Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2017
Publication Date: 1/31/2017
Citation: Wubben, M., McCarty Jr, J.C., Jenkins, J.N., Callahan, F.E., Deng, D.D. 2017. Individual and combined contributions of the Renbarb1, Renbarb2, and Renbarb3 quantitative trait loci to reniform nematode (Rotylenchulus reniformis Linford & Oliveira) resistance in Upland Cotton (Gossypium hirsutum L.). Euphytica. 213:1-9.
Interpretive Summary: The reniform nematode is a very serious pathogen of Upland cotton that is grown throughout the southeastern United States and Texas. Recently, Upland germplasm lines were released that contained resistance to reniform nematode derived from the wild accession GB713. This resistance was previously determined to be controlled by three quantitative trait loci (QTLs) that were named Renbarb1, Renbarb2, and Renbarb3. To further characterize this resistance, isolines were developed that contained each QTL by itself and in every possible combination with one another. Reniform nematode infection assays were performed and reniform egg mass formation, total reproduction per gram root, and eggs per egg mass were determined. For both egg mass formation and total reproduction, we discovered that Renbarb1 was a false positive QTL in the earlier mapping study and that the bulk of resistance was conferred by Renbarb2. When Renbarb3 was combined with Renbarb2, the isoline showed a level of resistance that was equivalent to the GB713 parent. Nematode fecundity, i.e., eggs per egg mass, did not differ between any of the resistant isolines and susceptible controls. These experiments demonstrate that reniform nematode resistance derived from GB713 is controlled by only two QTLs and that the resistance manifests as an inability of the infective nematodes to establish a feeding site in the root.
Technical Abstract: The infection of Upland cotton (Gossypium hirsutum L.) by the root parasite Rotylenchulus reniformis (Linford & Oliveira), the reniform nematode, results in massive annual yield losses throughout the southeastern United States and portions of Texas. Resistance to reniform nematode was identified in the photoperiodic G. barbadense accession GB713. This resistance was transferred to day-neutral G. hirsutum germplasm lines subsequently named M713 Ren1, M713 Ren2, and M713 Ren5 via marker-assisted selection (MAS). Three quantitative trait loci (QTLs) were identified that mediate GB713-derived reniform nematode resistance. Two of these QTLs reside next to each other on chromosome 21 (Renbarb1 and Renbarb2) while Renbarb3 was mapped to chromosome 18. In the present study, reniform nematode reproduction and fecundity was measured for eight G. hirsutum isolines, developed through MAS, that represented every possible combination of Renbarb QTLs. Our data clearly show that the Renbarb1 locus is a false QTL and is dispensable for resistance. We found that reniform nematode resistance equivalent to the GB713 parent was obtained through combination of Renbarb2 and Renbarb3; however, Renbarb2 alone still conferred an approximately 71% reduction in eggs g-1 root compared to the susceptible check. GB713-derived resistance does not affect reniform nematode fecundity but instead appears to manifest as an inability of infective female nematodes to establish in the root early in the infection process. These findings will streamline cotton MAS breeding programs by reducing the number of reniform nematode resistance loci that require tracking in segregating populations.