Development of Reniform Nematode Resistance in Cotton through Molecular Breeding

The reniform nematode (RN), Rotylenchulus reniformis Linford & Oliveira, has emerged as one of the major pests of cotton contributing to severe yield losses in United States. Discontinuation of nematicides such as TEMIK® has necessitated development of varieties with host RN resistance. Although RN resistance had been previously identified in diploid K-genome species, Gossypium longicalyx, and in Inca GB713, a tetraploid wild Mexican race belonging to G. barbadense species; the lack of commercial cotton cultivars with natural host resistance to reniform nematode is currently limiting cotton yield gain. Previously, QTL regions associated with RN resistance from the resistant sources were identified using Simple Sequence Repeat (SSR) markers. More recently, single nucleotide polymorphisms (SNPs) are the marker of choice for high throughput, automatable screening of large populations. Here we report SNP markers associated with RN resistance from the Inca GB713 source. An interspecific mapping population was constructed by crossing an upland RN susceptible genotype with Inca GB713 and was used for phenotyping, genotyping and trait mapping purposes. Two QTLs, a major QTL on chromosome 21 and a minor QTL on chromosome 18 were identified and had explained up to 37% of total phenotypic variation in RN resistance. Leveraging Marker Assisted Selection (MAS) of these closely linked SNP markers and evaluation for linkage drag, the development of improved commercial cultivars with RN resistance was expedited through molecular breeding.