Protecting Cotton Seedlings From Fungal Attack

When planting the Sure-Grow 747 cotton variety last year, Agricultural Research Service plant pathologist Charles R. Howell was confident that his seedlings would grow just fine under ideal planting conditions. Much to his surprise, his cotton seedlings did not emerge.

The culprit? A damping-off disease caused by Rhyzopus oryzae, a close relative of common bread mold. It’s a disease few growers know about, even though it can strike during a typical growing season. In most cases, the disease causes plants to perish before they rise above ground. The few plants that emerge do not live long because their roots rot.

Howell, based at the ARS Cotton Pathology Research Unit at College Station, Texas, doubts that many farmers realize when this particular problem is happening. They just chalk it up to ordinary cotton seedling disease.

To make matters worse, typical seed treatment fungicides aren’t effective against R. oryzae. For example, there is another more common pre-emergence damping-off disease, caused by the mold Pythium ultimum, that also can be fatal to cotton seedlings germinating under very damp soil conditions. But the seed treatment fungicide normally used to control P. ultimum has no effect on R. oryzae.

To solve this problem, Howell has devised a biological control treatment using the fungus Trichoderma virens. It is grown in liquid cultures, then the solids are dried and ground up. When applied in granular form, this agent controls both P. ultimum and R. oryzae on cotton seed by preventing germination of these molds.

Howell has been working on this project since 2000 and now is talking to crop protection product companies to see if they are interested in commercializing his new product.

According to National Cotton Council data, nearly 2.5 percent of the estimated loss in U.S. cotton bales in 2001 was due to seedling diseases, at a cost of approximately $170 million. It is unknown how much of this may be attributed to R. oryzae.

ARS is the U.S. Department of Agriculture's primary scientific research agency.