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Genetic Mapping of Fusarium oxysporum f.sp. tracheiphilum Race 3 and Race 4, Macrophomina phaseolina Resistance and Other Traits in Cowpea (Vigna unguiculata [L.] Walp).


Cowpea (Vigna unguiculata) is a legume crop which is grown in many warm regions around the world. Genomic resources have been developed for cowpea which has enabled the identification of QTL and candidate genes which can be utilized in trait improvement.

Fungal diseases cause significant constraints to cowpea yield. Fusarium oxysporum f.sp. tracheiphilum (Fot) race 3 and race 4 cause vascular wilt disease and are problematic in California. Genetic mapping identified the Fot3-1 locus which confers resistance to Fot race 3 in the CB27 x 24-125B-1 population. Fot3-1 was identified on BAC clone CH093L18, which carries leucine-rich repeat serine/threonine protein kinases. QTLs were identified which confer resistance against Fot race 4. Fot4-1 was identified in the IT93K-503-1 x CB46 population and Fot4-2 was identified in the CB27 x 24-125B-1 and CB27 x IT82E-18(Big Buff) populations. The syntenic loci for Fot4-1 and Fot4-2 were examined with Glycine max, where several disease resistance candidate genes were identified.

Macrophomina phaseolina is a fungal pathogen which causes diseases under high temperatures and drought-stress. QTLs, Mac-10, Mac-11, Mac-12 and Mac-13, were identified in the Sanzi x Vita 7 population. The Mac-11 locus was positioned within BAC clone CH038D17 where an auxin response factor was present. Mac-13 was identified within BAC clones CH062O11 and CH069K06, where an auxin-responsive GH3 family protein was present.

Leaf morphology was studied in the cowpea RIL population, Sanzi x Vita 7, in which a QTL was identified for leaf shape, Hls. High co-linearity was observed for the syntenic Hls region in Medicago truncatula and Glycine max where EZA1/SWINGER genes were present.

Heat-induced browning of seed coats is caused by high temperatures which discolors the seed coats of cowpea. Three QTL, Hbs-1, Hbs-2, and Hbs-3, were identified using cowpea RIL populations IT93K-503-1 x CB46 and IT84S-2246 x TVu14676. Hbs-1 was identified in BAC clone CM018C23 where ethylene forming enzymes were present. Hbs-3 was identified in BAC clones CH047M01 and CM014K16 where ACC synthase genes were present.

Practical outcomes from these studies are the identification of molecular markers which can be used in a Marker Assisted Selection breeding scheme, which should expedite variety development for cowpea.

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