Genetic diversity for root-knot nematode resistance in white clover and related species

Abstract

A total of 237 Plant Introduction in eleven Trifolium species were evaluated for resistance to Meloidogyne arenaria (Neal) Chitwood race 1, M. hapla Chitwood, M. incognita (Kofoid & White) Chitwood race 3, and M. javanica (Treub) Chitwood. Plants were infected with 1500 nematode eggs collected from 'Rutgers' tomato (Lycoperiscon esculentum Mill.) roots with 0.5% NaOCl. Ratings of galling severity and egg mass production were assigned to each plant 8 wk after inoculation. Host plant reaction was classified as immune, highly resistant, resistant, moderately resistant, intermediate, moderately susceptible, susceptible, and highly susceptible according to the resistance index $RI{\text{ = }}\sqrt {{\text{(gall}}^{\text{2}} {\text{ + egg}}^{\text{2}} {\text{)}}}$. More than 95% of 171 white clover accessions were moderately to highly susceptible to all four nematodes species. The best white clover accessions were only moderately resistant to either M. arenaria (PI 291843 and PI 306286) or M. hapla (PI 100250 and PI 204930). Accessions with moderate resistance or resistance to root-knot nematodes were found among relatives of white clover, with T. ambiguum M. Bieb. exhibiting the greatest resistance level. Among the other Trifolium species evaluated, T. carolinianum Michx. PI 516273 was immune or highly resistant to all four nematode species while accessions of T. hirtum All. showed a wide range of reaction to root-knot nematodes. Identified germplasm of white clover relatives with resistance to root knot nematodes should be useful for the selection of parents in white clover breeding programs.