Endophytic fungal diversity of Fragaria vesca, a crop wild relative of strawberry, along environmental gradients within a small geographical area

Abstract

Background: Fungal endophytes are highly diverse ubiquitous asymptomatic microorganisms, some of which appear to be symbiotic. Depending on abiotic conditions and genotype of the plant, the diversity of endophytes may confer fitness benefits to plant communities.

Methods: We studied a crop wild relative (CWR) of strawberry, along environmental gradients with a view to understand the cultivable root-derived endophytic fungi that can be evaluated for promoting growth and tolerating stress in selected plant groups. The main objectives were to understand whether: (a) suboptimal soil types are drivers for fungal distribution and diversity; (b) high pH and poor nutrient availability lead to fungal-plant associations that help deliver fitness benefits; and (c) novel fungi can be identified for their use in improving plant growth, and alleviate stress in diverse crops.

Results: The study revealed that habitats with high pH and low nutrient availability have higher fungal diversity, with more rare fungi isolated from locations with chalky soil. Plants from location G were the healthiest even though soil from this location was the poorest in nutrients. Study of environmental gradients, especially extreme habitat types, may help understand the root zone fungal diversity of different functional classes. Two small in vitro pilot studies conducted with two isolates showed that endophytic fungi from suboptimal habitats can promote plant growth and fitness benefits in selected plant groups.

Discussion: Targeting native plants and crop wild relatives for research offers opportunities to unearth diverse functional groups of root-derived endophytic fungi that are beneficial for crops.

Keywords: Beneficial fungus; Biomass; Fitness benefit; In vitro; Root; Soil; Stress.

Figure 1. Locations (A–G) from where Fragaria vesca plant and soil samples were collected for the study.

(Map data © 2016 Google).

Figure 2. Abundance of the 12 common (blue bars) and 49 rare (orange bars) OTUs at each location.

(A) Three roots from each of two plants were cultured from each location; with six roots per location, the isolation of the same OTU from all six roots from the same location scored a maximum score of 6 for abundance (fully horizontally extended bar). (B) Distribution of the OTUs in each location after their grouping into families (red bars).

Figure 3. Non-metric multidimensional scaling (NMDS) plot showing diversity of root-derived endophytic fungi among six roots from each of seven locations (A–G) along environmental gradients (levels of Ca, humus, P and pH).

Filled grey circles indicate common endophytes; empty grey circles indicate rare endophytes. The four fitted environmental vectors showed correlations on the ordination plot with significance (Ca, P and pH: p < 0.01; humus: p < 0.05).

Figure 4. Shoot and root measurements of wild strawberry, Fragaria vesca, from seven locations (A–G).

Data represents means for each characteristic from two plants from each location.

Figure 5. Effect of endophytes Humicola sp.-like F2A(13) and Volutella rosea-like G3B(10) on shoot and root weights of rye and common vetch.

(A) Fresh weight (FW) and dry weight (DW) of shoots and roots. (B) DW/FW ratios and root/shoot weight ratios. ¹Mean ± standard errors are shown (n = 5 for each treatment group). ²Statistically significant differences are indicated (ns: not significant; ^∗: significant at 0.01 ≤ p < 0.05; ^∗∗ significant at p < 0.01) as determined by comparison of treatment to control using the Games–Howell test.

Figure 6. Effect of Humicola sp.-like F2A(13) and Volutella rosea-like G3B(10) on radish cultures that have been co-cultured with one of the endophytes for 12 weeks in vitro on sucrose-free medium.

Mean ± standard errors are shown (n = 7 for Humicola sp.-like F2A(13), n = 8 for control and Volutella rosea-like G3B(10)) for (A) number of root branches that were longer than 10 mm, the (B) volume of medium used from a starting volume of 40 ml, and (C) shoot length. Statistically significant differences are indicated (∗∗); all treatments differed from control at p < 0.01 as determined by comparison of treatment to control using the Games–Howell test.