B. Bertrand et al., Breeding for resistance to Meloidogyne exigua in Coffea arabica by introgression of resistance genes of Coffea canephora, PLANT PATH, 50(5), 2001, pp. 637-643
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.