Spatial distribution and basic ecology of Heterodera schachtii and H. betae wild populations developing on sea beet, Beta vulgaris ssp. maritima

Abstract

Most populations of crop pathogens have wild relative populations from which they can originate but for which basic knowledge of their ecological requirements in natura is scarce. However, the study of spatial distribution and ecology of wild pathogen populations may help control them in crops through a better understanding of the environmental factors driving population dynamics.Here, we focused on Heterodera schachtii and H. betae, two cyst nematodes that cause severe damage to sugar beet (Beta vulgaris ssp. vulgaris) crops and can develop on a wild beet relative, the sea beet (B. vulgaris ssp. maritima). We investigated the occurrence of both nematode species in the wild and explored some environmental factors that may influence their geographical distribution. To do so, we sampled the wild host B. v. ssp. maritima along the European Atlantic and North Sea coastlines. Results showed that H. schachtii mainly occurred in the colder environments of northern Europe, whereas H. betae was preferentially distributed in the warm environments of southern Europe. It was previously established that H. betae only recently appeared in The Netherlands, which are in the north of Europe. Thus, our results do not support this hypothesis. Overall, this study accurately documents the geographical occurrence of two nematode crop pest species in the wild and helps identify the main environmental factors affecting their distribution range.

Effect of Temperature on the Hatch of Two German Populations of the Beet Cyst nematodes, Heterodera schachtii and Heterodera betae

“…A recent study on the spatial distribution of both beet cyst nematodes on sea beet, Beta vulgaris spp. maritima reported that H. schachtii mainly occurred in the colder environments of northern Europe, whereas H. betae was preferentially distributed in the warmer environments of southern Europe (Gracianne et al 2014).…”

Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 1. Insights from the estimation of effective population sizes

“…DNA extraction, PCR amplification of ITS sequence, and digestion of PCR products were performed as described in Gracianne et al. ().…”

“…By multiplying the ratio of H. schachtii among the 40 larvae with the number of cysts we sampled, we estimated the number of H. schachtii cysts contained in our samples. DNA extraction, PCR amplification of ITS sequence, and digestion of PCR products were performed as described in Gracianne et al (2014).…”

“…Crop pathogens or parasites can also be found in wild hosts (Barr es et al 2008;Barrett et al 2009;Gracianne et al 2014), particularly because wild hosts are the initial host species before domestication or because parasites can also subsequently shift to other cultivated plants (Stukenbrock and McDonald 2008). Once in a cultivated environment, the geographical distribution, host associations, and disease dynamics of pests are mainly influenced by human activities (Morgan et al 2012;Bousset and Ch evre 2013).…”

Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 2. Separating the relative effects of gene flow and genetic drift

“…Sea beets are common along the European Atlantic and Mediterranean coastlines (De Cauwer, Dufay, Cuguen, & Arnaud, 2010;Hautekèete, Piquot, & Van Dijk, 2002). Wild populations of H. schachtii have been found on wild sea beet populations located along the Atlantic coastline from Spain to Denmark (Gracianne et al, 2014). This wide geographical occurrence provides the opportunity to explore the patterns of gene flow over different spatial scales in the wild.…”