Vertical transmission of fungal endophytes is widespread in forbs

Abstract

To date, it has been thought that endophytic fungi in forbs infect the leaves of their hosts most commonly by air-borne spores (termed “horizontal transmission”). Here, we show that vertical transmission from mother plant to offspring, via seeds, occurs in six forb species (Centaurea cyanus, C. nigra,Papaver rhoeas,Plantago lanceolata,Rumex acetosa, and Senecio vulgaris), suggesting that this may be a widespread phenomenon. Mature seeds were collected from field-grown plants and endophytes isolated from these, and from subsequent cotyledons and true leaves of seedlings, grown in sterile conditions. Most seeds contain one species of fungus, although the identity of the endophyte differs between plant species. Strong evidence for vertical transmission was found for two endophyte species, Alternaria alternata and Cladosporium sphaerospermum. These fungi were recovered from within seeds, cotyledons, and true leaves, although the plant species they were associated with differed. Vertical transmission appears to be an imperfect process, and germination seems to present a bottleneck for fungal growth. We also found that A. alternata and C. sphaerospermum occur on, and within pollen grains, showing that endophyte transmission can be both within and between plant generations. Fungal growth with the pollen tube is likely to be the way in which endophytes enter the developing seed. The fact that true vertical transmission seems common suggests a more mutualistic association between these fungi and their hosts than has previously been thought, and possession of endophytes by seedling plants could have far-reaching ecological consequences. Seedlings may have different growth rates and be better protected against herbivores and pathogens, dependent on the fungi that were present in the mother plant. This would represent a novel case of trans-generational resistance in plants.

Assembly of seed-associated microbial communities within and across successive plant generations

“…These core OTUs were affiliated to bacterial (e.g. Pantoea agglomerans or Pseudomonas viridiflava) and fungal taxa (Alternaria or Cladosporium) that are frequently associated with seeds of various plant species (Barret et al 2015;Hodgson et al 2014;Links et al 2014;Rezki et al 2016;Truyens et al 2015). Altogether, these results suggest a low heritability of the seed microbiota across plant generations.…”

Fusarium graminearum: pathogen or endophyte of North American grasses?

“…There is evidence that endophytic fungi may exhibit some level of host adaptation, as the same fungal species have been isolated from the same host over time and geographic space. For example, Fusarium avenaceum and F. tricinctum have repeatedly been reported as symptomless colonizers of wild grass species (Inch & Gilbert, 2003;Harrow et al, 2010;Turkington et al, 2011;Postic et al, 2012) and occasionally forbs (Hodgson et al, 2014). Fusarium verticillioides has been reported as both a symptomless endophyte and a pathogen of corn (Bacon & Hinton, 1996).…”

Foliar fungal endophyte communities are structured by environment but not host ecotype in Panicum virgatum (switchgrass)

“…), along with occasional re‐colonization of new tissues from the previous season's buds and petioles (Kaneko and Kaneko ) or colonization of seeds via spores dispersed with pollen grains (Hodgson et al. ).…”