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Helping Beneficial Fungi Work


To determine the effects of compost on mycorrhizae in greenhouse production of nursery crops, plant pathologist Robert Linderman and technician Anne Davis grow plants (marigolds shown here) in a potting mix with various levels of compost. Some plants are inoculated with mycorrhizal fungi and others are not. Compost was added to the larger plant that Linderman is holding (left) while none was added to the smaller plant.

(Photo by Peggy Greb / Courtesy USDA / Agricultural Research Service)  

Certain fertilizers can actually inhibit beneficial, naturally occurring fungi that help plants use water and nutrients while suppressing diseases, according to an Agricultural Research Service scientist studying these beneficial root-dwelling fungi.

ARS plant pathologist Robert Linderman at the Horticultural Crops Research Laboratory in Corvallis, Ore., is studying how these fungi, called mycorrhizae, interact with fertilizers and other soil amendments that have been commonly used in agriculture over the past half century.

Linderman is one of only a few scientists studying how mycorrhizae affect the nutrition and health of nursery crops. He has measured the level of mycorrhizal colonization of roots to see whether various materials added to soil help or inhibit fungal growth. He studied a range of commercial fertilizers and found that organic ones are usually compatible with mycorrhizae, while phosphorus-rich inorganic fertilizers usually inhibit them.

He also looked at peat moss, a popular additive to potting mixes used to grow nursery crops. He found that in some cases it helps mycorrhizal associations, while in others it hinders the fungi. Coir, a coconut fiber that has become a popular potting mix additive, does not inhibit mycorrhizae, but it may reduce growth of some plants.

Linderman is currently studying various types of composts to see what, if any, effect they'll have on the establishment of mycorrhizae. His initial finding is that some composts may suppress the fungi because of high phosphorus levels.

After spending years researching these important fungi, Linderman believes that he will now be able to advise growers as to which potting mix additives will help establish mycorrhizae that can enhance plant growth and health.

Read more about this research in the May 2004 issue of Agricultural Research magazine.

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

Source: USDA / Agricultural Research Service, May 6, 2004

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