Genetic and Physical Mapping of Candidate Genes for Resistance to Fusarium oxysporum f.sp. tracheiphilum Race 3 in Cowpea [Vigna unguiculata (L.) Walp]

Abstract

Fusarium oxysporum f.sp. tracheiphilum (Fot) is a soil-borne fungal pathogen that causes vascular wilt disease in cowpea. Fot race 3 is one of the major pathogens affecting cowpea production in California. Identification of Fot race 3 resistance determinants will expedite delivery of improved cultivars by replacing time-consuming phenotypic screening with selection based on perfect markers, thereby generating successful cultivars in a shorter time period. Resistance to Fot race 3 was studied in the RIL population California Blackeye 27 (resistant) x 24-125B-1 (susceptible). Biparental mapping identified a Fot race 3 resistance locus, Fot3-1, which spanned 3.56 cM on linkage group one of the CB27 x 24-125B-1 genetic map. A marker-trait association narrowed the resistance locus to a 1.2 cM region and identified SNP marker 1_1107 as co-segregating with Fot3-1 resistance. Macro and microsynteny was observed for the Fot3-1 locus region in Glycine max where six disease resistance genes were observed in the two syntenic regions of soybean chromosomes 9 and 15. Fot3-1 was identified on the cowpea physical map on BAC clone CH093L18, spanning approximately 208,868 bp on BAC contig250. The Fot3-1 locus was narrowed to 0.5 cM distance on the cowpea genetic map linkage group 6, flanked by SNP markers 1_0860 and 1_1107. BAC clone CH093L18 was sequenced and four cowpea sequences with similarity to leucine-rich repeat serine/threonine protein kinases were identified and are cowpea candidate genes for the Fot3-1 locus. This study has shown how readily candidate genes can be identified for simply inherited agronomic traits when appropriate genetic stocks and integrated genomic resources are available. High co-linearity between cowpea and soybean genomes illustrated that utilizing synteny can transfer knowledge from a reference legume to legumes with less complete genomic resources. Identification of Fot race 3 resistance genes will enable transfer into high yielding cowpea varieties using marker-assisted selection (MAS).

The Synthetic Elicitor 2-(5-Bromo-2-Hydroxy-Phenyl)-Thiazolidine-4-Carboxylic Acid Links Plant Immunity to Hormesis

“…Relatively mature plants could tolerate higher concentrations of DMSO better than younger plants, so the chemical concentrations increased over time and the amount sprayed increased for thorough coverage as plant size increased: 24 h prior to inoculation = 100 mM BHTC, 2 mL per plant; week 1 post inoculation = 100 mM BHTC, 2 mL per plant; week 2 post inoculation = 200 mM BHTC, 3 mL per plant; week 3 post inoculation = 500 mM BHTC, 4 mL per plant; week 4 post inoculation = 750 mM BHTC, 4 mL per plant; and week 5 post inoculation = 1 mM BHTC, 4 mL per plant. Plants were evaluated 5 weeks post inoculation for severity of disease symptoms (leaf chlorosis/wilting and vascular stem discoloration) relative to noninoculated plants (10 BHTC-treated, 10 mock-treated, and 10 untreated plants) using a 0 to 5 rating scale as described previously (Pottorff et al, 2012). One hundred DMSO-treated and 100 BHTC-treated plants were scored individually in each experiment, and statistical significance was determined using x 2 tests of independence.…”

“…One hundred DMSO-treated and 100 BHTC-treated plants were scored individually in each experiment, and statistical significance was determined using x 2 tests of independence. Fot3 was grown and inoculum prepared as described previously (Pottorff et al, 2012). Cowpea-Fot3 experiments were conducted in a greenhouse with day temperatures up to 35°C and night temperatures down to 16°C.…”

Evaluation of Cowpea Genotypes for Resistance to <i>Fusarium redolens</i> in Uganda

“…Management of root rots is done following an integrated approach employing genetic resistance, cultural practices and chemical application [6] [7] [8]. While there are no known varieties resistant to cowpea root rots, fungicide application is associated with negative environmental, economic and health concerns that cannot be ignored [8].…”

“…While there are no known varieties resistant to cowpea root rots, fungicide application is associated with negative environmental, economic and health concerns that cannot be ignored [8]. Therefore, genetic resistance is the most sustainable strategy for managing root rots.…”

Fusarium species associated with grain sorghum and mungbean in Queensland

“…It is not clear how the pathogen infects mungbean, although the cowpea pathogen, F. oxsporum f. sp. tracheiphilum, is thought to invade the root system via the vascular tissue, resulting in wilt, leaf chlorosis, and stunting of the entire plant (Pottorff et al, 2012). According to , in mungbean seedlings, leaves wilt and the stem may start to brown as a basal rot develops.…”