Light Converts Endosymbiotic Fungus to Pathogen, Influencing Seedling Survival and Niche-Space Filling of a Common Tropical Tree, Iriartea deltoidea

Abstract

Pathogens are hypothesized to play an important role in the maintenance of tropical forest plant species richness. Notably, species richness may be promoted by incomplete filling of niche space due interactions of host populations with their pathogens. A potentially important group of pathogens are endophytic fungi, which asymptomatically colonize plants and are diverse and abundant in tropical ecosystems. Endophytes may alter competitive abilities of host individuals and improve host fitness under stress, but may also become pathogenic. Little is known of the impacts of endophytes on niche-space filling of their hosts.Here we evaluate how a widespread fungal endophyte infecting a common tropical palm influences its recruitment and survival in natural ecosystems, and whether this impact is modulated by the abiotic environment, potentially constraining host niche-space filling. Iriartea deltoidea dominates many wet lowland Neotropical forests. Diplodia mutila is a common asymptomatic endophyte in mature plants; however, it causes disease in some seedlings. We investigated the effects of light availability on D. mutila disease expression.We found I. deltoidea seedlings to preferentially occur under shady conditions. Correspondingly, we also found that high light triggers endophyte pathogenicity, while low light favors endosymbiotic development, constraining recruitment of endophyte-infested seedlings to shaded understory by reducing seedling survival in direct light. Pathogenicity of D. mutila under high light is proposed to result from light-induced production of H2O2 by the fungus, triggering hypersensitivity, cell death, and tissue necrosis in the palm. This is the first study to demonstrate that endophytes respond to abiotic factors to influence plant distributions in natural ecosystems; and the first to identify light as a factor influencing where an endophyte is placed on the endosymbiont–pathogen continuum. Our findings show that pathogens can indeed constrain niche-space filling of otherwise successful tropical plant species, providing unoccupied niche space for other species.

Fungal Endosymbionts of Seaweeds

“…There is no information regarding the cost and benefit of endosymbiont association with seaweeds. Some fungal pathogens survive as symptomless endophytes in tissues of terrestrial plants and induce disease under suitable environmental conditions or when the host's defence is weakened (Suryanarayanan and Murali 2006;A'lvarez-Loayza et al 2011). If pathogenic fungi can exist as latent pathogens in seaweeds, they can be harnessed to control undesirable and invasive seaweeds which are detrimental to marine ecosystems (Anderson 2007).…”

Characterization of community structure of culturable endophytic fungi in sweet cherry composite trees and their growth-retarding effect against pathogens

“…Endophyte infection is assumed to remain asymptomatic, although the host-endophyte interrelation is complex and may range from mutualism to antago-Acta Biologica Hungarica 67, 2016 nism depending on environmental conditions [1]. Evidently, fungal symbionts have a pivotal impact on plant survival and fitness and are probably able to induce augmented host tolerance to different kinds of stresses such as drought, salinity, heat shock and abiotic agents [5,33].…”

“…Moreover, endophytes may contribute to the host plant's defence against natural pathogens and may even protect the host from insect herbivores by indirect mechanisms [26]. Empirical evidence demonstrates that reciprocal cooperation between host and fungal symbiont is species-specific and strongly related to the phylogenetic diversity of both partners [1,3,13].…”

Re-classification of the causal agent of white grain disorder on wheat as three separate species of Eutiarosporella

“…Species of Botryosphaeriaceae are widespread across the world, and are observed as both pathogens and endophytes (or potential pathogens) on a wide range of plant hosts (Sakalidis et al 2011a(Sakalidis et al , 2013Alvarez-Loayza et al 2011;Slippers and Wingfield 2007). In Australasia, a selection of these includes conifers , eucalypts (Barber et al 2005;Slippers et al 2004b), mangoes (Sakalidis et al 2011a), grapes (Taylor et al 2005) and baobabs (Sakalidis et al 2011a).…”