Nematodes Which Challenge Global Wheat Production

1) Effects of cereal cyst (Heterodera) and rootlesion (Pratylenchus) nematodes on wheat are difficult to identify and control. Symptoms are non-specific and easily confused with stress from nutrient deficiency, drought, or disease. 2) Multiple species of Heterodera and Pratylenchus are capable of damaging wheat. Identification of species is difficult and procedures based on comparative morphology can be unreliable. Identification of species is now assisted by molecular tools. 3) Heterodera species discussed in this chapter reproduce only on hosts within the Poaceae, and individual species are highly heterogeneous for virulence to specific host genotypes. Many pathotypes occur within H. avenae, and the same is anticipated for H. filipjevi and H. latipons. No pathotypic variation within either P. neglectus or P. thornei has been reported on wheat, but both species multiply in a wide range of monocot and dicot hosts. Mixtures of Heterodera species or pathotypes, and Pratylenchus species, may occur within individual fields. 4) Field sanitation is important because these nematodes multiply on many weed species and volunteer cereals. Cereal cyst nematode can be controlled by rotating w\heat with a noncereal, a resistant cultivar, or with weed-free fallow. Root-lesion nematode is best managed by rotating resistant and tolerant wheat cultivars with other poor hosts. 5) Resistance and tolerance are genetically independent, and cultivars resistant or tolerant to one species are not necessarily resistant or tolerant to another species. Root-lesion nematode resistance is quantitative and cereal cyst nematode is controlled by single-gene resistance. Molecular markers have been developed to identify genes and quantitative trait loci for resistance in seedlings. 6) Molecular tests to identify and quantify nematodes in commercial soil testing laboratories will allow more effective surveys of populations. Greater collaboration is needed between research institutions, organizations, and countries.