Graduate Thesis Or Dissertation
 

Relationships of six saprozoic nematodes and a nitrogen-fixing bacterium, Rhizobium japonicum (Kirch.) Buchanan

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  • Relationships of six species of saprozoic nematodes, Pristionchus lheriteiri (Maupas, 1919) Paramonov; Panagrolaimus subelongatus (Cobb, 1914) Thorne, 1937; Cephalobus persegnis Bastian 1865; Pelodera (Rhabditis) lambdiensis (Maupas, 1919) Dougherty, 1953; Rhabditis sp. I and Pelodera chitwoodi (Bassen, 1940) Dougherty, 1955 and a nitrogen-fixing bacterium, Rhizobium japonicum (Kirchner, 1895) Buchanan, 1926 were investigated, These nematodes were found reproducing, feeding on cultures of R. japonicum grown on Rhizobium agar medium but the density of the populations varied, depending on the species of nematode. It was demonstrated that these nematodes could carry the bacteria both in the alimentary canal and on the body surface, The average numbers of bacterial cells carried internally, ranging from 12 cells in Rhabditis sp. I to 9, 034 cells in P. lheriteiri, did not correlate with nematode body size. By contrast, the numbers carried externally, ranging from 100 cells on Rhabditis sp. I to 37, 776 cells on Pelodera chitwoodi, had a direct relationship. The relationship between P. lheriteiri and R. japonicum was studied in detail. The saprozoic nematode, P. lheriteiri, could not survive and reproduce on Rhizobium agar medium containing R. japonicum culture broth or an inoculum that were previously autoclaved or sonicated but only could survive if the food source was a living bacterial suspension. Females of P. lheriteiri were found to carry 2, 622 bacterial cells in the alimentary tract while only 1, 004 cells could be found in males. The bacteria still were viable after they were ingested and defecated by the nematodes. The nodule-forming ability of the bacteria, after passing through nematode alimentary tract, did not change, Bacteria carried internally by the nematode could develop nodules on Lee soybean, Glycine max (Linn.) Merr. , roots in water agar as well as those in suspension. There was no relationship between numbers of nodules and numbers of bacteria-carrying nematodes in any treatment. Nodules were small in size, ranging from 0. 5 - 2. 0 mm in diameter, and few in number per plant. Sixty percent of the soybean plants, including 13 percent in the control treatment which were inoculated with a bacterial suspension, formed nodules on roots 30 days after inoculation. Almost 92 percent of nodules were found on or near plant hypocotyls; only 8 percent of the total nodules were seen deep in the agar medium. This investigation indicates that many kinds of saprozoic nematodes can become carriers and disseminators for an agriculturally beneficial bacterium, R. japonicum. P. lheriteiri, Panagrolaimus subelongatus, Pelodera chitwoodi and Pelodera (Rhabditis) lambdiensis were demonstrated to be efficient bacterial vectors. These nematodes, including Rhabditis sp. I and Cephalobus persegnis could carry the bacteria internally as well as externally but this capability varied with the species of nematode.
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