Integrative diagnosis of carrot cyst nematode (Heterodera carotae) using morphology and several molecular markers for an accurate identification

Abstract

Cyst nematodes obtained from commercial carrot fields in Ontario (Canada) and northern and southern Italy were subjected to morphological and molecular examination. Morphology of cyst cone tops, males and second-stage juveniles (J2) indicated the nematode species was the Carrot Cyst Nematode (CaCN), Heterodera carotae. The sequence of the Internal Transcribed Spacer (ITS), D2-D3 region of the 28S gene of ribosomal RNA, cytochrome oxidase I of mitochondrial DNA (coxI), and a heat shock protein gene (hsp90), from single cysts were also examined. Sequences of ITS and D2-D3 placed all the nematodes with Heterodera carotae and other Heterodera spp. belonging to the Goettingiana group in the same clade. The novel nine coxI sequences obtained also clustered in a well-supported phylogenetic clade for H. carotae. Similarly, the six new hsp90 sequences of H. carotae generated in this study were placed in a well-supported clade (PP = 1.00) together with other two sequences of H. carotae from Greece. Restriction Fragment Length Polymorphism (RFLP) of ITS-PCR products gave a restriction pattern for RsaI different than H. carotae but the other 6 restriction patterns were similar as described in former research. A diagnostic conventional PCR method was developed based on a primer set to be specific for H. carotae using coxI sequence. These primers were also used in real time PCR to generate a melt curve specific to H. carotae. Limit of detection for CaCN in conventional PCR reaction was a single J2.