The clover cyst nematode(Heterodera trifolii)infects white clover(Trifolium repens)in pasture throughout New Zealand, reducing plant growth and nutrition. The preferred control method for both economic and ecological reasons is to breed resistant cultivars, with resistance measured as a reduction in cysts/g of root dry weight. Many New Zealand and overseas white clover seed lines and cultivars were screened for resistance. There were highly significant differences between lines for number of cysts, root weight, and cysts/g of root dry weight. Selected genotypes were re#x2010;screened using five stolon tips per genotype, and the results were correlated with the first screening. There were high correlations 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 forH. trifoliiresistance in the Netherlands. There were no immune plants, but the results and the calculated broad sense heritabilities indicate that breeding for resistance is possible.
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