ABSTRACT
Leaf rust caused by the fungus Hemileia vastatrix is the most devastating disease of arabica coffee ( Coffea arabica). Therefore, developing leaf rust-resistant varieties has been a breeding objective of the highest priority in many countries. The purpose of the present work was to gain insight into the mechanism of introgression into C. arabica of a leaf rust resistance gene from C. liberica (i.e. S(H)3 resistance factor) and to identify associated molecular markers. An F(2) progeny (i.e. 101 individuals) derived from a cross between Matari, an arabica accession and liberica-introgressed line S.288, was evaluated for resistance against three different races of H. vastatrix. The progeny segregated for the S(H)3 gene in a 3:1 ratio, as expected for a single dominant gene. Amplified fragment length polymorphism analysis of a population subset using 80 different primer combinations revealed that at least half of the total polymorphism observed in the population is associated with introgression of C. liberica chromosome fragments. Furthermore, 15 primer combinations generating candidate marker bands associated with the S(H)3 resistance gene were used to analyse the whole F(2) population. A total of 34 marker bands originating from S.288 and attributable to introgression were scored. None exhibited segregation distortion. Linkage analysis revealed only three distinct introgressed fragments corresponding to a total length of 52.8 cM. Twenty-one markers were strongly associated (LOD score >14) with the S(H)3 gene and were grouped together in a single linkage group of 6.3 cM. The results are discussed in relation to the efficient use of genetic resources in arabica breeding.
