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Seven races of Fusarium oxysporumf. sp. phaseoliKendrick and Snyder (Fop) cause Fusarium wilt (FW) disease of common bean (Phaseolus vulgarisL.). FW occurs worldwide and has recently become a serious disease in the central and western USA. The objectives of this research were to identify new sources of resistance to Fop, characterize the Central/South American (CA/SA) PhaseolusCore Collection for reaction to races 1, 4, and 5 Fop and determine if a previously reported sequence characterized amplified region (SCAR) molecular marker would be useful to identify resistance among accessions that make up the CA/SA Core Collection. Seedlings from the CA/SA Core Collection were screened for reaction by a root dip inoculation procedure. Among accessions evaluated for reaction to race 1 Fop, 21 were resistant, 47 intermediate, and 126 susceptible. Fifteen accessions were resistant to race 4, 61 intermediate, and 114 were susceptible. Nine accessions were resistant to both races 1 and 4, and five of the nine (PI 207373, PI 307802, PI 308908, PI 309877, PI 310842) were also resistant to race 5 Fop. All accessions resistant to races 1, 4, and 5 of Fop were characterized as Middle American, which suggests that resistance to multiple races of Fop should be more prevalent in germplasm from Middle America. The SCAR marker previously developed to identify a quantitative trait locus (QTL) associated with resistance to Fop was not associated with resistance in the Core Collection.

Fusarium oxysporumSchlectend. Fr. f. sp. phaseoliJ.B. Kendrick and W.C. Snyder (FOP) is a vascular pathogen that causes Fusarium wilt in common bean (Phaseolus vulgarisL.). This disease is an increasing problem in the western U.S., and exploitation of genetic resistance is considered the most feasible control method. The objective of this study was to detect quantitative trait loci (QTL) for Fusarium wilt resistance in a population derived from an interracial cross between FOP‐susceptible Belneb RR‐1 (race Durango) × FOP‐resistant A55 (race Mesoamerica). Seventy‐six F6‐derived recombinant inbred lines (RILs) were screened for disease severity in greenhouse inoculations and rated on a scale of 1 (resistant) to 9 (susceptible). The phenotypic data were compared to existing random amplified polymorphic DNA (RAPD) marker data using single‐factor analysis of variance. Marker U20.750 on linkage group (LG) 10 accounted for 63.5% of the phenotypic variance for this trait. Lines exhibiting the A55 banding pattern at this locus had disease severity scores that averaged 3.6 points lower than lines with the Belneb RR‐1 pattern. Two additional markers, AD4.450 on LG 3 and K10.700 on LG 11, were significant (P< 0.01) in single‐factor analysis of variance, but only marker U20.750 on LG 10 remained significant when composite interval mapping (CIM) was conducted. The tight linkage between the putative QTL and U20.750, as indicated by CIM, makes this marker a promising candidate for conversion to a sequence‐characterized amplified region (SCAR) for use in marker‐assisted selection in Fusarium wilt resistant common bean cultivar development.