Fungal endophyte–grass symbioses are rare in the California floristic province and other regions with Mediterranean-influenced climates

Research on agronomic grasses has shown that Class 1 fungal endophytes (Neotyphodium/Epichloë; Clavicipitaceae) can have profound effects on host plant fitness. However, in natural systems, even basic ecological knowledge of most endophyte symbioses is lacking. Here, I describe the distribution and abundance of endophytes across 36 native (or naturalized) grasses in a previously unsurveyed region, the California Floristic Province. Symbiosis was generally low: 8.33 % of species and 18.75 % of genera hosted endophytes. I then compared the proportions of symbiotic species and genera found in California and other Mediterranean regions to the proportions found in non-Mediterranean regions. Surveys of Mediterranean-influenced regions showed significantly lower proportions of species (∼66 % lower) and genera (∼65 % lower) hosting endophyte than surveys of non-Mediterranean regions. This pattern suggests that selection in Mediterranean climates may not favor endophyte symbioses.

► Knowledge of most fungal endophyte-plant symbioses is lacking. ► I described the distribution/abundance of endophytes across 36 California grasses. ► Endophyte symbioses were rare in California. ► I compared these data with surveys of grasses from around the world. ► Symbioses were less common in regions with Mediterranean-influenced climates.