In warm upland farming areas of Japan sweet potatoes are cultivated in fields with diverse conditions. Differences in field conditions may influence the occurrence of plant-parasitic nematodes. We investigated plant-parasitic nematode fauna, field conditions, and their relationships in a typical warm upland farming area of southern Kyushu, Japan. Plant-parasitic nematodes, primarily Meloidogyne spp. and Rotylenchulus reniformis, were frequently detected as already reported. The density of R. reniformis was higher in the land category,“ upland” than in “paddy” fields. A positive correlation was detected between the degree of field dryness, estimated by topography, and R. reniformis density. Andosols typically exhibit a higher phosphate adsorption coefficient compared to lowland soils, and positive correlations were observed between this coefficient and both the densities of Meloidogyne spp. and R. reniformis. These results suggest that soil properties and field dryness may be important factors to consider in future nematode control strategies.

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Bacterial endosymbionts significantly affect the ecology, evolution, and development of the host by manipulating host physiology to enhance host fitness. Wolbachia and Cardinium species are among the most widespread endosymbionts, infecting a range of hosts including animal-, insect-, and plant-parasitic nematodes, arachnids, and insects. Previous research has shown that some plant- and animal-parasitic nematodes harbor Wolbachia and/or Cardinium. While these studies have suggested a range of Wolbachia and Cardinium species in plant-parasitic nematodes, large-scale screening in nematodes is rare. We report a novel interaction between Cardinium and fungal-feeding nematodes. Polymerase chain reaction (PCR) screening using primers specific for Wolbachia and Cardinium was conducted in 182 strains of 27 nematode species. While Wolbachia was not detected, Cardinium-specific PCR amplicons were obtained from three strains of Aphelenchus avenae. Phylogenetic analysis indicated that these Cardinium strains were distinct from previously described strains. However, fluorescence in situ hybridization analysis did not detect Cardinium in the gonads. Genome analysis showed low abundance of Cardinium in the nematode. Moreover, Southern blot analysis showed the Cardinium sequence is not derived from A. avenae genome, suggesting an extremely low abundance of Cardinium exists in A. avenae cells. Desiccation tolerance assays showed no significant difference in survival between Cardinium-positive and -negative strains, although Cardinium-positive strains tended to have higher survival rates.

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Pratylenchus spp. are among the pests most frequently detected during quarantine inspections of ornamental trees. Ornamental trees are treated with nematicides to eliminate Pratylenchus before export from Japan. Three nematicides, abamectin, fosthiazate and imicyafos, have been registered for use against Pratylenchus in ornamental trees; however, their effects on Pratylenchus eggs have not been investigated. We observed the hatching rate of P. penetrans eggs after immersion in these nematicides. Benomyl, fenitrothion and fluopyram were tested for comparison. Treatment with abamectin, fosthiazate and fluopyram solution for 24 h at 25°C significantly decreased the egg hatching rate; the lowest (5.9%) in fosthiazate compared to 52.3% in the control. However, when eggs were immersed at 10°C the hatching rates of fosthiazate and fluopyram treatment groups were significantly higher than those at 25°C. Eggs treated with abamectin, fosthiazate, fenitrothion and fluopyram concentrations 10 times lower than the registered concentrations for 14 days at 10°C significantly decreased the hatching rates; however, the rate was 29.0% (fluopyram) or more compared to 49.2% in the control. These results suggest that the nematicide effect on eggs may be limited under winter treatment conditions commonly used for ornamental trees.

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Stunt nematodes detected in three fields of komatsuna (Japanese mustard spinach) in Tokyo were identified as Tylenchorhynchus zeae based on morphological observations, sequences of D2/ D3 fragments of the 28S rRNA gene, the internal transcribed spacer region of rDNA and partial 18S rRNA gene. The PCR-RFLP analysis of the 48 samples showed the same digestion pattern and did not indicate the occurrence of multiple species. The pathogenicity of this nematode to komatsuna remains to be elucidated.

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