The use of Trichoderma spp. to reduce seedling disease severity in cotton

Seedling disease complex of cotton caused by pathogens including Pythium spp., R. solani, T. basicola and Fusarium spp. is important throughout the U.S. cotton belt. The use of fungicides to control seedling disease is expensive, has negative effects to the environment, and is not always successful, particularly when weather conditions favor disease development. Biological control is an alternative for controlling seedling disease. In this study, several cold-tolerant strains of Trichoderma spp. were tested for their efficacy to control the disease.

Trichoderma applied in wheat bran-peat moss preparation was added to raw soil at a concentration of 10⁶ colony forming units per gram of soil and the soil was then placed in plastic pots. After 1 week of incubation, 6 Stoneville 213 cotton seeds were planted per pot. Data on plant height and disease severity were taken 8 and 18 days after planting, respectively. Potential pathogens of seedling disease were isolated from diseased hypocotyls.

Forty isolates comprising 4 species of Trichoderma were tested in a screening procedure. Eight of these plus a new T-8 isolate were retested for further study. Significant reductions in disease severity were obtained with isolates of T. viride. T. harzianum, T. koningii. and T. pseudokoningii. In the initial testing, a few isolates enhanced plant height. However, when retested, none of the isolates increased plant height significantly. Pathogens isolated from diseased hypocotyls were Pythium spp., R. solani and Fusarium spp. Pythium and R. solani were isolated more frequently from severely diseased hypocotyls. Fusarium was isolated mostly from hypocotyls that were less severely diseased. Evidence was obtained that isolates of Trichoderma that significantly reduced disease severity were equally effective for controlling seedling disease caused by R. solani and by Pythium spp.