Aphids increase leaf fungal endophyte diversity and abundance across a plant community regardless of viral infection status and plant nutrition

Abstract

Barley/cereal yellow dwarf viruses (B/CYDVs) are an important group of aphid-vectored viruses that infect grasses worldwide. The virus is transmitted from plant to plant when aphids feed on infected plants and then disperse and feed on uninfected hosts. In this process, aphids likely transfer bacterial and fungal endophytes from the plant microbiome among plants, however, this has not been directly tested. Fungal endophytes provide host plants with protection from herbivores and protect plants against abiotic stressors like drought and nutrient stress. Plant nutrient content shapes aphid feeding preference, the effect of viral infections on plants and increases aphid abundance. Previous work conducted within the lab showed that viral infection in the aphids changed their feeding behaviors. Infected aphids had higher dispersal from host plants and had increased preference for uninfected plants. Thus, we hypothesized that aphids would move fungal endophytes among plants within a neighborhood, however, fertilization and aphids with the virus would increase movement of endophytes among plants.

To explore these hypotheses, we constructed plant communities by placing 100 barley plants within a 10 x 10 grid which were fully enclosed within a sealed enclosure to create replicate plant communities. We added aphids (C/BYDV infected, uninfected, or no aphids) to the center plants within each of the enclosures. Half of the plant communities were randomly selected to receive a fertilization treatment (0.2% or 10% of half-strength Hoagland’s solution). Over the next four months, we randomly harvested plants from each ring of the 10 x 10 grid bi-weekly. We collected ~0.5g of plant leaf tissue, and plated ground leaf tissue on malt extract agar (MEA) petri plate to isolate fungal endophytes from leaf tissue. After 1 week of growth, we identified and enumerated all fungal taxa growing on the plates.

Overall, we found that the presence of aphid vectors increase the diversity (F = 73.86, p = 0.0001), abundance (F = 6.512, p = 0.0028) of fungal endophyte communities, however we found that viral status (Turkey’s diff = -0.502, p = 0.144), plant nutrient status (diversity: F1,59 = 1.91, p = 0.173, abundance: F1,59 = 1.49, p = 0.227), and location (diversity: F3,59 = 1.09, p = 0.361, abundance: F3,59 = 0.626, p = 0.601) of the plants within our plant community had no effect on endophyte diversity or abundance. We performed a PERMANOVA analysis to determine how aphid presence, viral status, fertilization, and location in the plant community shaped endophyte community composition using both abundance-weighted Bray-Curtis distance and presence/absence-weighted Jaccard’s distance. We found that the presence of aphids (BC: r2 = 0.202, p = 0.01) and fertilizer addition (BC: r2 = 0.020, p = 0.05) as well as their interaction (BC: r2 = 0.023, p = 0.01) weakly but significantly altered fungal community composition with both Bray-Curtis and Jaccard’s distance. Our results demonstrate that aphids alter the diversity, abundance, and which fungal taxa are present within barley leaves, while plant nutrient content changes what taxa are in barley leaves without altering the overall diversity or abundance of fungal taxa.