The nematode genus Actus belonging to the order Mononchida, an important group of predatory nematodes, is rare in the world. Actus salvadoricus Baqri and Jairajpuri, 1974, which had been described from El Salvador, were found from subtropical forest in the northern part of Okinawa Island, Japan. Its morphological observation is made herein and its phylogenetic position is elucidated based on 18S rDNA sequence. A. salvadoricus collected from Okinawa is characterized by having its buccal cavity with a moderately developed dorsal tooth, vertical subventral plates with a single row of denticles arranged as 3:3 or 3:4 or 2:4 on two plates, distinct excretory pore, elongate-conoid ventrally arcuate tail, with tandem caudal glands and terminal spinneret. Based on the nearly complete 18S rDNA sequence data already known and revealed in this work, phylogenetic trees of Mononchina were constructed using parsimony and maximum likelihood algorithms. The results show that the genus Actus forms a sister group with the species of the genus Mylonchulus in the suborder Mononchina, showing the valid status of its taxonomic group.

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When rooted chrysanthemum cuttings were transplanted to pots filled with field soil infested with Pratylenchus kumamotoensis, or autoclaved soil with P. kumamotoensis introduced to the rhizosphere of chrysanthemum, the roots showed dark spots or necrotic lesions that often covered almost the entire circumference of the root, causing constrictions at the lesions. Colonies of the nematodes were observed inside roots near the necrotic lesions. Suppression of nematode populations using several antagonistic plants proven to be effective against northern root-lesion nematode, P. penetrans, were tested in greenhouse experiments using 1/5,000 a Wagner pots. Nematode populations in pots planted with peanut, sweet potato, African marigold, French marigold, Senna occidentalis cv. Habusou, or wild oats Avena strigosa were significantly lower (P = 0.05; Tukey-Kramer test) than populations in pots planted with asparagus, chrysanthemum, and even the unplanted fallow pots. The soil in each pot was then re-transplanted with rooted cuttings of chrysanthemum and the nematode populations 118 days after transplantation were examined to elucidate the sustainability of any nematode suppression observed in the preceding crop. In the peanut and sweet potato cultivation treatments both soil and root populations of P. kumamotoensis were significantly suppressed (P = 0.05; Tukey-Kramer test) to a greater extent than the other treatments tested.

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Soil drench, bare root or seed dip treatments of tomato (Lycopersicon esculentum Mill.) were used to test the control efficacy of Bidens pilosa var. radiata (Bpr) aqueous extracts against the root-knot nematode Meloidogyne incognita. Although the effects of Bpr extracts on nematode populations were ambiguous, knot or gall formation on roots was clearly suppressed by soil drench or seed dip treatments. Tomato plant growth was reduced by some seed dip treatments, but there was no growth or germination inhibition attributable to Bpr extracts among tested crop species in the Leguminaceae, Solanaceae or Cucurbitaceae. Thus, the possibility of nematode control by Bpr soil drench or seed dip treatments was suggested.

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Abstracts of papers presented at the 16th annual meeting of the Japanese Nematological Society in Tsukuba, September 17-19, 2008

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