Ditylenchus dipsaci Infestation of Trifolium repens. I. Temperature Effects, Seedling Invasion, and a Field Survey

Rates of development of stem nematode (Ditylenchus dipsaci) in white clover (Trifolium repens) seedlings were found to be linearly related to temperature. Basal developmental temperature (T(b)) was 3 degrees C, and the thermal constant (S) for development of gravid adult females from freshly laid eggs was 270 accumulated day-degrees above the T(b). Only 12% at 20 degrees C and 4% at 4 degrees C of the gravid female nematodes inoculated into seedling axils successfully penetrated seedling epidermis. These nematodes slowly migrated within the seedling and after a lag of 5 days at 20 degrees C started to lay eggs. The maximal rate of egg production was temperature-dependent, being 0.8 and 3.1 eggs female(1) day(1) at 10 and 20 degrees C, respectively. Nematodes emigrated rapidly from infested stolons when they were immersed in water, with rates being highest at 25 degrees C and lowest at 4 degrees C. The sensitivity to temperature of many of the parameters that govern nematode population dynamics indicates that climatic changes will have a marked effect upon this host-parasite system. A study of infested stolons from the field indicated that nematode numbers increased up to 3,000 or more before tissue senesence, triggered by nematode damage, caused a mass emigration of nematodes from the stolon.