Virulence of Two Isolates of (Guava Root-Knot Nematode) from North Carolina on Cotton Lines Resistant to Southern Root-Knot Nematode () and Reniform Nematode ().

[the guava root-knot nematode (RKN)] is an emerging plant-parasitic nematode that poses a threat to Upland cotton () production in the southeastern United States. Like other RKN spp., has a wide host range and proven ability to overcome resistance sources that have helped protect crops from other spp., including the southern RKN (). In this study we evaluated the virulence of two North Carolina isolates on Upland cotton germplasm lines having resistance quantitative trait loci (QTL) to RKN (M240 RNR, MRk-Rn-1) and/or reniform nematode () (M713 Ren1, MRk-Rn-1) in comparison to their susceptible recurrent parents (DPL61, SG747). Multiple assays using eggs or J2 as inoculum demonstrated that both isolates reproduced equally well on all germplasm lines, producing reproductive factor (RF) values ≥ 6 on the otherwise nematode-resistant lines. Measurements of seedling growth in control and inoculated containers suggested that existing nematode-resistance QTL may offer a level of tolerance to infection that should be further explored in greenhouse and field environments. infection of SG747 and MRk-Rn-1 showed nearly identical stages of symptom and nematode development over a time-course of 24 days. These data demonstrate that existing RKN and RN resistance QTL available in elite cotton varieties to producers are most likely insufficient in preventing yield loss due to and that future research should focus on (i) understanding the -cotton interaction at the molecular level, and (ii) screening novel germplasm collections to identify resistance loci.