Nematodes attack cereal crops resulting in significant yield losses, estimated at 10%. The plant parasitic nematodes of the genus Heterodera attack cereals, particularly wheat, causing costly financial losses due to impact on yield. The soil borne pathogens program at the International Maize and Wheat Improvement Center (CIMMYT) in Turkey has focused on screening wheat germplasm to identify sources of Heterodera resistant varieties for almost 20 years. The aim of this current study was to validate the finding that resistant lines demonstrate resistant reactions under controlled conditions and to test whether they present tolerant reactions when challenged with cyst nematodes under two different locations in field conditions. The results of this study, including the check lines, indicated that 27 and 28 lines maintained their reactions to H. filipjevi in Eskisehir and Yozgat field, respectively, and 23 lines were the same in both locations. In terms of tolerance, 3 and 13 lines proven to be tolerant and moderately tolerant to H. filipjevi in Yozgat field. In Eskisehir field, 13 and 14 lines were tolerant and moderately tolerant. In both locations, L7 showed tolerance reaction, although it was susceptible. The majority of the resistant germplasm (60%, 14 lines) of screened lines from the Turkey CIMMYT–ICARDA (TCI) nursery were found to be resistant to both H. filipjevi populations including L1, L3, L6, L15, L21, L26, and L34, whereas 17% (four lines) from the USA had the same reaction. L32 showed a high level of resistance and tolerance in both locations and could prove to be promising lines in the breeding programs. The International Winter Wheat Improvement Program (IWWIP) formerly used these resistant lines in the crossing block and subsequently distributed them to more than 150 international collaborators. Regression analysis revealed a negative correlation between yield and RF of H. filipjevi in both nematode populations, which describes the negative impact of this pest on winter wheat. The results of this study are very important for breeding programs especially for the IWWIP, a joint program between the Turkish Ministry of Agriculture and Forestry, CIMMYT, and the International Centre for Agricultural Research in the Dry Areas (ICARDA).
