The seeds of success: release from fungal attack on seeds may influence the invasiveness of alien Impatiens

Kamil Najberek,Pawel Olejniczak,Wojciech Pusz,Wojciech Solarz

doi:10.1007/s11258-018-0872-9

Abstract

Although closely related, Impatiens glandulifera and Impatiens balfourii differ in their invasiveness in Europe; only the former is highly invasive there. Following the assumptions of the enemy release hypothesis (ERH), we tested whether these differences may be explained by the levels of seed infestation by pathogenic fungi. Using seeds collected along the Swiss-Italian border, we recorded four true pathogens of seeds: Fusarium culmorum, F. oxysporum, F. sporotrichoides, and Giberella avenacea. In Italy the seeds of I. balfourii were infected by fungal pathogens more often than those of I. glandulifera, while in Switzerland both species were under the same level of pressure. However, the overall differences in pathogen abundance were consistent with the ERH: seeds of the more invasive species were attacked less. This could be a result of differences between the communities of fungal pathogens attacking the seeds of both species in each country. The number of colonies of secondary pathogens (Cladosporium cladosporioides, Alternaria alternata) correlated negatively with the number of colonies of true pathogens; we suggest that the secondary pathogens may have prevented the occurrence of the true pathogens. The reason for the between-country differences in the fungal pathogen communities is unclear. A possible explanation is that Italy and Switzerland differ in their road and green-area maintenance work schemes, which may have influenced pathogen pressure on seeds. This study is one of the few that offers results indicating that release from enemies may be crucial to the invasion success of plants as early as the seed stage.

Highlights

Biological invasions are a primary threat to biodiversity (Bellard et al 2016; Spatz et al 2017) and a significant cause of economic losses (Vilaet al. 2010; Pimentel 2011)
Pusz Department of Plant Protection, Wroclaw University of Environmental and Life Sciences, Plac Grunwaldzki 24A, 53-363 Wrocław, Poland pathogens (Cladosporium cladosporioides, Alternaria alternata) correlated negatively with the number of colonies of true pathogens; we suggest that the secondary pathogens may have prevented the occurrence of the true pathogens
Since our study focused on assessing the potential negative impact of enemies on seeds of both Impatiens species, we classified the recorded fungal species as true pathogens or secondary pathogens, and used only the former group in the tests

Summary

Introduction

Biological invasions are a primary threat to biodiversity (Bellard et al 2016; Spatz et al 2017) and a significant cause of economic losses (Vilaet al. 2010; Pimentel 2011). Despite the large number of studies of alien Impatiens species (e.g., Kollmann and Banuelos 2004; Adamowski 2008; Janssens et al 2009; Ugoletti et al 2011; Tanner et al 2015; Jacquemart et al 2015; Elst et al 2016), large questions remain, related to the great differences in invasiveness levels between closely related representatives of this genus introduced to the same region. Two such species are I. glandulifera and I. balfourii. Both show high attractiveness to pollinators, self-compatibility, no effect of inbreeding depression (Jacquemart et al 2015), high reproductive capacity (Ugoletti et al 2011; Jacquemart et al 2015), allelopathic potential (Vrchotovaet al. 2011), and antimicrobial and antioxidant properties (Szewczyk et al 2016)

Methods

Results

Discussion

Conclusion