Variation in white clover for root-knot nematode resistance

Root-knot nematode (Meloidogyne sp.) reduces growth and nutrition of white clover (Trifolium repens L.). Breeding resistant cultivars is the preferred control method. A range of overseas and New Zealand white clover lines was screened for resistance, measured as a reduction in the number of galls per root size. Highly significant differences between white clover lines were found, although no plants were immune. There was variation in both gall numbers and root size, and root size was a major factor determining the galls/root ratio. The most resistant genotypes generally were from larger-leaved lines, whereas the most suceptible genotypes generally were from smaller-leaved lines. Resistant genotypes (and some susceptible genotypes) were re-screened, some twice, using five clonal propagules per genotype. While there were significant correlations between the re-screens for galls, roots, and galls/root, the values showed that repeatability was low. Comparisons with other nematode and clover species are made.