Submitted to: Biocontrol Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/26/2000
Publication Date: N/A
Technical Abstract: The drought and high temperatures in Texas cotton growing areas for the past several years have given rise to a disease phenomenon that can have devastating effects on cotton plants. The disease can also lead to a misinterpretation of the effectiveness of strains of Trichoderma spp. as biocontrol agents of cotton seedling disease. The pathogen is Pythium aphanidermatum. This was discovered after cotton seed controls coated with biocontrol agent carrier (wheat bran + peat moss) were killed in soil that had only been infested with very low levels of the test pathogen, R. solani. The fungus found colonizing the dead seed was P. aphanidermatum. When untreated cotton seed were planted in these soils only a very low percentage of the seed showed symptoms of the disease. However, when the seed were coated with the biocontrol carrier alone, 95-100% of the seedlings failed to emerge. When seed coated with biocontrol agent preparations were planted in this soil, 80-90% of the seedlings emerged an survived. However, when the soil was supplemented with 0.5% wheat bran before planting, very few of the biocontrol agent treated seedlings survived. The perceived biocontrol activity was actually due to a failure of the preparation to induce oospore germination of the pathogen in soil. Other sources of organic material such as cow manure or green manure did not cause this problem. These results indicate that the biocontrol strains we currently use to control other seedling disease organisms may not be effective in controlling P. aphanidermatum. A low level of cotton seedling disease is caused by this pathogen. However, P. aphanidermatum may be building up on more mature cotton plants that are stressed by drought and high temperature conditions.