Population Dynamics of Dactylella oviparasitica and Heterodera schachtii: Toward a Decision Model for Sugar Beet Planting

摘要

A series of experiments were performed to examine the population dynamics of the sugarbeet cyst nematode, Heterodera schachtii, and the nematophagus fungus Dactylella oviparasitica.After two nematode generations, the population densities of H.schachtii were measuredin relation to various initialinfestationdensities of both D.oviparasitica and H.schachtii.In general, higher initial population densities of D.oviparasitica were associated with lower ?nal population densities of H.schachtii.Regression models showedthattheinitialdensitiesofD.oviparasiticawereonlysigni?cantwhenpredictingthe?naldensitiesofH.schachtiiJ2andeggsas well as fungal egg parasitism, while the initial densities of J2 were signi?cant for all ?nal H.schachtii population density measurements.We also showed that the densities of H.schachtii-associated D.oviparasitica ?uctuate greatly, with rRNA gene numbers going from zero in most ?eld-soil-collected cysts to an average of 4.24 x 108 in mature females isolated directly from root surfaces.Finally, phylogenetic analysis of rRNA genessuggestedthat D.oviparasitica belongs to a cladeof nematophagous fungi thatincludesArkansas Fungus strain L (ARF-L) and that these fungi are widely distributed.We anticipate that these ?ndings will provide foundational data facilitating the development of more effective decision models for sugar beet planting.