| The second-stage juvenile (J2) is the only stage for soybean cyst nematode (SCN) to infect soybean root, and its population is directly related with the incidence of the disease it incites. Parasitic ftxngi and bacteria on J2 may be important factors in suppressing SCN and have potential as biocontrol agents of the nematode. One hundred and forty-six rhizospheric soil samples were taken from soybean fields distributed in 61 cities/counties of 11 provinces in China. SCN J2s natively existed (direct method) or after two weeks of addition of 3,000 J2 (baiting method) in 100 g soil were extracted and examined for fungal and bacterial parasitism. The high percentage of J2 parasitized by Hirsutella minnesotensis , H rhossiliensis and Pasteuria sp. were frequently encountered. Combining data from the tests of two methods, parasitism of J2s by H minnesotensis was observed in soil from 20.5% of fields and by H rhossiliensis in soil from 1.4% of fields. Parasitism of J2s by Pasteuria sp. was observed in soil from 26.0% of fields. Species of Aureobasidium, Acremonium, Paecilomyces, Phoma, Arthrobotrys, Trichoderma, Chaetomium and Monilia were also isolated from seven, four, three, three, two, one, one, one samples respectively Hirsute ha spp. were mainly detected in Heilongjiang soils from 19.2% of asseyed fields and occasionaly detected in Shaanxi, Henan and Liaoning. Pasteuria sp. was mainly observed in Huanghuai River Valley, where in the soil from 10.2% in Anhui, 6.8% in Henan, 3.4% in Jiangsu and 2.7% in Shandong, and occasionaly in Heilongjiang, Jilin, Liaoning and Beijing. The high percentage of J2s parasitized by species of Hirsute/la and Pasteuria over 50% up to 100% was observed in soil from a few fields. Comparison of two detection methods, Pasteuria sp. was observed in soil from 21.9% of fields by the baiting methods and from 11.6% of fields by direct method. Hirsute/la spp. were detected in soil from 16.4% of fields by both direct and baiting methods. It was indicated that the baiting method was more effective for detecting Pasteuria sp. but not for detecting Hirsute/la spp. on SCN J2s. Sequencing of 5.85 rDNA between ITS 1 and ITS4 of 1 isolate belonging to H. thompsii and 6 isolates belonging to Hrhossiliensis demonstrated that H. thompsii and H.rhossiliensis were significantly distinguished at molecular level, as well as morphologic taxonomy. Different isolates of H.rhossiliensis from Heterodera glycines J2 were more similar in systematical evolution than those from different host ncmatodes. There was a week relationship between SCN population density and parasitism of the species of Hirsute/la or Pasteuria on J2s but not different significantly. The high parasitism of Hirsute/la spp. were more frequently encountered in sandy loam, alkaline soils with low organic matter content. The relationship between Pasteuria sp. and soil elements was not different significantly. Heterodera glycines, Meloidogyne incognita, Bursaphelenchus xylophilus, Panagrellus redivivus, Steinonema featie, S. capocapsae and Heterorhabdus bacter:phora were selected for the host range test of H minnesotanensis 136, Hrhossiliensis ATCC46487 and Pasteuria sp.. ATCC 46487 infected all nematodes tested, while isolate 136 infected most of the nematodes except M incognita and an isolate of S. fetia. The infection percentage of J2s by ATCC 46487 was higher than that by isolate 136. fsteuria sp. attached only on SCN J2 with mean of 6 spor... |
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