Enhancing Crop Performance and Overcoming Plant Stress with Trichoderma Strains.

A number of organisms colonize plant roots, including fungi in the genus Trichoderma.  These fungi are endophytic in roots (and in some cases in other plant parts) and function as plant symbionts. Trichoderma strains have been known for 80 years as biocontrol agents of plant pathogenic fungi, but we now know that they have many more useful abilities. As root colonists, they induce localized plant resistance that limits their spread within the roots, and establish chemical communication with the plant. This communication results in reprogramming of plant gene expression and changes plant physiology. In addition to plant disease control, plant yields are generally increased, as is root growth. Resistance to abiotic stresses such as drought also occurs, and photosynthetic and respiratory rates probably are increased. In addition, improved nitrogen use efficiency (NUE) also occurs. In seeds, recovery from physiological stresses (aged seeds, for example) occurs, as does resistance to salt and osmotic stress. Seedlings of Arabidopsis have much greater resistance to light stress in the presence than in the absence of Trichoderma. There probably is a common mechanism by which most of these responses are achieved that will be discussed. T. harzianum strain T22 is widely used in commercial agriculture, including root disease control in greenhouses and, as a seed treatment, seeds planted on about 0.5 million acres of wheat were treated because it reliably increases yields. If current field trials support initial findings, newer strains will provide greater NUE, on wheat alone, application of 1 billion pounds of N fertilizer can be avoided while still increasing yields. The understanding of mechanisms by which these beneficial fungi improve plant performance has undergone major changes since about the year 2000, and this new understanding is expected to dramatically increase the use of these fungi in plant agriculture.