Residual-resistance effect of two known QTLs in cotton genotypes on Meloidogyne enterolobii reproduction

Summary Meloidogyne enterolobii is not described as a major concern in cotton production, but a new race of this nematode, recently reported in Brazil and the USA, can cause damage to this important crop. Genetic resistance is a promising approach to manage root-knot nematodes (RKN). This study aims to identify in cotton germplasm sources of resistance to M. enterolobii that exhibit resistance to M. incognita . In this study, 18 accessions including Gossypium hirsutum (Upland cotton), G. barbadense (Pima cotton), interspecific hybrids, and G. arboreum were examined for their susceptibility or resistance to M. enterolobii . The experiment involved eight plants of each genotype under glasshouse conditions and was repeated at two different times. The inoculations were made with 10 000 M. enterolobii eggs and, after a period similar to field conditions (120 days), the following variables were evaluated: gall index, egg mass index, total number of eggs (g root) − 1 and the reproduction factor (RF). The susceptible control, ‘FM 966’, displayed high reproduction factor (RF: 86.88-102.20) in both experiments, indicating the aggressiveness of the M. enterolobii cotton population (race 2). Upland genotypes and Upland×Pima hybrids exhibited resistance levels ranging from moderate partial resistant (MPR) to partial resistant (PR), and all G. barbadense genotypes were classified as susceptible, except ‘Tanguis’ and ‘Pima California’, which were MPR. The Gossypium arboreum genotype was considered susceptible in both experiments. Despite the virulence of M. enterolobii race 2, some cotton genotypes used in our experiments with RKN resistance QTLs (quantitative trait loci, qMi-C11 and qMi-C14 ) demonstrated a significant partial resistance ( ca 80%) in reducing the final high nematode population after 120 days of inoculation. Our study highlights the importance of selecting residual resistance effect to Meloidogyne spp. on cotton after more nematode cycles to show the final nematode population reduction to mitigate the impact of M. enterolobii on the cotton crop.