Characterization of the Fusarium wilt resistance Fom-2 gene in melon

Abstract

The melon gene Fom-2, which confers resistance to Fusarium oxysporum f.sp. melonis (Fom) races 0 and 1, has been previously characterized by map-based cloning, and it encodes a protein with a nucleotide binding site (NBS) and leucine-rich repeats (LRRs). Here, we used the primer Fom2-LRR1639 to clone and sequence a partial LRR region of the Fom-2 gene in 11 melon accessions resistant to Fusarium wilt from various geographic regions. Our work revealed that the structure of the partial LRR domain is highly conserved between eight of these resistant accessions and is similar to the resistant allele in the previously characterized PI-161375 line. Conversely, PI-124111 is a unique line that presents the same resistant allele that was previously described in the MR-1 line. The accession Cum-355 presents a protein that differs from that encoded by both the resistant lines PI-161375 and MR-1. This result suggests that Cum-355 has a new resistant allele of Fom-2 that determines the same specificity. Importantly, based on the sequence of the Fom-2 LRR domain, two sequence characterized amplified region (SCAR) markers, Fom2-R408 and Fom2-S342, were developed for Fom-2 resistant and susceptible alleles, respectively. These allele-specific PCR markers could be used as co-dominant markers when their primer pairs were combined in a multiplex PCR reaction. The specificity of these functional markers (FM) was validated on a set of 27 genotypes representing several melon types. These FM markers are expected to enhance the reliability and cost-effectiveness of marker-assisted selection for the Fom-2 gene in melon.