Abstract: The current indoor screening methods for biocontrol bacteria tend to ignore the basic role of plants; to overcome this drawback, this paper compares the methods of indoor screening for biocontrol bacteria of dual culture, liquid medium screening and seedling substrate screening, then develops a new device based on the improved seedling substrate screening method. This device was modified of the PP-500 mL tissue culture bottle which resistant to high temperature (135 ℃) and high pressure (0.15 MPa). The columnar space of the tissue culture bottle was divided into 3 zones, there were plant growing zone, plant pathogen culture zone, and the candidate biocontrol strain culture one. Each zone was separated by a 0.45 μm nitrate fiber filter membrane. The plant growing zone was open, but the plant pathogen and the candidate biocontrol strain culture zones were closed with a lid. In this device, root exudates of plant growing in approximation of natural conditions and soil exudates were used as substrates to screen candidate biocontrol bacteria, so the results obtained were more reliable. The antagonistic effect of pathogen and candidate biocontrol bacteria was reflected by the change of cell density in this device, which was easy to detect and the result was definite. The device had the advantages of simple structure, low cost and convenient operation. It can be used for batch screening of candidate biocontrol bacteria against various plant root pathogens, but not suitable for screening of that against pathogens of leaf and stalk.

Key words: pathogenic fungi, biocontrol bacteria, screening, Pseudomonas aeruginosa, antagonism