Identificação e seleção em campo de progênies de cafeeiro resistentes ao Meloidogyne exigua

Abstract

This work aimed at evaluating, under field conditions, the performance of coffee progenies in order to select them to obtain resistant cultivars to M. exigua and with superior agronomic traits compared to traditional cultivars. The experiment was conducted in naturally infested area by M. exigua, in Ouro Verde Farm, located in Campos Altos city /MG. The plant material consisted of 23 progenies with potential for resistance to root-knot nematode, and seven cultivars used as checks (Catuaí Vermelho IAC 99, Catuaí Amarelo IAC 62, Topázio MG 1190, Rubi MG 1192, Acaiá Cerrado MG 1474, Icatu Precoce IAC 3282 and Icatu Amarelo IAC 2942). The progenies refer to the fourth generation from cross between Timor Hybrid and Catuaí and they were obtained from the coffee breeding program conducted by EPAMIG/UFV/UFLA in Minas Gerais State. The experimental design was randomized blocks with four replications, totaling 120 plots and each plot consisted of eight plants. The spacing used was 4.0 x 0.8 m between rows and plants, respectively, corresponding to a total area of 3072 m2. Evaluated characteristics were productivity in bags of conditioned coffee per ha, percentage of fruit at cherry stage, percentage of floating fruits, high sieve classification, bean/fruit weight ratio, vegetative vigor, number of eggs of M. exigua/gram of root (NEGR) and number of galls (NG). The Pearson correlation analysis was done from the productivity, NEGR and NG. Genetic parameters estimatives and prediction of gains of selection were also performed. The results show that progenies 514-7 4-C130, 493-1-2-C134 and 518-2-10-C408 have the highest values of productivity on the average of four evaluated biennia, remaining in the group of the most productive over the years. The parasitism of M. exigua in coffee roots interferes negatively on productivity and there is a positive correlation with high magnitude between NG and NEGR. As regards the reaction to M. exigua, the progenies 436-1-4-C26, 514-7-14-C73, 514-7-4-C130, 493-1-2-C134, 514-7-16-C208, 493-1-2-C218 and 514-5-2-C494 are shown resistant. In general, the progenies show great genetic variability for all traits. The index based on the sum of "ranks" provides simultaneous gains higher than for direct and indirect selection. The progenies 493-1 2-C134, 514-7-4-C130, 518-2-10-C408 and 514-5-2-C494 are indicated for the advancement of generations based on two analytical procedures for prediction of gains, especially the progeny 493-1-2-C134 which shows superiority in all evaluated traits.