Effects of Resistance in White Clover (Trifolium repens) on Heterodera trifolii

Clones of two partially resistant and two susceptible white clover, Trifolium repens, genotypes were exposed to eggs of Heterodera trifolii and nematode development in stained roots measured at 2, 4, 7, 11, 18, 23, and 37 days after inoculation. The differences in development between nematode populations in resistant and susceptible genotypes showed that resistance operated after infection during feeding and development. At 7 days after inoculation, counts of second-stage juveniles did not differ between genotypes, whereas at 37 days more adults had developed in the susceptible than in the resistant genotypes. In a separate experiment, cysts hosted by susceptible genotypes were larger and contained more eggs than those on resistant genotypes so that the product of the values for cysts per plant and for eggs per cyst resulted in a more sensitive measure of resistance than from using cysts per plant alone.