The Friendly Fungus
by Dr. Robert Black, Consumer Horticultural Specialist

Home gardeners usually associate fungi with leaf spots, stem and root rots, and other dreaded plant diseases. This association is only natural since fungi are responsible for many plant diseases. However, there is a group of friendly fungi called mycorrhizal fungi which enhance plant growth.

Mycorrhizal fungi are found on the roots of most plants in their natural habitats. The associations of mycorrhizal fungi and plant feeder roots are called mycorrhizae. Mycorrhizae are true symbiotic relationships. The fungi effectively increase the surface area of the root system, thus increasing the root system's capacity to absorb nutrients and water. Fungi in turn obtain needed carbohydrates by surrounding and penetrating root cells. The increased absorptive capacity provided by mycorrhizae increases plants drought tolerance and their ability to survive on poor soils. This will become more important as Florida continues to become more urbanized and demand increases on our already dwindling water supply.

Researchers speculate that mycorrhizae may increase root and shoot growth by participating in the manufacture of plant hormones. They also suspect that mycorrhizae may increase plant roots' resistance to soil borne diseases by producing antibiotics or acting as mechanical barriers.

What does all this mean to the nurseryman and most importantly, to you the home gardener? It means that mycorrhizae may enable nurserymen to grow a plant to a salable size faster while at the same time reducing his production costs. These savings could be passed to the home gardener, who should be able to purchase a high quality plant at a very reasonable price. The benefits to the home gardener may continue after the plant is purchased and planted in the landscape. Mycorrhizal plants have a better chance of surviving since they are more efficient in absorbing water and nutrients.

At this point, you may be wondering why you can't find mycorrhizal plants at your local nursery or garden supply dealer. The reason is that many questions about mycorrhizae remain unanswered. Researchers at the Institute of Food and Agricultural Sciences have been experimenting with mycorrhizae from the time a plant is inoculated with the mycorrhizal fungus in the nursery to the time the plant is installed in a landscape. They know that there are many species of mycorrhizal fungi and that some stimulate plant growth better than others for a given plant species. They also know that the relationship between the fungi and plant roots is biological and cultural practices such as fertilizing and applying pesticides can effect this delicate relationship. As you have probably guessed by now, the likelihood of buying plants which have been inoculated with mycorrhizal fungi may be several years down the road. However, the benefits to the nurseryman, consumer and our environment make mycorrhizal plants well worth the wait.