Observations on resistance in white clover (Trifolium repens L.) to the stem nematode (Ditylenchus dipsaci (Kühn) Filipjev)

Abstract

SummaryThe expression of symptoms of stem nematode reproduction on a total of 53 white clovers (26 cultivars, 14 genepools and 13 introductions from plant collections) was studied in a series of field and glasshouse experiments. Seedlings or stolon-tip cuttings were inoculated with nematodes and the clovers classified by the proportion of plants which developed symptoms. Significant differences were found between varieties although in each test the majority was intermediate between more resistant and susceptible extremes. There was significant positive correlation between tests, in spite of different inoculation methods and different average levels of susceptibility. Very large-leaved cv. Aran was more resistant than most other clovers tested, and small-leaved cv. S. 184 was more susceptible. There was no general correlation of leaf size with reaction to stemnematode. Small-leaved cv. Pronitro was also resistant while several large-leaved cultivars were susceptible. In observations of plants exposed to nematodes over a long period, either by sequential inoculations or through perpetuating latent infections, apparently resistant plants eventually succumbed and supported nematode reproduction. It has not been determined whether this was because selection for virulence in the nematodes had occurred.