Life history traits and trade‐offs between two species of the ascochyta blight disease complex of pea

Abstract

Plant disease complexes are a playground to investigate coinfections in natural or cultivated systems. Pathogens of such complexes may affect each other through direct and/or indirect interactions and lead to changes in virulence or aggressiveness, offspring production, and transmission. As coinfections by sympatric host‐pathogens can strongly influence pathogen dynamics and their evolutionary trajectories, new insights into the mechanisms of their coexistence is thus of critical importance. In order to characterize differences in ecological niches liable to explain species coexistence on the same host, the inter‐ and intraspecific diversity of the life history traits in natural collections of the two main pathogens (Peyronellaea (formerly Didymella) pinodes [Dp] and Phoma medicaginis var. pinodella [Pmp]) of the ascochyta blight disease complex of pea was evaluated under controlled conditions. Dp strains developed 1.3 times faster and produced longer, mainly bicellular spores and in lower amounts (3.7 times less) than Pmp strains. Pmp strains were separated into two groups, one producing more pycnidiospores, mainly bicellular, with less resources, and the other with mainly unicellular ones. These three groups can be interpreted as three distinct life history strategies: pioneer colonizer (Dp), scavenger (large‐spored Pmp), and intermediate (small‐spored Pmp), allowing differentiation in access to and use of resources. While this experimental work provides new insight into coexistence of two species of the ascochyta blight disease complex of pea, it also raises the question of the benefit of having two distinct life history strategies for one species (Pmp).

Competition and facilitation among fungal plant parasites affect their life‐history traits

“…Pairwise comparisons confirmed the absence of significant differences between Pmp strains, which share the same ‘scavenger' strategy (Dutt et al 2020), for the four LHTs assessed. These LHTs differed between Dp 11 (‘pioneer coloniser') and Dp 13 (‘opportunist') (Fig.…”

“…Strains were single‐spored, and maintained on malt agar slants stored in the dark at 4°C. They were chosen according to their life history trait values (incubation and latent periods, expansion of the necrotic lesion, pycnidiospore production, pycnidiospore length and bicellular rate) measured under single‐infection experiments (Dutt et al 2020). Dp 11 was chosen as a good representative of the ‘pioneer coloniser' strategy, Pmp 10 and Pmp 17 have a ‘scavenger' strategy, while Dp 13 represents the ‘opportunist' strategy.…”

“…For each modality, after 6 days – i.e. when necrotic lesions were well developed, stipules were randomly assigned to one of two equal groups: one batch remained incubated under the same conditions to promote lesion growth, while the other batch was incubated at 20°C in the dark to promote pycnidia formation and pycnidiospore production (Dutt et al 2020).…”

“…The third strategy, shared by some P. medaciginis var. pinodella strains and few P. pinodes strains was 'opportunism', characterised by LHTs intermediate between those observed in the other two strategies (Dutt et al 2020). Moreover, Le May et al (2009) observed variations in total disease development and number of pycnidia produced by the complex under different competitive scenarios, but did not relate these to individual alterations in LHT for each competing partner.…”

“…From an ecological point of view, these differences may thus be explained by discrepancies in the life histories of the pathogen species and/or genotypes involved. Empirical studies suggest that life history traits (LHTs) may considerably differ under multi‐infections compared to single infections (de Roode et al 2005, López‐Villavicencio et al 2007, Alizon et al 2013, Susi et al 2015b, Tollenaere et al 2016, Laine and Mäkinen 2018, Dutt et al 2020). For example, a reduction in disease severity was observed in wheat plants co‐infected with three Mycosphaerella graminicola genotypes compared to single infection (Schürch and Roy 2004).…”