Patterns of thermal adaptation in a worldwide plant pathogen: local diversity and plasticity reveal two-tier dynamics

Abstract

 Plant pathogen populations inhabit patchy environments with contrasting, variable thermal conditions. We investigated the diversity of thermal responses in populations sampled over contrasting spatiotemporal scales, to improve our understanding of their dynamics of adaptation to local conditions.  Samples of natural populations of the wheat pathogen Zymoseptoria tritici were collected from sites within the Euro-Mediterranean region subject to a broad range of environmental conditions. We tested for local adaptation, by accounting for the diversity of responses at the individual and population levels on the basis of key thermal performance curve parameters and 'thermotype' (groups of individuals with similar thermal responses) composition. The characterisation of phenotypic responses and genotypic structure revealed: (i) a high degree of individual plasticity and variation in sensitivity to temperature conditions across spatiotemporal scales and populations; (ii) geographic adaptation to local mean temperature conditions, with major alterations due to seasonal patterns over the wheatgrowing season. The seasonal shifts in functional composition suggest that populations are locally structured by selection, contributing to shape adaptation patterns. Further studies combining selection experiments and modelling are required to determine how functional group selection drives population dynamics and adaptive potential in response to thermal heterogeneity.

Differential tolerance of Zymoseptoria tritici to altered optimal moisture conditions during the early stages of wheat infection

“…The Israeli and Irish Z. tritici populations studied here are part of a Euro-Mediterranean set of eight populations included in a broader study on thermal adaptation (Boixel et al , 2019b). General ecological concepts, knowledge and methods have been developed to a greater extent for thermal biology than for moisture biology.…”

“…Two Z. tritici populations were collected on wheat after the stem elongation stage from contrasting Köppen-Geiger Euro-Mediterranean climatic zones: (i) an Irish population (IR) sampled in July 2016 on cultivar JB Diego from a single field at Carlow (52°83’65’’ N - 6°93’41’’ E; Cfb, oceanic climate); (ii) an Israeli population (IS) sampled in March 2017 on cultivar Galil from a single field at Kiryat-Tivon (32°71’62’’ N - 35°12’74’’ E; Csa, hot-summer Mediterranean climate). These two populations, which have already been characterized for thermal adaptation and genotyped for 12 neutral genetic markers (Boixel et al , 2019b), originate from environments with different average air moisture conditions, mainly due to marked differences in annual temperature and rainfall regimes (Figure 1). We randomly selected 24 IR and 24 IS Z. tritici isolates from these populations and checked that they were different multilocus genotypes (Boixel et al ., 2019b).…”

“…Phenotypic differentiation in terms of the intercept, slope and midpoint was compared to between-population neutral genetic differentiation, to determine the potential for local adaptation of moisture responses (P ST - F ST comparisons performed with the ‘ Pstat ’ R package). Neutral genetic variability, and the structure and distribution of diversity between and within the IR and IS populations were characterized in a previous study (Boixel et al , 2019b) based on microsatellite genotyping data acquired for 12 SSRs (ST1, ST2, ST3A, ST3B, ST3C, ST4, ST5, ST6, ST7, ST9, ST10, ST12 neutral microsatellites; Gautier et al , 2014). In parallel, components of phenotypic variation in the response to the four moisture regimes (R0, R1, R2, R3) were extracted by principal component analysis.…”

Differential tolerance of Zymoseptoria tritici to altered optimal moisture conditions during the early stages of wheat infection

“…The copyright holder for this preprint (which this version posted February 8, 2021. ; https://doi.org/10.1101/867572 doi: bioRxiv preprint Two Z. tritici populations were collected on wheat after the stem elongation stage from contrasting Köppen-Geiger Euro-Mediterranean climatic zones: (i) an Irish population (IR) sampled in July 2016 on cultivar JB Diego from a single field at Carlow (52°83'65'' N -6°93'41'' E; Cfb, oceanic climate); (ii) an Israeli population (IS) sampled in March 2017 on cultivar Galil from a single field at Kiryat-Tivon (32°71'62'' N -35°12'74'' E; Csa, hotsummer Mediterranean climate). These two populations, which have already been characterized for thermal adaptation and genotyped for 12 neutral genetic markers (Boixel et al, 2019b), originate from environments with different average air moisture conditions, mainly due to marked differences in annual temperature and rainfall regimes (Figure 1). We randomly selected 24 IR and 24 IS Z. tritici isolates from these populations and checked that they were different multilocus genotypes (Boixel et al, 2019b).…”

“…These two populations, which have already been characterized for thermal adaptation and genotyped for 12 neutral genetic markers (Boixel et al, 2019b), originate from environments with different average air moisture conditions, mainly due to marked differences in annual temperature and rainfall regimes (Figure 1). We randomly selected 24 IR and 24 IS Z. tritici isolates from these populations and checked that they were different multilocus genotypes (Boixel et al, 2019b). These populations were phenotyped in three sequential randomized batches of 16 isolates at a time under controlled conditions in a growth chamber experiment with four treatments (different moisture regimes but identical temperature conditions).…”