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Title:   Author  item
                                            WANG, C. - UNIV. OF CA-RIVERSIDEitem
                                            Ulloa, Mauricioitem
                                            ROBERTS, P. - UNIV. OF CA-RIVERSIDE
  Submitted to: Journal of Theoretical and Applied Genetics
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/30/2005
                                    Publication  Date: 2/1/2006
                                    Citation: Wang, C., Ulloa, M., Roberts, P.A. 2006. Identification and mapping of microsatellite markers linked to a root-knot nematode resistance gene (rkn1) in acala NemX cotton (Gossypium hirsutum L.). Theor. Appl. Genet. 112:770-777.Interpretive Summary: Host-plant resistance is the most economic and effective strategy for root-knot nematode Meloidogyne incognita control in cotton (Gossypium hirsutum L.). This round worm damages cotton directly and also forms a disease complex with the Fusarium wilt pathogen, resulting in severe yield loss in some growing regions in the U.S. The development and/or identification of molecular markers linked to resistance are important for incorporating resistance genes into elite cultivars. Once molecular markers linked to resistance genes are developed and/or identified, wide selection for root-knot nematode resistance in cotton breeding can be achieved through marker-assisted selection (MAS), rather than on morphological selection which is time-consuming, expensive and sensitive to screening conditions. Genetic markers will also enable unique resistance genes to be pyramided in one genotype or to be deployed individually. Such strategies can promote the durability of resistance because M. incognita is known to become virulent through selection pressure. Two hundred and sixty-eight markers covering most of the cotton genome were evaluated to determine which markers were associated with nematode resistance.  One molecular marker, designated CIR316 was very closely associated and two others were more loosely associated but still useful. CIR316 will be useful for detecting the presence of the resistance gene in a variety of populations and will be used as a tool in marker-assisted selection. The marker will also be useful to develop cultivars resistant to multiple pathogens.
                                Technical Abstract: Host-plant resistance is the most economic and effective strategy for root-knot nematode Meloidogyne incognita control in cotton (Gossypium hirsutum L.). Molecular markers linked to resistance are important for incorporating resistance genes into elite cultivars. To screen for microsatellite markers (SSR) closely linked to root-knot nematode resistance gene rkn1 in G. hirsutum cv. Acala NemX, F1, F2, BC1F1 and F2:7 recombinant inbred lines (RILs) from intraspecific crosses between Acala NemX and a closely related susceptible cv. Acala SJ-2, and an F2 from a G. barbadense cv. Pima S-7 x G. hirsutum cv. Acala NemX interspecific cross were used. Screening of 268 SSR markers, which cover all known identified chromosomes and most linkage groups of cotton, was performed by bulked segregant analysis, revealing informative SSRs. The informative SSRs were then mapped on the above populations. One SSR marker CIR316 was identified tightly linked to the resistance gene rkn1 in Acala NemX with an estimated distance of 2.1 to 3.3 cM depending on the population used. Additional markers, including BNL1231 with loose linkage to rkn1 (map distance 25.1 cM to 27.4 cM), BNL1066 and CIR003 allowed the rkn1 gene to be mapped to cotton linkage group A03. The co-dominant marker CIR316 tightly linked to rkn1 in Acala NemX will be useful for detecting the presence of this resistance gene in a variety of populations as a tool in marker-assisted selection. Fine mapping of rkn1 will expedite gene cloning and incorporation of the resistance gene into cultivars with good crop characteristics and also aid in developing cultivars resistant to multiple pathogens.


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