Breeding for resistance to Meloidogyne exigua in Coffea arabica by introgression of resistance genes of Coffea canephora

Breeding for resistance to root-knot nematode Meloidogyne exigua in coffee may help in controlling this nematode, which causes substantial harvest los ses throughout Latin America. Accessions of Coffea arabica, C. canephora an d lines derived from the Timor Hybrid (wild C. arabica X C. canephora inter specific hybrid) were tested in a greenhouse for resistance to gall formati on by counting individual galls on the roots of plants inoculated with seco nd-stage juveniles of a M. exigua population from Costa Rica. The level of introgression from C. canephora was also assessed on 28 resistant and susce ptible genotypes in a molecular study with amplified fragment length polymo rphism (AFLP) markers. The frequency of resistant plants was very low or ev en nonexistent in C. arabica and very high in C. canephora with > 78% immun e plants and 100% resistant plants. Several lines derived from the interspe cific hybrid revealed a high level of resistance similar to that observed i n the parent C. canephora species. A molecular study of Timor Hybrid-derive d lines revealed high variability for the number of markers present in the study genotypes. A larger number of introgression markers was found in the group of resistant genotypes than in the susceptible genotypes. However, th ere were also lines with little introgression that had retained resistance. Based on genetic distances calculated from these markers, two groups of li nes were revealed: those derived from Timor Hybrid CIFC1343, and those deri ved from Timor Hybrids CIFC832/1 and CIFC832/2, which may indicate the exis tence of different resistance genes in the two groups. The segregations obs erved in F-1 and F-2 progeny may be explained by at least a dominant gene. The lines derived from the Timor Hybrid are a worthwhile source of resistan ce to M. exigua that can be exploited to improve C. arabica with the help o f molecular-assisted selection.