Genetic mapping, synteny, and physical location of two loci for Fusarium oxysporum f. sp. tracheiphilum race 4 resistance in cowpea [Vigna unguiculata (L.) Walp]

Abstract

Fusarium wilt is a vascular disease caused by the fungus Fusariumoxysporum f.sp. tracheiphilum (Fot) in cowpea [Vignaunguiculata (L.) Walp]. In this study, we mapped loci conferring resistance to Fot race 4 in three cowpea RIL populations: IT93K-503-1 × CB46, CB27 × 24-125B-1, and CB27 × IT82E-18/Big Buff. Two independent loci which confer resistance to Fot race 4 were identified, Fot4-1 and Fot4-2. Fot4-1 was identified in the IT93K-503-1 (resistant) × CB46 (susceptible) population and was positioned on the cowpea consensus genetic map, spanning 21.57–29.40 cM on linkage group 5. The Fot4-2 locus was validated by identifying it in both the CB27 (resistant) × 24-125B-1 (susceptible) and CB27 (resistant) × IT82E-18/Big Buff (susceptible) populations. Fot4-2 was positioned on the cowpea consensus genetic map on linkage group 3; the minimum distance spanned 71.52–71.75 cM whereas the maximum distance spanned 64.44–80.23 cM. These genomic locations of Fot4-1 and Fot4-2 on the cowpea consensus genetic map, relative to Fot3-1 which was previously identified as the locus conferring resistance to Fot race 3, established that all three loci were independent. The Fot4-1 and Fot4-2 syntenic loci were examined in Glycine max, where several disease-resistance candidate genes were identified for both loci. In addition, Fot4-1 and Fot4-2 were coarsely positioned on the cowpea physical map. Fot4-1 and Fot4-2 will contribute to molecular marker development for future use in marker-assisted selection, thereby expediting introgression of Fot race 4 resistance into future cowpea cultivars.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-013-9991-0) contains supplementary material, which is available to authorized users.

Grain Legumes

“…In the California Blackeye cowpea-breeding program, transferring aphid, nematode, and Fusarium wilt resistances into improved versions of the current varieties CB27, CB46, and CB50 is being achieved with a MABC approach. For example, the QTLs identified by Pottorff et al (2012Pottorff et al ( , 2014 for resistance to Fusarium wilt races 3 and 4 are being transferred through MABC into new lines. CB46 is race 3 resistant but lacks race 4 and aphid resistances, so markers for the resistance loci can be used to select the donated favorable alleles for resistances to aphid and Fusarium race 4 and also confirm the presence in the background of the favorable haplotypes for Fusarium race 3 and root-knot nematode resistances.…”

“…The 1536-SNP platform and the genetic maps were used to identify the genomic positions of the many QTLs for important cowpea traits described earlier. The QTL discovery has been based on extensive phenotyping for agronomic as well as abiotic and biotic stress resistance traits in the genotyped biparental RIL 7 Cowpea populations and cowpea diversity panels (Huynh et al 2013b;Muchero et al 2013;Lucas et al 2013b;Pottorff et al 2014). The SNP calls associated with the favorable alleles at each QTL provide the marker haplotypes needed for positive trait selection for use in foreground selection.…”

Genetic analysis of Fusarium wilt resistance in cowpea (Vigna unguiculata Walp.)

“…We propose that the genes symbol conferring resistance to Fot race 1 in “cowpea” should be designated as Fot1‐1 in accordance with the previous designation established for races 3 and 4 by Pottorff et al. ().…”

“…The scores used to compute the genetic distance are contained in the supplementary information Table S1. In previous studies, only SNP markers have been reported in discriminating Fusarium wilt resistant and susceptible lines in cowpea (Pottorff et al., ). Identification of an SSR‐linked marker to Fot in this study is a landmark that will help the low budget laboratory breeders to do the marker‐assisted selection (MAS) using SSR markers to shorten the breeding cycle in developing cowpea cultivars for Fusarium wilt resistance.…”

“…The disease causes substantial yield losses ranging from 30% to 100% (Reddy et al., ). In the United States, high plant mortality with severe overall yield loss has also been reported (Pottorff, Li, Ehlers, Close, & Roberts, ).…”