Search for Virulence in Reniform Nematodes

In recent years there have been several sources of resistance to the reniform nematode Rotylenchulus reniformis identified within the Gossypium germplasm collection. Breeding efforts are in progress to introgress this resistance into high yielding G. hirsutum genotypes. As this resistance is deployed there is concern about the durability of the trait. Genetic resistance is vulnerable to virulence in the nematode populations were virulence is defined as the ability of the selected nematode populations to overcome the resistance phenotype. Virulence is a common trait among the cysts nematodes (Globodera and Heterodera spp.) but is relatively rare among the root-knot nematodes (Meloidogyne spp.). Currently there are no data on the occurrence of virulence within reniform nematode populations. In the present study, 49 isolates of R. reniformis collected from six cotton fields were tested for virulence on three sources of resistance. The resistance were those derived from G. lonicalyx and introgressed into G. hirsutum, and resistance from G barbadense genotypes TX110 and GB73, also introgressed into G. hirsutum. In greenhouse tests, replicated individuals of each resistant cotton genotype and the susceptible DP90 were inoculated separately with ca 1,000 to 2,000 mixed life stages of the reniform isolates. Nematode populations were measured after ca. eight weeks by extracting vermiform stages from the soil using a modified Baermann tray. No reniform isolate was identified that exhibited specific virulence on any of the resistant cotton genotypes tested. These data suggest that virulence was not present among the isolates tested.