 35 genotypes of cotton about the resistance as to the causal agent of the bacterial blight, Xanthomonas citri pv malvacearum. The experiment was fulfilled at grenhouse and at the Vegetal Bacteriology of the Universidade Federal de Uberlândia from the Universidade Federal de Uberlândia in Uberlândia – MG, from 2016 may to june. The experimental design was the randomized blocks, with a total of 35 treatments, with three repetitions each. The genotypes were inoculated at 15 days after the emergence with an agressive insulated of Xanthomonas citri pv malvacearum (race 18) from the collection of the EMBRAPA cotton. The evaluations were at 3, 5, 7, 9, 11, 13, days after the inoculation, and the severity of the infection evaluated by a visual scale ranging from 1 to 5. The results obtained through the evaluation of the severity were used for the calculation of the Area Under The Disease Progression Curve (AUDPC) and for analyzes of the genotypes for the index of disease resistance. Considering the estimate of the AUDPC there was the conformation of eight genotypes groups statistically different for the evaluation of the severity of bacterial blight, and the results obtained by the resistance index indicate that from 35 genotypes studied, only two were concepted as bacterial blight resistant genotypes, and 20 were concepted as moderately resistant. The genotypes with better performance for the resistance of the bacterial blight were FM 975 WS, SURE GROW and BRS CEDRO, ant the genotypes who more susceptibility to the disease were UFUJP15 – I, UFUJP15 – G, followed by UFUJP15 – N e Stonville 474.