Liu Jin-Dong; Chen Xin-Min; He Zhonghu; Wu Ling; Bai Bin; Li Zai-Feng; Xia Xian-Chun
Pyramiding quantitative trait loci (QTLs) is an effective method to improve resistance to powdery mildew, stripe rust, and leaf rust in common wheat. We have developed 21 lines (F6) carrying 2-5 slow mildewing QTLs by crossing slow powdery mildew cultivars Bainong 64 and Lumai 21 possessing four and three slow mildewing QTLs, respectively. These F6 lines were evaluated in the field in Pianxian, Sichuan and Tianshui, Gansu for stripe rust resistance and in Baoding, Hebei and Zhoukou, Henan for leaf rust resistance during the 2012-2013 cropping season. According to the maximum disease severities (MDS) and the area under the disease progress curve (AUDPC), QTLs QPm.caas-4DL, QPm.caas-6BS and QPm.caas-2BL were highly resistant to stripe rust (P < 0.01), which explained 16.9%, 14.1%, and 17.3% of phenotypic variance, respectively. Locus QPm.caas-4DL also showed high resistance to leaf rust (P < 0.01) with phenotypic contribution of 35.3%. Lines that pyramided five (QPm.caas-1A/QPm.caas-4DL/ QPm.caas-2DL/QPm.caas-2BS/QPm.caas-2BL) and four (QPm.caas-1A/QPm.caas-4DL/QPm.caas-2BS/QPm.caas-2BL) QTLs exhibited higher resistance to both stripe and leaf rust compared with their parents. This result indicates that the combination of QPm.caas-4DL (from Bainong 64), QPm.caas-2BS and QPm.caas-2BL (Lumai 21) has a marked effect on improving adult resistance to powdery mildew, stripe rust and leaf rust, and the more QTLs are pyramided, the stronger slow disease resistance can be achieved. In breeding practice, the combination of 4-5 slow mildewing or rusting QTLs can result in durable resistance to multiple diseases.