Mycorrhiza Reduces Adverse Effects of Dark Septate Endophytes (DSE) on Growth of Conifers

Abstract

Mycorrhizal roots are frequently colonized by fungi of the Phialocephala fortinii s.l. – Acephala applanata species complex (PAC). These ascomycetes are common and widespread colonizers of tree roots. Some PAC strains reduce growth increments of their hosts but are beneficial in protecting roots against pathogens. Nothing is known about the effects of PAC on mycorrhizal fungi and the PAC-mycorrhiza association on plant growth, even though these two fungal groups occur closely together in natural habitats. We expect reduced colonization rates and reduced negative effects of PAC on host plants if roots are co-colonized by an ectomycorrhizal fungus (ECM). Depending on the temperature regime interactions among the partners in this tripartite ECM-PAC-plant system might also change. To test our hypotheses, effects of four PAC genotypes (two pathogenic and two non-pathogenic on the Norway spruce), mycorrhization by Laccaria bicolor (strain S238N) and two temperature regimes (19°C and 25°C) on the biomass of the Douglas-fir (Pseudotsuga menziesii) and Norway spruce (Picea abies) seedlings were studied. Mycorrhization compensated the adverse effects of PAC on the growth of the Norway spruce at both temperatures. The growth of the Douglas-fir was not influenced either by PAC or mycorrhization at 19°C, but at 25°C mycorrhization had a similar protective effect as in the Norway spruce. The compensatory effects probably rely on the reduction of the PAC-colonization density by mycorrhizae. Temperature and the PAC strain only had a differential effect on the biomass of the Norway spruce but not on the Douglas-fir. Higher temperature reduced mycorrhization of both hosts. We conclude that ectomycorrhizae form physical and/or physiological barriers against PAC leading to reduced PAC-colonization of the roots. Additionally, our results indicate that global warming could cause a general decrease of mycorrhization making primary roots more accessible to other symbionts and pathogens.

Influence of season and edaphic factors on endorhizal fungal associations in subtropical plantation forest trees of Northeastern India

“…This is in contrast to the finding where a positive correlation has been reported between DSE colonization and root length with AM fungal hyphae (Lingfei et al, 2005). Experimental studies on ectomycorrhizal-DSE-plant systems have shown a reduction in DSE fungal colonization in response to ectomycorrhization (Reininger and Sieber, 2012) and this effect was speculated to be the result of competition for space and nutrients or direct antagonism between DSE and mycorrhizal fungi. However, this has yet to be examined for AM and DSE fungal interactions.…”

The co-existence between DSE and AMF symbionts affects plant P pools through P mineralization and solubilization processes

“…The dual colonisation of plant roots by DSE and AMF has been recognised since the work of Peyronel (1924). However, reports showing tripartite interactions among DSE, AMF and plants are scarce, with previous authors emphasizing the need for integrating research on mycorrhizal and fungal root endophytes (Scervino et al, 2009;Porras-Alfaro and Bayman, 2011;Reininger and Sieber, 2012). One such study shows that AMF can be influenced by the metabolism of Dreschlera sp., a DSE, with exudates from the latter being found to modulate the mycorrhizal state in the two stages of the life cycle of the symbionts (Scervino et al, 2009).…”

Diversity and antagonistic activity of endophytic fungi from sweet cherry and pepper

“…DSE have little DOI: 10.14267/phd.2015062 host or habitat specificity; they have been reported in association with ≈600 plants including plants that are non-mycorrhizal, from Antarctic, Arctic, alpine, sub-alpine, and temperate zones, as well as from African coastal plains and lowlands, and from some tropical ecosystems (Jumpponen et al 1998). DSE are often found in boreal and temperate forests associated with the fine roots of trees and shrubs, especially of conifers (Reininger & Sieber, 2012). These fungi are not thought to be pathogenic, as they are observed on healthy fine roots, and in this context, may be referred to as endophytes.…”

“…Such a result may imply the ability of this genus to colonize host tissue with no detectable symptom, however these fungi are normally considered as plant DOI: 10.14267/phd.2015062 pathogens. There is a body of evidence that confirms symbiotic life style of Fusarium sp., with plants (Jumpponen et al, 1998); (Kaplan et al, 2013); (Reininger & Sieber, 2012) that altogether they highlight the importance of these fungi in bio-ecosystem and their impact on plant pathophysiology. Some endophytes isolated from cherry rootstocks have formerly been shown to be beneficial to the host.…”