The mutualistic relationships grasses have with fungal endophytes is quite an exciting story. Throughout history, all organisms have evolved to counter limiting factors in order to maximize their productivity and fitness, including grasses. The two main factors that limit the fitness of grasses are herbivores that remove the important photosynthetic tissue and stressful environmental conditions such as low soil moisture and high temperature. A strategy that grasses have adopted to battle these limiting conditions is by forming mutualistic relationships with fungi. As strange as it may sound, there are indeed very tiny, tiny fungi that reside within the bodies of grasses! Now that’s something to think about everytime you see some inconspicuous grass growing on the sidewalk. These fungi are known as endophytes, which is a fancy name for fungi that live inside of host plants. Endophytes happily reside within the intercellular spaces of host plants from where they absorb nutrients. There is a metabolic cost associated with the grasses hosting these fungi guests inside their bodies and of course the grasses do not undertake this costly task for free, or they would have died off and gone extinct! The grasses receive a number of benefits from the fungal endophytes such as the production of toxins to deter herbivores, tolerance towards drought conditions, promoting seed germination and seedling growth, increasing biomass, and defense against pathogens. While these fungal endophytes are a blessing for the grasses, the same cannot be said for the animals that feed on the grasses. The toxins that are produced can severely reduce the fitness of herbivory animals such as cows. The toxins can cause symptoms such as fescue foot, fat necrosis and ailments of fescue toxicosis. But here’s when another twist comes into this story. Just as the grasses evolved to have the endophytes to counter the herbivores, some herbivores evolved to counter the fungi in the grasses. The saliva of some herbivores can actually inhibit the growth of the endophytes and its release of the toxins! These complex and deep interactions between grasses and fungal endophytes and herbivores tells a very interesting ecological story about how they have evolved to accommodate each other and survive as best they can.
By Fabbiha Bushra
Applied Plant Ecology Winter 2020 