| The greenbug, Schizaphis graminum (Rhodani), is a major arthropod pest of wheat, Trticum aestivum L. em. Thell. The primary objectives of the studies were to identify the inheritance mode and chromosome location of the greenbug biotype I resistance genes Gbz, Gbx1, Gba, Gbb, Gbc and Gbd in wheat lines KSU97-85-3, KS89WGRC4, TA4152L94 TA4152L24, TA4063.1 and TA4064.2, respectively. Additional studies were conducted to identify the molecular markers linked to these genes, to determine their genetic relationships, and to determine the resistance categories in several wheat lines. The results indicate that all the genes evaluated are inherited as single dominant traits, and are located in the 18% distal region of the long arm of wheat chromosome 7D (7DL). A total of 12 microsatellite markers are associated with these greenbug resistance genes. Microsatellite marker Xwmc157 is linked to Gbz with zero distance. Markers Xwmc157 and Xgdm150 flank Gbx1 at 2.7 and 3.3 cM, respectively. Xwmc671 is proximally linked to Gba, Gbb, Gbc and Gbd at 34.3, 5.4, 13.7, 7.9 cM, respectively. Xbarc53 is linked distally to Gba and Gbb at 20.7 and 20.2 cM, respectively. Xgdm150 is distal to Gbc at 17.9 cM, and Xwmc157 is distal to Gbd at 1.9 cM. Gbz, Gbx1, Gba, Gbb, Gbc and Gbd are located in the 18% distal region of wheat chromosome 7DL. The wheat lines Largo, TAM 110, KS89WGRC4 and KSU97-85-3 express antibiosis and tolerance to greenbug biotype K. The results also suggest (1) Gbd is a new greenbug biotype I-resistance gene different from Gbx1 and Gbz, (2) Gba, Gbb, Gbc and Gbd are either allelic or linked, (3) Gbz, Gbx1, Gba, Gbb, Gbc and Gbd are linked but not allelic to Gb3, (4) the 18% distal region of Ae. tauschii chromosome 7D are a source of greenbug resistance genes which can be cloned by using map-based procedures, and (5) same wheat genotypes possess different categories of resistance to different greenbug biotypes. |
