Morphological and molecular diagnostics for plant-parasitic nematodes: working together to get the identification done

OUTLINE Nematodes are considered one of the most difficult organisms to identify due to their microscopic size, morphological similarity, limited number of distinguishable taxonomic characters and overlapping morphometric measurements. However, there are few trained nematode taxonomists remaining, primarily due to retirement without replacement and/or young scientists’ lack of interest in classical taxonomy. Due to the continuing decline in classical taxonomic expertise of many taxa including Nematoda, there is an increasing reliance on developing molecular-based diagnostic protocols to identify pests and pathogens. To improve the resolution and reliability of nematode phylogenetic and diagnostic studies, they should ideally combine morphological with molecular data. However, few of the published studies have compared phylogenetic trees derived from morphological/morphometric characters with those derived from molecular data. Furthermore, nematode sequences deposited in public databases should have an identification based on morphological and morphometrical characters ascertained by a trained taxonomist. Nevertheless, molecular diagnostics do offer new opportunities in Nematology, such as improving the capacity to deal with large numbers of samples or with species mixtures which have previously been impractical. In conclusion, a balanced molecular and morphological taxonomic approach is required as proposed by the integrative taxonomy concept. Classical taxonomy and molecular diagnostics should be considered as complementary.