5.2.2
PREPARATION AND APPLICATION OF BIOLOGICAL CONTROL AGENTS TO CONTROL COTTON WILTS OF FUSARIUM AND VERTICILLIUM

PING DONG, QING JI, TAO LONG and GULINUR AHMAT

Institute of Microbiology, Xinji, Urumqi, PR China

Background and objectives
Cotton wilts of Fusarium and Verticillium are very common in Xinjiang and throughout China, greatly affecting the yield and quality of cotton. It is very difficult to control the diseases either by chemical or biological methods. There are many microorganisms antagonistic to Fusarium oxysporium and Verticillium dahliae in the roots and rhizosphere of cotton. Theoretically, these kinds of microorganisms can be used to control the cotton soilborne diseases of Fusarium and Verticillium.

Materials and methods
A number of fungi, bacteria and actinomycetes were isolated from cotton roots and rhizosphere, and were screened in the laboratory and in plot tests. Six isolates were obtained that showed high levels of control of the pathogens and promotion of plant growth. The isolates were fermented, then metabolic products were extracted with acetone and condensed, filtered and dried by vacuum spray. A plot trial was carried out in the main cotton-producing areas of Xinjiang. The treatments included seed mixing with the agents before planting, and spraying during the growing season.

Results and conclusions
The isolates were identified as Trichoderma spp., Bacillus spp. and Streptomyces spp. The agents were prepared in powder and liquid form. The field trial results showed that control by the agents of Fusarium cotton wilt was 73.2% and of Verticillium wilt, 51.6%, and the yields were raised to 28.5 and 15.9%, respectively. It is concluded that these biological control agents can be used to effectively control Fusarium and Verticillium cotton wilts and to promote growth of cotton plants.

References
1. Callow JA, 1997. Botanical Research 26, 1-134.
2. McQuilken MP, Mitchell SJ, Budge SP, 1995. Plant Pathology 44, 883-896.