Viability of Neotyphodium endophytic fungus and endophyte-infected and noninfected Lolium multiflorum seeds

Abstract

Neotyphodium endophyte fungi are vertically transmitted symbionts of cool-season grasses. The seed phase of the grass’ life cycle appears to be critical for the persistence of the fungus. Endophyte viability decreases faster than seed viability, but little is known of the effects of this endophyte on seed viability. The endophyte could affect seed viability through changes in water content. Here, we assessed the effects of the endophyte on seed viability, the differential survival of endophyte and seed, and the effects of infection on seed water content. Viability of endophyte-infected and noninfected seeds and endophyte were evaluated over a period of 729 d under 12 controlled environmental conditions. Seed viability was reduced by the infection at high temperature and high relative humidity, but not under other conditions. Moreover, endophyte viability decreased faster than seed viability only under high humidity or high temperature. Seed water content was not affected by endophyte presence. The proportion of viable infected seeds was mainly affected by the loss in endophyte viability and secondly by the differential survival of infected and noninfected seeds. Knowledge on the relative importance of these processes is critical to understand the factors affecting the efficiency of endophyte vertical transmission and the frequency of endophyte-infected plants.

Ontogenetic and trans‐generational dynamics of a vertically transmitted fungal symbiont in an annual host plant in ozone‐polluted settings

“…In addition, endophyte-colonized seeds can germinate and produce endophyte-free seedlings due to a loss of fungal viability (Gundel, Martínez-Ghersa, Batista, & Ghersa, 2010;Gundel, Martínez-Ghersa, Garibaldi, & Ghersa, 2009;Welty, Azevedo, & Cooper, 1987). The vertical transmission process can be disrupted at certain critical ontogenetic phases (e.g., at plant reproduction) by many environmental factors, either abiotic or biotic (Gundel et al, 2008;Gundel, Rudgers, et al, 2011).…”

Contrasting infection frequencies of Neotyphodium endophyte in naturalized Italian ryegrass populations in Japanese farmlands

“…Of these, the latter factor is considered to be improbable because no studies have reported any advantages of endophyte‐uninfected plants for Italian ryegrass as yet. In contrast, several studies have reported the loss of endophyte for Italian ryegrass (Gundel et al. 2009a,b) as well as other ryegrasses (Canals et al.…”

Phylogenetic analysis suggests joint control of transmission mode in a grass-endophyte symbiosis

“…Using recently developed methods for estimating phylogenetic effects on joint traits of 60 interacting species [13,14], we find phylogenetic patterns that point towards joint control 61 of transmission mode. In particular, we find an effect of host phylogeny conditional on 62 the symbiont's identity.…”

“…When hosts control the transmission mode, vertical transmission should 10 evolve under more restrictive circumstances than when symbionts are in control. We 11 take a phylogenetic approach to determine whether the host, symbiont, or both control 12 transmission mode using the pooid grass-epichloid endophyte symbiosis as a model sys- 13 tem. This study is the first to investigate control of transmission mode evolution in a 14 phylogenetic context.…”

“…We determined control of transmission mode by the phylogenetic effects present in the trans-69 mission mode data. We consider five phylogenetic effects, each inducing a different corre-70 3 lation between host-symbiont pairs [14,13]. The host and symbiont effects indicate host 71 and symbiont control, respectively, and cause related hosts (respectively, symbionts) to have 72 similar probabilities of exhibiting a given transmission mode (Figure 1a-b).…”