Evaluation of heritability and genotype effects of resistance to reniform nematode (Rotylenchulus reniformis) in an upland cotton (Gossypium hirsutum) recombinant inbred line population derived from MT2468 Ren1

Cotton is the primary source of natural fiber in the world. In the United States, more than 95% of cotton produced is of the Upland type (Gossypium hirsutum L.). The reniform nematode (Rotylenchulus reniformis Linford & Oliveira) is a leading pathogen of Upland cotton that causes significant annual yield losses. Developing Upland cultivars with improved resistance to R. reniformis would be the most economical and sustainable approach to minimize the impact of this pathogen, but more genetic information is needed about resistance to R. reniformis. Genetic association mapping studies are an affordable and efficient approach to identify genetic loci associated with R. reniformis resistance traits. However, a crucial component of association mapping is the evaluation of trait heritability and to unbiasedly predict genotypic values/effects for a large mapping population whose members, in many instances, cannot be phenotyped simultaneously. In this study, we employed an incomplete block design to evaluate R. reniformis resistance traits of 126 recombinant inbred lines (RILs) derived from the cross M240 RNR (susceptible) x MT2468 Ren1 (resistant). The three representative resistance traits were nematode eggs g-1 root (EGR), nematode eggs plant-1 (EPLNT), and nematode reproductive factor (RF). We applied a linear mixed model approach to estimating variance components including heritability and to predicting genotypic effects for all RILs and the parents. The results showed that the group effects equivalent to block effects were significant. The heritability based on four replications for single measurement of EGR, EPLNT, and RF was 82.1%, 78.8%, and 79.9%, respectively. The predicted genotypic effects showed a wider range compared to the parents for all three traits and these predicted genotypic effects were positively skewed, suggesting the possibility that at least two loci mediate R. reniformis resistance in MT2468 Ren1 in an as yet unknown fashion. The results of the present study provide a foundation for future identification of SNPs associated with these R. reniformis resistance traits in MT2468 Ren1.