Endophytes are ubiquitous components of plant microbiomes that asymptomatically colonize the internal tissues of plants. Fungal endophytes may affect host plant growth, phytohormone production, and response to environmental stressors such as drought. We isolated a two-species complex of fungal endophytes (LG2) from the fruit of Capsicum annuum pepper plants, and are using morphological and molecular methods to identify these species. In this study, we examined the effects of each of the two endophyte species, and of the endophyte complex, on C. annuum seedling growth, drought tolerance, and drought recovery. Antohi Romanian C. annuum seeds were treated with endophyte spore suspensions and grown under laboratory or greenhouse conditions. Seedlings were exposed to drought conditions, and response to drought was measured as time to initial wilt, full wilt (leaves vertical and curled), and plant mortality. Drought recovery was examined by resuming watering after seedlings reached full wilt. Recovery was measured as the time from full wilt to full leaf recovery. Seedling biomass was measured 2 weeks after full wilt recovery to determine if the endophytes mediate the effects of drought on seedling growth.
The LG2 endophyte complex is composed of two distinct morphotypes: orange (LG2O) and grey (LG2G). The orange morphotype is characterized by ellipsoid to oblong-shaped spores, and septate linear and corkscrew hyphae with appressoria. The grey morphotype is characterized by lemon-shaped spores with large, robust, septate hyphae. We have preliminarily identified LG2O as a member of the genus Colletotrichum, and identification of LG2G is ongoing.
Treatment of C. annuum seeds with the endophyte complex resulted in significantly greater shoot biomass (p<0.001), root biomass (p=0.006), and shoot height (p=0.007). Additionally, LG2 endophyte-complex treated seedlings exposed to a 4 day drought period had significantly less wilting in comparison to control seedlings (p<0.001). When pepper seedlings were treated with only LG2O spores, we observed no significant effects on shoot biomass (p=0.153), root biomass (p=0.85), or shoot height (p=0.11). We are currently examining the effects of LG2G spores on plant biomass and response to drought, and how LG2O and LG2G may interact to affect pepper seedling characteristics. Changing environmental conditions make it important to understand how endophytes affect host plant responses to drought and how this may impact host plant distributions.