Populations of the Beet Cyst Nematode Heterodera schachtii Exhibit Strong Differences in Their Life-History Traits Across Changing Thermal Conditions.

Sylvain Fournet,Christophe Piriou,Eric Grenier,Josselin Montarry,Lucile Pellan,Catherine Porte

doi:10.3389/fmicb.2018.02801

Abstract

It is widely accepted that climate has an essential influence on the distribution of species and that temperature is the major abiotic factor that affects their life-history traits. Species with very restricted active dispersal abilities and a wide geographical distribution are thus expected to encompass distinct populations adapted to contrasted local conditions. The beet cyst nematode Heterodera schachtii is a good biological model to study temperature adaptation in populations collected from different environments. Here, we tested the effect of temperature on H. schachtii life-history traits using seven field populations from Morocco, Spain, France, Germany, Austria, Poland and Ukraine. We tested hatching and multiplication rates of each population at different temperatures, as well as hatching rates of each population after storage at different temperatures – simulating survival conditions during the inter-cropping period. Results showed a strong temperature effect on the life-history traits explored. Temperature impact on hatching (at different temperatures and after storage at different temperatures) depended on the origin of populations, separating southern from northern ones. Surprisingly, low temperatures influenced hatching less in southern populations. However, for these populations, a storage period at low temperatures strongly reduce subsequent hatching. Conversely, nematode multiplication was not differentially affected by temperatures, as favorable conditions for the host are also favorable for the parasite. Finally, a significant correlation between the genetic diversity and the level of specialization showed that the less diverse populations were more specialized than the more diverse ones.

Highlights

There is no doubt that climate has a major influence on the natural distribution of species (Pearson and Dawson, 2003) and that temperature is the major abiotic factor that affects species phenology (Scranton and Amarasekare, 2017)
ANOVAs revealed a very strong temperature effect for five H. schachtii populations, Fra, Ger, Aus, Pol, and Ukr (Table 1 and Figure 1), showing that the hatching pattern was very different at 11◦C: larvae emergence was lower at 11◦C than at 17 or 23◦C, in terms of Area Under the Hatching Curve (AUHC) (Figure 1) and in terms of cumulative hatching at the end of the experiment (Supplementary Figure S2)
The hatching and development of the beet cyst nematode H. schachtii have been already studied (e.g., Griffin, 1988), far less is known about the survival abilities of this species under different climate conditions that can be encountered during the inter-cropping season

Summary

Introduction

There is no doubt that climate has a major influence on the natural distribution of species (Pearson and Dawson, 2003) and that temperature is the major abiotic factor that affects species phenology (Scranton and Amarasekare, 2017). Plant pathogens, being often distributed across a wide range of climates, are good biological models to study the temperature adaptation of populations from different environments. Patterns of local adaptation to temperature have been highlighted in natural (Laine, 2008) and agricultural host-pathogen systems (Zhan and McDonald, 2011; Mboup et al, 2012; Mariette et al, 2016). The life cycle of many plant pathogens can be split into two alternating phases: the epidemic period, onto or into the host, and the inter-epidemic period, often outside the host. Temperature regimes are likely to differ across locations much more during the inter-epidemic periods than during the epidemic periods, because optimal temperatures for host growth is quite similar whatever the geographical locality

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