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Project description

Role of Egg-Parasitizing Fungal Communities in Soil Suppressiveness Against Heterodera schachtii. (99FE027)
Program UC IPM competitive research grants program
Principal
investigator
J.O. Becker, Nematology, UC Riverside
Host/habitat Sugarbeets; Cabbage; Broccoli; Cauliflower; Spinach; Brussels Sprouts; Cole Crops; Canola
Pest Sugarbeet Cyst Nematode Heterodera schachtii
Discipline Nematology
Beneficial
organism
Fusarium sp.
Review
panel
Applied Field Ecology
Start year (duration)  1999 (Three Years)
Objectives Determine the effects of temperature and soil moisture potential on infection of Heterodera schachtii eggs by egg-parasitizing fungi in a suppressive and conducive soils.

Characterize and identify dominant egg-parasitizing fungi in cyst nematode suppressive soil.

Compare frequencies of egg infection in fumigated soil re-infested with the individual or a mixture of fungal antagonists.

Examine nematode antagonistic potentials of soils infested with mixtures of fungal antagonists under greenhouse and field conditions to characterize the fungal community responsible for soil suppressiveness.

Final report In California, losses caused by the beet cyst nematode, Heterodera schachtii, have been estimated to exceed $60 million annually. Pesticide use for the management of this nematode in Chenopodiaceae and Cruciferae crop production becomes increasingly more restricted, expensive, or unavailable. Nematode soil suppressiveness is a natural pest-reducing capacity that is characterized by the inability of a plant-parasitic nematode population to increase despite the presence of susceptible host plants and favorable environmental conditions. At the University of California Agricultural Operations, one field has been known for some years to be highly suppressive to the beet cyst nematode. Formaldehyde as well as fludioxonil reduced soil suppressiveness while PCNB, mefenoxam, and antibiotics were not effective. Cysts of H. schachtii from the suppressive soil were often infested with fungal egg parasites. Bioassays with soils at various temperatures and soil water potentials revealed no clear differences in nematode egg parasitism, although the infection rate dropped with increasing temperature and reduction of soil water potential.Staining fungal hyphae in eggs revealed a higher percentage of parasitism than plating egg suspensions on media. This indicates that nonculturable or slow-growing organisms may be involved in the nematode population suppression. While many cysts contained parasitize eggs, those completely filled often contained fungal hyphae with chlamydospores and frequently showed an orange-reddish stain. Isolations on agar yielded predominantly Fusarium oxysporum and Dactylella sp. A microtube assay with young cysts confirmed the parasitic nature of both fungal groups. Various other developmental nematode stages were observed to be parasitized. While predation of soil-dwelling nematode stages such as second-stage juveniles and adult males frequently occurs, population suppression can be attributed primarily to the effects of fungal parasitism of females, males, and eggs.

Third-year
progress
In California, the losses in Chenopodiaceae and Cruciferae crop production due to the beet cyst nematode amount to more than $60 million per year. As pesticide use for the management of this nematode becomes increasingly more restricted, expensive, and unavailable, other forms of control strategies must be pursued. Nematode suppressiveness is a natural pest-reducing capacity of a soil that is characterized by the inability of a nematode pest population to increase despite the presence of susceptible host plants and favorable environmental conditions. A field at the UCR Agricultural Operations was identified as highly suppressive to the beet cyst nematode. Various developmental stages of this nematode were found to be parasitized by fungi. While predation of soil-dwelling nematode stages such as second-stage juveniles and adult males frequently occurs, population suppression can be attributed primarily to the effects of fungal parasitism of females, males, and eggs. Formaldehyde as well as fludioxonil reduced soil suppressiveness while PCNB and mefenoxam were not effective.

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