DNA barcoding, phylogeny and phylogeography of the cyst nematode species of the Schachtii group from the genus Heterodera (Tylenchida: Heteroderidae)

Summary Cyst-forming nematodes of the genus Heterodera are highly derived and economically important plant parasites. The Schachtii group of this genus is one of the largest ones with a total of 18 species parasitising dicotyledons. In this study, we provided comprehensive phylogenetic analyses of several hundred COI and ITS rRNA gene sequences of selected species from the Schachtii group, including H. betae , H. cajani , H. ciceri , H. galeopsidis , H. glycines , H. medicaginis , H. mediterranea , H. schachtii , H. sonchophila and H. trifolii , using Bayesian inference, maximum likelihood, and statistical parsimony. One hundred and twenty four new COI , 57 ITS rRNA and eight hsp90 gene sequences from 81 nematode populations collected in 19 countries were obtained in this study. Our study showed that the ITS rRNA gene has limited discrimination power compared to the COI gene. However, our analysis also revealed that partial COI gene sequences were identical for H. trifolii , H. betae and H. galeopsidis . Based on the results of phylogeographical analysis and age estimation of clades with a molecular clock approach, it was hypothesised that the majority of the Schachtii group species originated and diversified in the Mediterranean Basin biodiversity hotspot during the Pleistocene and then dispersed from this region across the world. The Sino-Japanese Floristic Region is likely one of the centres of diversification for the soybean cyst nematode, which showed distinct population structure. The possible role of hybridisation and polyploidisation in the evolution of species of the Schachtii group is discussed.