This association is referred to as symbiotic, which means both the plant and the fungus benefit from the relationship. There are several types of mycorrhizal fungi. Mycorrhizal fungi have been colonizing the root systems of plants essentially ever since plants have grown on land. The fungus extends from the root like tiny pipes into the soil or potting medium, greatly enhancing the absorptive surface area of root systems. Scientists are now studying the effects of reintroducing this beneficial soil organism to greenhouse cropping situations.
Reports range from lukewarm to fantastic.
The most consistent and dramatic improvement in host plant growth results from the ability of the fungus to increase phosphorus uptake. This effect is most conspicuous in situations where the soil phosphorus level is low enough to limit growth. Inoculated unrooted cuttings of chrysanthemum, fuchsia and benjamin fig produced more roots that noninoculated cuttings. Inoculation of poinsettia cuttings in the mist bed increased cutting survival, leaf retention and subsequent plant growth. In another study, mycorrhizal fungi slightly reduced the incidence of Pythium root rot in poinsettia.