Cereal Cyst Nematodes: A Complex and Destructive Group of Heterodera Species

Abstract

Small grain cereals have served as the basis for staple foods, beverages, and animal feed for thousands of years. Wheat, barley, oats, rye, triticale, rice, and others are rich in calories, proteins, carbohydrates, vitamins, and minerals. These cereals supply 20% of the calories consumed by people worldwide and are therefore a primary source of energy for humans and play a vital role in global food and nutrition security. Global production of small grains increased linearly from 1960 to 2005, and then began to decline. Further decline in production is projected to continue through 2050 while global demand for these grains is projected to increase by 1% per annum. Currently, wheat, barley, and oat production exceeds consumption in developed countries, while in developing countries the consumption rate is higher than production. An increasing demand for meat and livestock products is likely to compound the demand for cereals in developing countries. Current production levels and trends will not be sufficient to fulfill the projected global demand generated by increased populations. For wheat, global production will need to be increased by 60% to fulfill the estimated demand in 2050. Until recently, global wheat production increased mostly in response to development of improved cultivars and farming practices and technologies. Production is now limited by biotic and abiotic constraints, including diseases, nematodes, insect pests, weeds, and climate. Among these constraints, plant-parasitic nematodes alone are estimated to reduce production of all world crops by 10%. Cereal cyst nematodes (CCNs) are among the most important nematode pests that limit production of small grain cereals. Heavily invaded young plants are stunted and their lower leaves are often chlorotic, forming pale green patches in the field. Mature plants are also stunted, have a reduced number of tillers, and the roots are shallow and have a “bushy-knotted” appearance. CCNs comprise a number of closely-related species and are found in most regions where cereals are produced.

Cereal Root Interactions with Soilborne Pathogens—From Trait to Gene and Back

“…In conclusion, deploying effective genetic resistance to soilborne nematode and necrotrophic fungal pathogens of the small-grain cereals remains a challenge. Genetic resistance is dependent on the genotypes of the host and pathogen, and can be location-dependent, as was noted for nematode resistance [7]. Nevertheless, marker technology and linkage analysis software are screens of adapted or semi-adapted cereal genotypes.…”

“…Resistance to P. neglectus and P. thornei was reported in wheat and barley cultivars in Australia and the Pacific Northwest [7,14,26,28]. Wheat generally sustained more damage than barley, and P. thornei was more frequent, and hence more destructive, than P. neglectus [25,26].…”

“…Phytopathogenic nematodes and fungi produce parasitism or disease-inducing proteins, also called effectors, which are introduced into host cells or tissues, and interact with host proteins to produce the susceptible response (disease condition). Genes encoding toxins, cell-wall-degrading enzymes, ROS detoxifying enzymes, or other proteins that undermine host defense processes are attractive candidate HIGS targets [7,88,89].…”

“…Smith) Sacc., Pratylenchus neglectus (Rensch, 1924) Filijev and Stuurmans Stekhoven, 1941, P. thornei Scher and Allen, 1953, Hereodera avenae Wollenweber, 1924, and Meloidogyne graminicola. These pathogens are problems in the dryland production regions of the Pacific Northwest, USA (PNW), Australia, Europe, China, Southeast Asia, India, and other parts of the world [2][3][4][5][6][7]. Furthermore, a body of knowledge is accumulating about the cellular and molecular interactions between these hosts and pathogens that are helping to elucidate the basis of susceptibility and resistance, e.g., References [8][9][10][11][12][13].…”

DNA barcoding, phylogeny and phylogeography of the cyst nematode species of the Avenae group from the genus Heterodera (Tylenchida: Heteroderidae)

“…ustinovi Kirjanova, 1969. Five species from this group are considered as nematode pests and are collectively known as cereal cyst nematodes (CCN) (Smiley et al, 2017). Four CCN species: the European CCN H. avenae, the Filipjev CCN H. filipjevi, the Sturhan CCN H. sturhani and the Australian CCN H. australis, are major, economically important, nematode pests in cerealgrowing areas, whereas the other six species of the H. avenae complex are found parasitising various grass species of less economic relevance to agriculture.…”