Investigations of Pasteuria and the Root-Lesion Nematode Pratylenchus penetrans in Soils Collected from Certified Organic Farms in the Mid-Atlantic United States

Occurrence of lesion nematodes and Pasteuria, an obligate bacterial parasite, was surveyed in 34 soils collected from certified organic farms in the Mid-Atlantic United States. Pasteuria endospores were observed on Pratylenchus crenatus in six of 22 soils. Population density of Pratylenchus in soils lacking signs of Pasteuria correlated positively with soil pH, cation exchange capacity, and concentration of phosphorus pentoxide and calcium. Pasteuria was detected on Pratylenchus in nematode suppressive soils at the West Virginia University Organic Research Farm. Interactions between Pasteuria and Pratylenchus penetrans were studied in two laboratory bench-top experiments. Soil treatment effects on reproduction of Pratylenchus penetrans on green bean (Phaseolus vulgaris) cv. Jade in soils with Pasteuria were compared. Sterile and non-sterile Organic Research Farm soil treatments were planted with Phaseolus vulgaris cv. Jade and three of four treatments were inoculated with Pratylenchus penetrans. Mean population densities of Pratylenchus were significantly different among soil treatments (P \u3e 0.0001) and Pasteuria endospores were observed on Pratylenchus crenatus from a control treatment. Twelve soils from the survey samples, six with and six without Pasteuria endospores detected on lesion nematodes, were used to compare eight soil treatment combinations in three randomized blocks. Treatment combinations consisted of soil type, time of harvest, presence of Pasteuria, and lesion nematode inoculation. Populations of Pratylenchus penetrans decreased in both Pasteuria soil treatments (P \u3e 0.03). Population densities of Pratylenchus were not significantly different among soils with and without Pasteuria at the two-week harvest period (P \u3e 0.17). At the 8-week harvest, lesion nematode population densities were significantly lower in soils with Pasteuria than in soils without Pasteuria (P = 0.09). Results suggest that reproduction of Pratylenchus penetrans on Phaseolus vulgaris cv. Jade is lower in soils with Pasteuria detected on lesion nematodes than in soils without Pasteuria detected on Pratylenchus