Molecular Markers Useful for Detecting Resistance to Brown Stem Rot in Soybean

1989). Other resistance genes may exist. Multiple genes may control BSR resistance in Asgrow A3733 which are Brown stem rot (BSR) causes vascular and foliar damage in soynot derived from known sources of resistance (Waller et bean [Glycine max (L.) Merr.]. Identification of plants resistant to BSR by inoculation with Phialophora gregata (Allington & W.W. al., 1991). Nelson et al. (1989) identified three resistant Chamberlain) W. Gams is laborious and unreliable because of low lines: PI 424.285A; PI 424.353; and PI 424.611A from heritability. Molecular markers linked to the resistance gene could more than 3400 accessions from the USDA Soybean be used to screen for resistant individuals and hasten the development Germplasm Collection. Bachman et al. (1997) screened of BSR resistant genotypes. The objective of this study was to develop 559 soybean accessions from China and found 13 accesmolecular markers for efficient identification of BSR resistant plants sions with resistance to BSR. Most of the publicly rein a breeding program. Seventeen resistant and 29 susceptible cultivars leased BSR resistant cultivars and breeding lines are and plant introductions as well as recombinant inbred lines derived derived from PI 84946-2, including BSR101 which has from a cross between BSR 101 and PI 437.654 were assayed by PCRthe Rbs3 allele (Eathington et al., 1995). Under condibased markers derived from RFLPs K375I-1 and RGA2V-1, Satt244, tions where P. gregata infection affects yield, Sebastian or developed from bacterial artificial chromosome (BAC) sequences. The DNA markers that were developed tag the BSR locus and are et al. (1985) found that in soybean lines derived mostly informative in a diverse range of soybean germplasm. Markers defrom PI 84946-2, BSR resistance was associated with a tected different banding patterns between resistant and susceptible 12 to 16% yield advantage. genotypes. The PCR-based markers will most likely be useful in Molecular markers close to a gene of interest may be screening for BSR resistance and allow soybean breeders to transfer useful for selection in breeding programs, especially for rapidly resistance derived from Rbs3 to improved cultivars or soybean agronomic traits which are difficult to analyze, e.g., dislines. The markers are relatively easy-to-use, inexpensive, and highly ease resistance, insect resistance, and quantitative traits informative. Soybean breeding efforts can now be designed to incorpo(Lawson et al., 1997; Mohan et al., 1997; Heer et al., rate the use of marker information when parental genotypes possess 1998). Selection of genotypes resistant to BSR by inocucontrasting banding patterns. lating plants with isolates of P. gregata is laborious and time-consuming. Moreover, assessment of BSR incidence is rendered difficult by seasonal and environmenB stem rot is a devastating fungal disease of tal variation (Nicholson et al., 1973). Soybean breeding soybean (Glycine max) caused by Phialophora efforts to transfer BSR resistance to improved cultivars gregata, a soil-borne fungus. The pathogen infects host or soybean lines have been hampered by the low heritaplants through the roots and causes vascular and foliar bility (h2 5 0–0.38) of the trait (Sebastian et al., 1985). injury to the susceptible plants (Allington and ChamberSeveral examples of the application of molecular marklain, 1948; Mengistu and Grau, 1986). The disease is ers in breeding programs have been presented. Simple prevalent in soybean producing regions of the northern sequence repeat (SSR) markers have been used for asUSA and Canada (Sinclair and Backman, 1989) and has sessing heterosis in rice breeding (Liu and Wu, 1998). been estimated to cause a yield reduction of over 20 Random amplified polymorphic DNA (RAPD) and semillion bushels each year in the north central states quence characterized amplified region (SCAR) markers alone, depending upon environmental conditions were utilized to characterize anthracnose resistance in (Doupnik, 1993). common bean (Young et al., 1998) and rust resistance Host resistance is the main means of controlling BSR. in sunflower (Helianthus annuus L.; Lawson et al., 1998). Plant introductions (PIs) have been identified as sources Marker-assisted selection (MAS) could facilitate the of non-allelic BSR resistance genes: PI 84946-2 for Rbs1 development of BSR resistant genotypes. MAS is more (Sebastian and Nickell, 1985) and Rbs3 alleles (Eathingefficient than selection based on the phenotype for a ton et al., 1995); PI 437.833 for Rbs2 (Hanson et al., trait with low heritability (Van Berloo and Stam, 1998). 1988); and PI 437.970 for Rbs3 (Willmot and Nickell, Gene introgression can readily be followed using molecular markers, which are not influenced by the environK.L.E. Klos, M.M. Paz and L. Fredrick Marek, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011; R.C. Shoemaker, USDA-ARSmental conditions in which plants are grown. Lewers CICGR and Dep. of Agronomy and Dep. of Zoology/Genetics, Iowa et al. (1999) identified and mapped molecular markers State Univ., Ames, IA 50011; P.B. Cregan, USDA-ARS, Soybean linked with BSR resistance in the soybean cultivar BSR and Alfalfa Research Lab., Beltsville, MD 20705. Research supported 101. This study is a follow-up to Lewers et al. (1999) in by Iowa Soybean Promotion Board. Contribution of the North Central an attempt to develop breeder-friendly markers. Here Region USDA-ARS, Project 3236 of the Iowa Agric. and Home Economics Stn. (Journal Paper no. J-18668), Ames, IA 50011-1010. we report the development and evaluation of nine new Names are necessary to report factually on the available data; however, the USDA neither guarantees nor warrants the standard of the Abbreviations: BSR, brown stem rot; MAS, marker-assisted selection; product, and the use of the name by the USDA implies no approval PCR, polymerase chain reaction; PI, plant introduction; RAPD, ranof the product to the exclusion of others that may also be suitable. dom amplified polymorphic DNA; RFLP, restriction fragment length Received 19 Nov. 1999. *Corresponding author ([email protected]). polymorphism; RIL, recombinant inbred line; SSR, simple sequence repeat. Published in Crop Sci. 40:1445–1452 (2000).