A diagnostic gap to fill: Development of molecular tools to distinguish the plant-parasitic nematode species Heterodera carotae and Heterodera cruciferae

The carrot-parasitic nematode, Heterodera carotae, is an important pest causing qualitative and quantitative production losses across several countries worldwide and must be carefully identified and monitored. Indeed, in culture crops, Heterodera carotae and Heterodera cruciferae, two genetically closely related species from the Goettingiana group, can be found in mixture and are virtually morphologically non-recognizable. However, only H. carotae is able to develop on carrot. To monitor carrot production and set up suitable H. carotae control plans, simple and reliable diagnostic methods to detect and identify these two species are needed. In this study, we developed and successfully tested two real-time PCR protocols (SYBR Green singleplex and TaqMan multiplex real-time PCRs) against both sister species: H. carotae and H. cruciferae. Using two specific sets of primers targeting the two species, which were designed from sequences containing microsatellite loci, we managed, whatever the methods, to distinguish the two species. Moreover, we showed a higher specificity using the TaqMan assays (test on cysts) but a better sensitivity (tests on J2 juvenile larvae) with the SYBR Green assays. In this study, we thus proposed two useful and reliable diagnostic tools to enable farmers and scientists to rapidly detect two plant-parasitic nematodes and supervise agricultural management.