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Title:   Author  item
                                            ROBERTS, P. - UC-RIVERSIDE, CAitem
                                            Ulloa, Mauricioitem
                                            WANG, C. - UC-RIVERSIDE, CA
  Submitted to: World Cotton Research Conference Proceedings
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 10/30/2007
                                    Publication  Date: 12/1/2008
                                    Citation: Roberts, P.A., Ulloa, M., Wang, C. 2008. Host Plant Resistance to Root-Knot Nematode in Cotton. World Cotton Res. Conf. Lubbock, TX (Proc) paper no. 1319.Interpretive Summary: The root-knot nematode (RKN) is a small parasitic worm that injures roots of several types of crop plants. In cotton, host-plant resistance can be an economic and highly effective method for root-knot nematode control. In this manuscript, we present an overview of RKN host plant resistance, discuss gene relationships, and the use of molecular markers in developing RKN-resistant cottons. Nematode resistance can protect cotton plants from direct injury and yield losses from nematode infection, and can also protect against the root-knot nematode-Fusarium wilt disease complex caused by combined nematode and fungus infection. In addition, resistance in cotton suppresses soil nematode populations, thereby protecting other susceptible crops grown in rotation with cotton. Recently, nematode resistance (R) gene mapping in cotton has revealed relationships between resistant cottons and certain molecular markers, and these relationships are useful in the genetic improvement of cotton. Markers of a specific type (microsatellites) linked to RKN resistance in the variety Acala NemX were identified from crosses of different Acala and Pima cotton populations. These microsatellite markers allowed the R gene (rkn1) to be mapped on cotton chromosome 11. Other types of markers also linked to rkn1 were developed for rapid screening to identify resistant RKN cottons. Use of molecular markers can facilitate the mapping of economically important traits, and thus speed efforts to incorporate resistance genes into elite cultivars.
                                Technical Abstract: Host-plant resistance is economic and highly effective for root-knot nematode (RKN) Meloidogyne incognita control in cotton Gossypium hirsutum. Nematode resistance can protect cotton plants from direct injury and crop loss from nematode infection, and can protect against the root-knot nematode-Fusarium wilt disease complex caused by combined nematode and fungus infection. In addition, resistance in cotton suppresses soil nematode population densities, thereby protecting other susceptible crops grown in rotation. Recently, nematode resistance (R) gene mapping in cotton has revealed relationships between resistance sources and linked molecular markers for use in genetic improvement of cotton. Markers are important for the efficiency of incorporating resistance genes into elite cultivars. Microsatellite markers (SSRs) linked to RKN resistance in G. hirsutum cv. Acala NemX were identified using segregating progenies and recombinant inbred lines from intraspecific crosses and an interspecific cross with G. barbadense cv. Pima S-7. Informative SSRs were mapped on the above populations and one co-dominant SSR marker CIR316 was identified as tightly linked (2.1 to 3.3 cM) to a major resistance gene (designated rkn1). Additional markers allowed the rkn1 gene to be mapped to cotton chromosome 11. Other markers linked to rkn1 were developed from AFLP screening and converted to CAPS and SNP markers for high throughput screening. Subsequently, a similar location of the major resistance determinant present in the Auburn source of RKN resistance was reported, and additional non-linked minor QTLs for resistance were identified. Higher levels of resistance in cotton by transgressive segregation were obtained with factors contributed by susceptible parents in intraspecific and interspecific crosses. These gene relationships and use of markers for cotton improvement are discussed.


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