Genetic Gain in the Resistance of Arabica Coffee Progenies to Root‐Knot Nematode

Abstract

The nematode Meloidogyne exigua infests Arabica coffee (Coffea arabica L.) plants, leading to severe growth reduction in young trees and decreased bean yield. We investigated the responses of coffee plants to this nematode and estimated the genetic gain in progenies derived from the cross between the cultivar Catuaí and the Timor hybrid. We evaluated 85 F4:5 progenies; the cultivars Mundo Novo IAC 379‐19 and Catuaí Vermelho IAC 99 were used as susceptible controls, and Paraíso MG H 419‐1 and IPR 100 were used as resistant controls. Progeny responses were evaluated using the gall index (GI), reproduction factor (RF), reproduction factor reduction (RFR), and number of eggs and juveniles (J2) per gram of roots (NEJGR). The cultivars IPR 100 and Paraíso MG H 419‐1 and 75 progenies were resistant to M. exigua. Little or no segregation for resistance was observed within the progenies, indicating potential homozygosity at this locus. The GI, RF, RFR, and NEJGR showed high genotypic correlation. The correlated response of decreased NEJGR when selected indirectly by GI was higher than that by direct selection. The GI scale allowed genetic gain to decrease the nematode population and increase resistance; therefore, it can be used as a selection criterion. Linear regression showed that the NEJGR mean was reduced by a value of 450 per selection cycle, which led to a change in the phenotypic mean and explained 95% of the variation. Thus, successive selection cycles could prevent nematode development in coffee tree roots.