First report of carrot cyst nematode Heterodera carotae in Mexico: Morphological, molecular characterization and host range study

During 2008 to 2016 in several nematological surveys in the Tepeaca Valley, Puebla, Mexico, carrot cyst nematode, Heterodera carotae was found parasitizing carrots, Daucus carota. The nematode was present in 61% of the sampled fields with high population densities, causing severe carrot yield losses in the Tepeaca Valley. The aim of this work was to study morphology, morphometrics, host range, and molecular characterization of the nematode. The morphological and morphometric characterization was made using light and scanning electron microscopy of the second stage juveniles, females, males and cysts, and the host range study, was performed with nine different plants from five families. The molecular identification was made by sequencing and analysing the ITS rRNA and partial COI genes. It was shown that using presently available molecular tools it is not possible to make an accurate differentiation of H. carotae from H. cruciferae. The host range test allowed to distinguish these species from each other. Our study showed that male stylet length is longer for H. carotae compared with that for H. cruciferae. This is an example of importance of combination of several methods for the correct identification of cyst nematodes. To our knowledge, this is the first report of H. carotae in Mexico.