In an article entitled, “Re-evaluation of the inheritance for root-knot nematode resistance in the Upland cotton germplasm line M-120 RNR,” published in the April, 2014 issue ofTheoretical and Applied Genetics revealed two epistatic QTLs conferring root-knot nematode resistance, the lead author, Yajun He and his seven associates report a second major QTL for root-knot nematode resistance in the highly resistant Upland cotton (Gossypium hirsutum) line M-120RNR showing epistasis between two resistant QTLs with different mechanisms conferring resistance.
In an earlier study, the authors identified a major QTL on Chromosome 11 associated with resistance to root-knot nematode in the M-120 RNR Upland cotton line of the Auburn 623 RNR source. In the subsequent article the authors re-evaluated the genetics of the resistance to root-knot nematode in the M-120 RNR × Pima S-6 population by linkage mapping. In the subsequent study they used recently published SSR markers. The QTL analysis revealed two major regions associated with the resistance phenotype. In addition to the QTL previously identified on Chromosome 11 (qMi–C11), a major QTL was identified on Chromosome 14 (qMi–C14). The two resistance loci located on the qMi–C11 and the qMi–C14 locus, originated respectively from the Clevewilt parent, while the qMi–C14 locus derived its origin from the other resistant parent, Mexico Wild Jack Jones. The results of the later studies suggest that the qMi–C11 locus has a much stronger effect on root gall suppression than egg production, while the qMi–C14 locus had a stronger effect on egg production than galling. The results also suggest that the transgressive segregation observed in the development of Auburn 623 RNR was due to the pyramiding of at least two main effect QTLs as well as an additive-by-additive epistatic effects between the two resistant loci. The SSRs markers tightly linked to theqMi–C11 and qMi–C14 loci will greatly facilitate the improvement of RKN resistance in cotton via marker-assisted breeding.