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Project description

Life Cycle and Population Dynamics of Pasteuria sp., a Host-Specific Parasite of the Sting Nematode. (99BC003)
Program UC IPM competitive research grants program
Principal
investigator 		J.O. Becker, Nematology, UC Riverside
Host/habitat Turfgrass; Corn
Pest Sting Nematode Belonolaimus longicaudatus
Disciplines Nematology, Soil Microbiology
Beneficial
organism 		Pasteuria sp.
Review
panel 		Biological Controls
 Start year (duration)  1999 (Three Years)
Objectives Describe life cycle and monitor host-parasite interactions of the sting nematode and Pasteuria sp. strain S1 in gnotobiotic culture.

Determine optimal growth and survival requirements of Pasteuria sp. S1 through in vitro and greenhouse studies.

Monitor population dynamics, dissemination and efficacy of parasitism of Pasteuria sp. in augmentation sites on two sting nematode-infested golf courses.

Final report Bacteria of the genus Pasteuria have often been cited as the best candidates for biological control agents against plant-parasitic nematodes. The endospore-forming bacteria are effective parasites of many nematode species and they are highly tolerant to heat, desiccation and pesticides. Approximately 10 years ago, a previously undiscovered Pasteuria species (S-1) was found to attach to and parasitize Belonolaimus longicaudatus, the sting nematode. This nematode has a wide host range and a considerable damage potential. Its distribution in California is currently limited to a few golf courses in the Coachella Valley but it is likely to spread with time into agricultural areas. In contrast to the ubiquitous root-knot nematode parasite P. penetrans, S-1 has so far only been found in Florida and it significantly differs morphologically and genetically from previously described species. The key to study the bacteria's life cycle was to devise a transparent culture system that allowed frequent microscopic observations with little disturbance. As both the nematode and the bacteria require their respective host for feeding and reproduction, they were raised aseptically together with corn roots on plant tissue culture media. After 45 days at 28C, one third of the nematodes were filled with mature S-1 endospores. Newly formed endospores released from nematodes attached to all the sting nematode's juvenile stages and adults. Bacterial growth was observed in third and fourth juvenile stages and in adults of the sting nematode. The potential dissemination of Pasteuria S-1 after intentional release was studied at two field sites in sting nematode-infested golf courses in the Coachella Valley. The percent of sting nematodes with bacterialspores attached increased at the Pasteuria-infested site from approximately 48% after 3 months to about 75% after 11 months at one golf course. In the other trial at a second golf course, the population of nematodes with spores attached increased from approximately 24% to 45% during the same time period. The bacteria were disseminated slowly by the movement of the nematodes. After approximately 11 months and at both locations, the populations of the sting nematode in Pasteuria-infested plots dropped significantly below the level of the noninfested checks.

Third-year
progress 		The recently discovered bacterium Pasteuria sp. strain S-1 is an obligate, mycelial, endospore-forming parasite that so far has been found to attach to and parasitize only the sting nematode Belonolaimus longicaudatus. Compared to the common root-knot nematode parasite P. penetrans, S-1 significantly differs in morphology and is nearly double in size. S-1 has only 96% or less homology to 16S rRNA genes from previously described Pasteuria species. These findings suggest that S-1 is a previously undescribed species. Its potential dissemination was studied for 1-1/2 years at two field sites in sting nematode-infested golf courses in the Coachella Valley. The percent of nematodes with bacterial spores attached increased at the Pasteuria-infested site from approximately 48% after 3 months to about 75% after 11 months at one golf course. In the parallel trial at another golf course the population of nematodes with spores attached increased from approximately 24% to 45% during the same time period. The bacteria were disseminated by the movement of the nematodes. After approximately 11 months and at both locations, the populations of the sting nematode in Pasteuria-infested plots dropped significantly below the level of the non-infested checks.

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