5.2.10
POTENTIAL BIOCONTROL FUNGI ISOLATED FROM SOYABEAN CYST NEMATODE EGGS FROM CHINA

SLF MEYER1, R HUETTEL1, X-Z LIU2, R HUMBER3, J JUBA4 and J NITAO1

1USDA ARS, Nematology Laboratory, Beltsville, MD 20705, USA; 2Institute of Biological Control, Chinese Academy of Agricultural Sciences, Beijing 100081, China; 3USDA ARS, Plant Protection Research Unit, Ithaca, NY 14853, USA; 4Fusarium Research Center, Pennsylvania State University, University Park, PA 16802, USA

Background and objectives
Soyabean is indigenous to the area that is now the People's Republic of China, and soyabean cyst nematode (Heterodera glycines) is thought to have evolved with soyabean in that location. The nematode has expanded its range along with soyabean and is now the most economically important pest of this crop worldwide. Since biological control agents also tend to evolve with their hosts, fungi associated with H. glycines eggs were isolated from native nematode populations in China. Isolates were then assayed for activity against nematode populations from the USA. The nematodes used in the assays were H. glycines and Meloidogyne incognita (root-knot nematode); the latter is a pest of soyabean and of other crops as well. The objectives of this study were to identify biocontrol fungi or useful natural products from these fungi, and to initiate development of control agents that could be applied in management programmes for these plant pests.

Materials and methods
Cysts of H. glycines were collected from soyabean-growing regions near Anda City and Beijing. Eggs were placed on agar media, and fungi growing from the eggs were isolated and cultured. Assays were developed for determining activity of fungus exudates against eggs of H. glycines and M. incognita. For these assays, fungi were grown in broth and then removed by filtration. Nematode eggs were placed in the broth in multiple-well tissue culture plates, and the number of hatched larvae was counted 2 weeks later. Controls were water and broth that had not been used as a culture medium.

Results and conclusions
More than 250 fungal isolates representing a minimum of 18 genera and 24 species were isolated from the nematode eggs. Genera isolated included Acremonium, Aspergillus, Chaetomium, Chrysosporium, Cladosporium, Cylindrocarpon, Epicoccum, Fusarium, Idriella, Mortierella, Myrothecium, Paecilomyces, Penicillium, Ramichloridium, Trichoderma, Trichothecium, Verticillium, and a new genus. The most frequently isolated genus was Fusarium (ca 84 isolates), which was obtained from all sites and has frequently been reported in Chinese surveys as a member of the H. glycines-associated community [1, 2]. The other genera were isolated from 1 to 25 times each; the latter was the genus Mortierella, which was isolated from three sites. Sterile isolates were not identified. Activity of isolates tested for antagonism to nematode eggs varied with the nematode; egg hatch of M. incognita was more likely to be reduced than H. glycines egg hatch.

References
1. Liu WZ, Liu Y, Duan YX et al., 1995. Korean Journal of Applied Entomology 34, 83-88.
2. Liu XZ, Ding L, Wu XY, Shen CY, 1992. Mycosystema 5, 117-126.