Reproduction of Meloidogyne Hapla and Heterodera Trifolii From Several Sites in New Zealand On Resistant and Susceptible Lines of White Clover

Abstract

The effectiveness of resistance in white clover to a number of populations of Meloidogyne hapla and Heterodera trifolii was investigated to ensure that nematode resistant cultivars of white clover would be useful throughout New Zealand. Inoculum from eight populations of M. hapla and H. trifolii from different sites in the North Island was added to two resistant and two susceptible white clover seed lines; a different quartet of white clover lines was used for each nematode species. Root galls and egg masses of M. hapla and cysts of H. trifolii were counted after one generation of nematode development. Chromosomes of six M. hapla populations were stained and counted. On the lines resistant to M. hapla, fewer galls developed than on susceptible lines for each of the eight populations tested. Overall, the resistant lines had lower numbers of egg masses than the susceptible lines but contained twice as many egg masses per gall. There was not a significant interaction between lines and populations for numbers of galls or egg masses, suggesting that the resistance to M. hapla may be horizontal. Chromosome counts placed the M. hapla populations in Race A. H. trifolii cyst counts of populations from six sites were lower on resistant lines than susceptible lines. The interaction term between varieties and populations was significant, suggesting that the resistance to H. trifolii may be of the vertical type.