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.

Summary A new species of cyst-forming nematode, Cactodera solani n. sp., from Mexico is described. The new species was found in a glasshouse in Mexico City parasitising tomato and common lambsquarter. This cyst nematode has light brown to almost black cysts, presents a small vulval cone with circumfenestra and morphologically it most resembles C. milleri. Cactodera solani n. sp. can be differentiated from C. milleri by having smaller cysts that are 417 (291-581) × 324 (204-505) vs 632 (515-730) × 506 (419-598) μm in size and a longer stylet in the second-stage juveniles of 25 (24-27) vs 22 (21-23) μm. Phylogenetic relationships within populations and species of Cactodera are given based on the analysis of the ITS rRNA and the partial COI gene sequences. The ITS rRNA and COI gene sequences clearly differentiated C. solani n. sp. from other Cactodera species. This new cyst-forming nematode has several generations per year and its life cycle can be completed in 49 days on tomato and in 40 days on common lambsquarter at 20-25°C.

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El nematodo del quiste de la zanahoria <em>Heterodera carotae</em> es un patógeno importante en <em>Daucus carota</em>. Para que las medidas de control sean efectivas, el conocimiento de la dinámica poblacional del nematodo a través del tiempo es indispensable. El presente trabajo, evaluó la dinámica poblacional de <em>H. carotae</em> en cultivo de zanahoria, durante 10 meses bajo condiciones de invernadero. En junio del 2017, se colocaron en invernadero 90 macetas (3 L volumen): 60 fueron llenadas con suelo naturalmente infestado con el nematodo (1200 J2/maceta) y las 30 restantes se utilizaron como controles (sin nematodos). En cada maceta, se sembraron 10 semillas de zanahoria. Después de la germinación, las macetas fueron muestreadas destructivamente cada 15 y 30 días (n=3). Las raíces de cada maceta fueron pesadas y posteriormente teñidas. Los quistes y J2 se extrajeron del suelo. Las poblaciones de J2 tanto en suelo como raíz, se comportaron de manera similar. En suelo, se observaron tres picos de J2 a los 105, 150 y 195 días con 735, 882 y 967 J2/200 cm3 de suelo respectivamente. Se calculó un factor de reproducción de 1.6 y se observaron cinco generaciones del nematodo. <em>H. carotae</em> causó una pérdida promedio en rendimiento de 70.8% durante el experimento. Los resultados pueden ser usados para desarrollar herramientas en la toma de decisiones para optimizar el momento de implementación de medidas de manejo.