|Wang, Congli - University Of California|
|Duong, Tra - University Of California|
|Robert, Philip - University Of California|
Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2017
Publication Date: 11/20/2017
Citation: Wang, C., Ulloa, M., Duong, T., Robert, P. 2017. Analysis of transgressive nematode resistance in tetraploid cotton reveals complex interactions in chromosome 11 regions. Frontiers in Plant Science. 8:1979.
Interpretive Summary: Worms or nematodes such as root-knot nematode (RKN) caused disease in plants and represent constant threats to cotton production. Developing RKN resistant cultivars is an important breeding approach, and developed cultivars are highly effective in preventing crop yield loss from RKN infection. In this study, we investigated how RKN resistance is increased on progeny or breeding lines using different cultivars as parents in multiple-crosses. This enhancement on resistance is also known as transgressive resistance. Transgressive resistance to RKN was found in Upland cotton populations, Gossypium hirsutum resistant NemX x susceptible SJ-2, and Pima by Upland [G. barbadense (susceptible Pima S-7) x G. hirsutum (NemX)] cotton populations. Analyses revealed contributions to RKN infection-resistance associated with a molecular marker (SSR) CIR316 linked to resistance gene rkn1 in NemX on Chromosome 11 in seven populations. In addition, markers closely linked to SSR CIR316 contributed up to 82 percent of resistance to infection (root-galling). Stronger transgressive resistance occurred in later than in early generations in the Upland by Upland crosses than in the Pima by Upland crosses. Transgressive effect on progeny from susceptible parents is possibly provided on the rkn1 resistance region of chromosome 11 by tandemly arrayed allele (TAA) or gene (TAG) interactions contributing to transgressive resistance. Complex TAA and TAG recombination and interactions in the rkn1 resistance region provide a model to study disease and transgressive resistance in complex-polyploid plants, and novel cotton-genotypes for plant breeding.
Technical Abstract: Transgressive segregation in cotton (Gossypium spp.) provides an important approach to enhance resistance to the major pest root-knot nematode (RKN) Meloidogyne incognita. Our previous studies reported transgressive RKN resistance in an intraspecific G. hirsutum resistant NemX x susceptible SJ-2 recombinant inbred line (RIL) population and early generation populations of interspecific G. barbadense (susceptible Pima S-7) x G. hirsutum (NemX). However, the underlying functional mechanisms for this phenomenon are not known. The region of RKN resistance gene rkn1 on chromosome (Chr) 11 and its homoeologous Chr 21 was fine mapped with G. raimondii D5 genome reference sequence. Transgressive resistance was found in the later generation of the RIL population F2:7 Pima S-7 x NemX) and one interspecific F2 (susceptible Pima S-7 x susceptible SJ-2). QTL analysis revealed similar contributions to root-galling and egg-production resistance phenotypes associated with SSR marker CIR316 linked to resistance gene rkn1 in NemX on Chr 11 in all seven populations. In the testcross NemX x F1 (Pima S-7 x SJ-2) marker allele CIR069-271 from Pima S-7 linked to CIR316 contributed 63 percent of resistance to galling phenotype in the presence of rkn1. Similarly, in RIL population F2:8 (NemX x SJ-2), SJ-2 markers closely linked to CIR316 contributed up to 82 percent of resistance to root-galling. These results were confirmed in BC1F1 SJ-2 x F1 (NemX x SJ-2), F2 (NemX x SJ-2) and F2 (Pima S-7 x SJ-2) populations in which up to 44 percent, 36, and 15 percent contribution in resistance to galling was found, respectively. Conclusions: Stronger transgressive resistance occurred in later than in early generations in the intraspecific cross than in the interspecific cross. Transgressive effect on progeny from susceptible parents is possibly provided on the rkn1 resistance region of chromosome 11 by tandemly arrayed allele (TAA) or gene (TAG) interactions contributing to transgressive resistance. Complex TAA and TAG recombination and interactions in the rkn1 resistance region provide a model to study disease and transgressive resistance in polyploid plants, and novel genotypes for plant breeding.