Identification of Molecular Markers Associated with Adult Plant Resistance to Powdery Mildew in Common Wheat Cultivar Massey

1998). Even though race-specific resistance has been extensively used in wheat breeding programs, selection Powdery mildew, caused by Blumeria graminis (DC.) E.O. Speer pressure exerted by cultivars with race-specific resisf. sp. tritici Em. Marchal (syn. Erysiphe graminis f. sp. tritici ), is one of the major diseases of wheat (Triticum aestivum L.) worldwide. tance genes results in the rapid build-up of pathotypes Race-specific resistance has been extensively used in wheat breeding with matching virulence genes. Subsequently, race-speprograms, even though it is ephemeral. Adult plant resistance (APR) cific resistance loses its effectiveness when confronted to powdery mildew is more durable than race-specific resistance. The by pathotypes with matching virulence genes. APR to powdery mildew in winter wheat cultivar Massey has reAnother type of resistance to powdery mildew is mained effective since its release in 1981. A cross was made between called adult plant resistance (APR), which retards infecMassey and a powdery mildew susceptible cultivar Becker. Powdery tion, growth and reproduction of the pathogen in adult mildew severity on F-2 leaves (the second leaf below the flag leaf) plants but not in seedlings. It is also called “slow milof 180 F2:3 lines was rated under natural disease pressure in the field. dewing” (Shaner, 1973) and “partial resistance” (Hautea Among 213 RFLP and 139 microsatellite markers surveyed, 88 (41%) and 90 (65%) markers, respectively, detected polymorphism between et al., 1987). This type of resistance can be identified Becker and Massey. Bulked segregant analysis (BSA) was used to in cultivars with defeated race-specific genes or lacking facilitate the identification of molecular markers associated with APR known race-specific resistance genes. APR to powdery to powdery mildew. Three quantitative trait loci (QTLs), designated mildew is more durable than race-specific resistance. as QPm.vt-1B, QPm.vt-2A, and QPm.vt-2B, were identified with For example, APR in wheat cultivar Knox and its derivinterval mapping. They are located on wheat chromosomes 1B, 2A, atives remained effective against powdery mildew infecand 2B, and, respectively, explained 17, 29, and 11% of the total tion during the 20 yr in which these cultivars were grown variation of F2:3 lines for powdery mildew resistance. The three QTLs commercially (Shaner, 1973). Massey, a derivative of associated with APR to powdery mildew were derived from Massey, ‘Knox62’, was released from Virginia Polytechnic Instiand displayed additive gene action. QPm.vt-2B also fits a recessive model for APR to powdery mildew. In a multi-QTL model, the three tute and State University in 1981 (Starling et al., 1984), QTLs explained 50% of the total variation of F2:3 lines for APR to and still has effective powdery mildew resistance in powdery mildew. The presence of the three QTLs was confirmed with adult plants. 97 recombinant inbred (RI) lines, tested for APR to powdery mildew To improve the efficiency of wheat breeding for APR under natural powdery mildew pressure over 3 yr (F5:6–F7:8 generation). to powdery mildew, it is essential to understand the The molecular markers identified in this study have potential for use genetic basis of APR. Being a quantitative trait, APR in marker-assisted selection and pyramiding of genes for resistance to powdery mildew in wheat is more complex than raceto powdery mildew. specific resistance (Shaner and Finney, 1975). Using monosomic analysis, Chae and Fischbeck (1979) reported that 14 chromosomes were involved in APR to P mildew is one of the major diseases of powdery mildew in the cultivar Diplomat. Both qualitawheat in the world. It is of economic importance tive and quantitative genetic studies indicated that APR especially in areas with maritime or semicontinental to powdery mildew was governed by two to three genes, climate (Bennett, 1984). Yield losses ranging from 13 with moderate to high heritability, in four cultivars, to 34% have been reported (Griffey et al., 1993; Leath Knox 62, Massey, Redcoat, and Houser (Griffey and and Bowen, 1989; Johnson et al., 1979). Resistant cultiDas, 1994; Das and Griffey, 1994b). Hautea et al. (1987) vars offer an effective, economical, and environmentally reported that additive gene effects were the most imporsafe way to control powdery mildew. There are two tant for APR to powdery mildew in four spring wheat types of resistance to powdery mildew. One is called crosses. Das and Griffey (1995) also reported that addirace-specific resistance, which is effective for some isotive gene effects were predominant, but nonadditive eflates of powdery mildew, but ineffective for others. fects also were significant for APR to powdery mildew. Race-specific resistance genes are expressed in seedlings The lack of extensive genetic information hinders the and throughout the vegetative cycle of wheat. Currently, development of effective wheat breeding strategies for 33 alleles at 24 loci have been reported for resistance APR to powdery mildew. The objectives of this study to powdery mildew (McIntosh et al., 1998; Shi et al., were to identify molecular markers associated with APR to powdery mildew in common wheat cultivar Massey, to localize the QTLs to wheat chromosomes, to study C.A. Griffey and M.A. Saghai Maroof, Dep. of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061; Sixin Liu, Dep. of Agronomy and Plant GenetAbbreviations: APR, adult plant resistance; BSA, bulked segregant ics, 411 Borlaug Hall, Univ. of Minnesota, St. Paul, MN 55108. Reanalysis; cM, centimorgan; RFLP, restriction fragment length polyceived. 5 Sept. 2000. *Corresponding author ([email protected]). morphism; QTL, quantitative trait loci; LOD, log likelihood ratio; RI, recombinant inbred. Published in Crop Sci. 41:1268–1275 (2001).