| Crop losses caused by viral pathogens are a major limitation to production of Capsicum. Cucumber mosaic cucumovirus (CMV) is one of the most significant pathogens of pepper worldwide. CMV resistance has been a formidable breeding objective due to complex inheritance, environmental and isolate-specific effects on expression and levels of resistance, and varying levels of resistance as a result of inoculation technique. A new CMV resistance source, C. frutescens 'BG2814-6', is presented and evaluated and a backcross breeding program is described in which this resistance is transferred into three commercial pepper types.;A second major class of viral pathogens infecting pepper are potyviruses, members of the largest family of plant viruses, the Potviridae. A dominant gene conferring resistance to pepper mottle potyvirus (PepMoV), Pvr7 , is reported and characterized. A dominant potato virus Y (PVY) resistance gene that is linked or allelic to Pvr7 is also reported. Pvr7 is tightly linked but distinct from Pvr4, the only other dominant pepper potyvirus resistance (R) gene characterized to date. These loci, along with Tsw, which confers resistance to tomato spotted wilt tospovirus, comprise the first identified R gene cluster in pepper. The Pvr4/Pvr7 cluster is similar in both inheritance and phenotype to a cluster of dominant R genes in potato conferring resistance to PVY and potato potyvirus A, but these clusters do not appear to be orthologous.;In order to examine more comprehensively the organization of R loci across related genera, positions of known R genes and R gene homologues, were compared using pepper, tomato, and potato comparative maps. R genes occurred at corresponding positions across these genomes more frequently than expected by chance; however, R genes conferring resistance to closely related pathogens rarely were found in corresponding positions in two genera. Homologues of cloned R genes mapped to syntenous positions in related solanaceous genomes and often mapped to additional positions corresponding to other solanaceous R genes/gene clusters. This suggests that, while pathogen specificity may be rapidly evolving, general R gene function may be conserved throughout divergence of genera, and has implications for the utility of comparative mapping to identify novel sources of resistance. |
