To identify loci linked to nematode resistance genes, a total of 126 of CIMMYT advanced spring wheat lines adapted to semi-arid conditions were screened for resistance to Heterodera avenae, Pratylenchus neglectus, and P. thornei, of which 107 lines were genotyped with 1,310 DArT. Association of DArT markers with nematode response was analyzed using the general linear model. Results showed that 11 markers were associated with resistance to H. avenae (pathotype Ha21), 25 markers with resistance to P. neglectus, and 9 significant markers were identified to be linked with resistance to P. thornei. In this work we confirmed that chromosome 4A (~90–105 cM) can be a source of resistance to P. thornei as has been recently reported. Other significant markers were also identified on chromosomal regions where no resistant genes have been reported for both nematodes species. These novel QTL were mapped to chromosomes 5A, 6A, and 7A for H. avenae; on chromosomes 1A, 1B, 3A, 3B, 6B, 7AS, and 7D for P. neglectus; and on chromosomes 1D, 2A, and 5B for P. thornei and represent potentially new loci linked to resistance that may be useful for selecting parents and deploying resistance into elite germplasm adapted to regions where nematodes are causing problem.

Cereal cyst nematodes (CCNs) can cause significant economic yield losses alone or in combination with other biotic and abiotic factors. The damage caused by these nematodes can be enormous when they occur in a disease complex, particularly in areas subject to water stress. Of the 12 valid CCN species, Heterodera avenae, H. filipjevi, and H. latipons are considered the most economically important in different parts of the world. This paper reviews current approaches to managing CCNs via genetic resistance, biological agents, cultural practices, and chemical strategies. Recent research within the soil borne pathogen program of the International Maize and Wheat Improvement Center has focused on germplasm screening, the potential of this germplasm as sources of resistance, and how to incorporate new sources of resistance into breeding programs. Breeding for resistance is particularly complicated and difficult when different species and pathotypes coexist in nature. A lack of expertise and recognition of CCNs as a factor limiting wheat production potential, combined with inappropriate breeding strategies and slow screening processes limit genetic gains for resistance to CCNs.

Tbe distribution of important plant-parasitic and free-living nematodes in tbe cereal production areas of tbe Central Anatolian Plateau (CAP) of Turkey was investigated witb systematic surveys. Two important plant-parasitic nematode groups were found widely distributed; cereal-cyst nematodes (78.3%) and root-lesion nematodes (42.6%). Cereal cyst nematodes (CCN) were identified as Heterodera filipjevi in 18 provinces. Heterodera latipons was found in only one province. Pratylenchus thornei and P. neglectus were tbe most widely distributed species of root-lesion nematodes. Otber frequently recorded plant-parasitic nematodes belonged to tbe genera Geocenamus (52.4%), Pratylenchoides (35.6%), Helicotyienchus (29.7%) and Paratylenchus (19.2%). Konya on tbe soutbern CAP bad a significantly bigb incidence of P. neglectus as well as free-living nematodes. Tbe incidence of CCN was greatest in areas of sandy soils on tbe CAP, witb densities of up to 95 cysts (100 g soil)"'. Population densities of Geocenamus, Pratylenchus and Pratylenchoides were bigb in some locations. Soil pbysicocbemical properties were investigated for tbeir relationship to nematode distribution. Tbere was a sligbt positive correlation of P. thornei and clay content; conversely, there was a significant negative correlation of P. negiectus witb clay and a positive correlation witb sand. Electrical conductivity (EC) was positively correlated witb P. neglectus. Nematodes in tbe genera Heiicotylenchus, Paratylenchus, Trophurus and Tylenchorhynchus were only recorded at low population densities in tbe sampled area. By contrast, nematodes in tbe genera Aphelenchus, Apheienchoides, Dityienchus, Dorylaimus, Tylenchus and bacterivorous genera bad relatively bigb populations. Total free-living nematodes were positively correlated witb EC and zinc (Zn) concentration. Tbe Zn content of soil was generally at a level deficient for plant growtb.

Plant parasitic nematodes are a major biotic cause of wheat-yield loss in temperate wheat-growing regions. A major strategy to develop resistance to root-lesion nematodes (RLNs) in wheat is to assess and then exploit their natural genetic variation. This study examines RLN (Pratylenchus thornei) resistance in 1 Middle Eastern landrace (AUS4930 7.2) and 1 synthetic hexaploid wheat, CROC_1/AE. SQUARROSA (224)//OPATA (CROC), using F2 and F9 populations generated by crossing AUS4930 7.2 and CROC with the susceptible cultivar Pastor, and inoculating these crosses with P. thornei in greenhouse trials. Wheat microsatellite markers linked to previously identified quantitative trait loci (QTLs) for resistance to P. thornei and P. neglectus were used to screen both populations. In the AUS4930 7.2 x Pastor population, resistance loci on chromosomes 1B, 2B, and 6D were detected. Similarly, in the CROC x Pastor population, 2 resistance loci, located on chromosomes 1B and 3B, were identified. Interestingly, a resistance locus located on chromosome 6D was not detected. More detailed mapping is required in these 2 populations, developed using new RLN resistance sources, to determine whether the QTLs identified on these chromosomes are the same, are allelic, or are linked to different resistance loci from those previously identified, and to determine whether these 2 sources contain other novel resistance loci.