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CROP BREEDING & GENETICS

Identification of Molecular Markers Associated with Root-Knot Nematode Resistance in Upland Cotton

^a Dep. of Plant and Environ. Sci., Box 30003, New Mexico State Univ., Las Cruces, NM 88003
^b USDA-ARS, Southern Regional Research Center, 1100 Robert E. Lee Blvd., New Orleans, LA 70124
^c Cotton Incorporated, 6399 Weston Pkwy., Cary, NC 27513
^d Dep. of Nematology, Univ. of California, Riverside, CA 92521-0415

^* Corresponding author (jinzhang{at}nmsu.edu).

Cotton breeding for resistance to root-knot nematode (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood] is hindered by the lack of convenient and reliable screening methods for resistant plants. The identification of molecular markers closely linked to RKN resistance will facilitate the development of RKN resistant cultivars through marker-assisted selection (MAS). Our objective was to identify and develop new DNA markers that are associated with RKN resistance in cotton. Using three pairs of near-isogenic (NIL) resistant (R) and susceptible (S) lines, two AFLP markers, two RAPD markers, and three RGA markers were identified to be polymorphic between the NIL-R and NIL-S lines. One RAPD marker was converted into a sequence-tagged site (STS) marker. In an F₂ population of ‘ST 474’ x ‘Auburn 634 RNR’, the two RAPD markers and the STS marker were mapped to the same linkage group containing several markers that were previously reported to be linked with the RKN resistance gene rkn1 on chromosome 11 in ‘Acala NemX’. All these markers were found to be associated with a major RKN resistance gene, presumably Mi₂ in the resistant line Auburn 634 RNR, suggesting that rkn1 and Mi₂ are either allelic or closely linked. In addition, no susceptible recombinants were found in a resistance screen of 200 F₂ plants from the cross Acala NemX x Auburn 634 RNR. The utility of the two RAPD markers and the converted STS marker were evaluated using 23 R and 8 S germplasm lines. The RAPD and STS markers, along with other previously reported markers associated with RKN resistance will be useful in germplasm screening, MAS for RKN resistance, and map-based cloning for RKN resistance genes.

Abbreviations: AFLP, amplified fragment length polymorphism • CAP, cleaved amplified polymorphism • MAS, marker-assisted selection • NIL, near isogenic line • RAPD, random amplified polymorphic DNA • RGA, resistance gene analogue • RKN, root-knot nematode • SSR, simple sequence repeat • STS, sequence-tagged site.