Introgression of resistance to Rotylenchulus reniformis into Meloidogyne incognita resistant upland cotton

Abstract

Reniform nematodes, Rotylenchulus reniformis, can cause losses in cotton yield as high as 60% (Robinson; Yik and Birchfield). High levels of resistance to this nematode has not been reported in Gossypium hirsutum, although Gossypium barbadense accession TX110 has shown a moderate level of resistance to R. reniformis (Yik). TX110 was crossed with M315, G. hirsutum, a root-knot (Meloidogyne incognita) resistant line, and screened in order to identify F[2:3] progeny resistant to both reniform and root-knot nematodes in a G. hirsutum background. F2 plants produced from TX110/M315 were screened for early maturity since the TX110 parent is photoperiodic. A selection of greenhouse-grown F[2:3] plants were inoculated with 15,000 eggs/pot of R. reniformis and screened using eggs counts collected from root and soil samples 10 weeks after inoculation. Resistant plants were transplanted and inoculated with 19,500 eggs/pot of M. incognita. Approximately 29 weeks after inoculation, nematode eggs were extracted from the roots. These egg counts produced an even distribution not typical of a trait controlled by two genes as reported for root-knot resistance. The eggs were then hatched to ascertain that the eggs were in fact R. reniformis, indicating the reniform populations remaining on the roots following transplanting were able to out-compete M. incognita. The plants that showed low egg densities in the reniform screening also showed low egg densities from the root-knot inoculation where reniform thrived. F[3:4] plants derived from these F[2:3] reniform resistant plants are currently being screened for root-knot resistance. Additional F[2:3] plants were screened for resistance to M. incognita in a manmade sandy soil at the Texas A&M Research Farm. Harvesting and rating the roots showed insufficient levels of galling on susceptible lines to screen for resistance, so a subset of 200 plants was transplanted to a greenhouse and re-inoculated with M. incognita to be screened at a later date. Results suggest that it is possible to combine resistance to reniform and root-knot nematodes by using interspecific hybridization with selection.