VARIATION IN WHITE CLOVER FOR RESISTANCE TO CLOVER CYST-NEMATODE

The clover cyst nematode (Heterodera trifolii) infects white clover (T rifolium repens) in pasture throughout New Zealand, reducing plant gro wth and nutrition. The preferred control method for both economic and ecological reasons is to breed resistant cultivars, with resistance me asured as a reduction in cysts/g of root dry weight. Many New Zealand and overseas white clover seed lines and cultivars were screened for r esistance. There were highly significant differences between lines for number of cysts, root weight, and cysts/g of root dry weight. Selecte d genotypes were rescreened using five stolen tips per genotype, and t he results were correlated with the first screening. There were high c orrelations between the number of cysts/plant and cysts/g of root dry weight for all screenings. Two Italian Ladino cultivars were generally among the most resistant lines, as was a line bred for H. trifolii re sistance in the Netherlands. There were no immune plants, but the resu lts and the calculated broad sense heritabilities indicate that breedi ng for resistance is possible.