Are endophytes an important link between airborne spores and allergen exposure?

Abstract

Grasses represent one of the Earth’s most common plant groups, and natural and cultivated habitats dominated by grasses cover about 40% of the land surface. In turn, each grass species hosts multiple fungal species which can behave as endophytes. An analysis of the endophytic taxa identified in surveys conducted in 14 grass species showed that some of the most frequent taxa on each grass were also present across several host grasses. These taxa were Alternaria, Epicoccum, Cladosporium, Fusarium, and a few others. A similar analysis of airborne fungi surveyed at 41 different locations throughout the world showed that some of the most geographically widespread, and most locally frequent airborne fungi belonged to the same genera that are dominant endophytes in grasses (i.e. Cladosporium, Alternaria, Fusarium, etc.). Therefore, airborne spores of genera that are ubiquitous in grasses are common worldwide and attain high atmospheric concentrations. In addition, spores of the above mentioned fungi are also important respiratory allergens. Direct observation indicates that saprobic colonization and sporulation of non-systemic grass endophytes could become unrestrained when their host plant tissue dies. Subsequently, when appropriate environmental conditions favour sporulation on grass host surfaces, the natural cycle for airborne conidia initiates, and large numbers of these conidia disperse as inoculum for new endophytic infections. Therefore, the cycle of endophytism may be an important link between climate, plant biology and public health.