Abstract
While random amplification of polymorphic DNA (RAPD) markers linked to disease resistance genes have been widely used in plant breeding programs, they generally lack reproducibility. To overcome this major disadvantage and other drawbacks, RAPD markers can be converted into sequence characterized amplified region (SCAR) markers, which are genetically defined loci amplified by polymerase chain reaction (PCR) using specific primers. Thus, SCAR markers are typically more reproducible than RAPD markers, due to specific amplification of genomic regions. In this study, a previously identified RAPD marker AT9/917 that is linked to the Puccinia psidii Winter (rust) resistance gene 1 (Ppr1) in Eucalyptus grandis was successfully converted into a specific SCAR marker. Seven specific SCAR primers were designed based on cloning and sequencing of the RAPD marker AT9/917. Different pairs of SCAR primers were tested in an E. grandis family from a crossing between a resistant and a susceptible E. grandis. Prime pair SCAR AT99151L and AT9915914R produced amplicons of expected size. Restriction enzyme digestion of the amplicon revealed polymorphisms between the resistant and susceptible parents. Association analysis between phenotype (rust resistance) and SCAR genotypes in the E. grandis family suggests that this specific SCAR is useful for marker-assisted selection of E. grandis trees resistance to P. psidii Winter. Key words: Plant breeding, molecular markers, random amplified polymorphic DNA (RAPD), Mark-assisted selection, sequence characterized amplified region (SCAR).
Highlights
From as early as the 1970’s, eucalyptus rust, caused by Puccinia psidii Winter, has posed great threats to eucalyptus trees in Brazil
To overcome this major disadvantage and other drawbacks, random amplification of polymorphic DNA (RAPD) markers can be converted into sequence characterized amplified region (SCAR) markers, which are genetically defined loci amplified by polymerase chain reaction (PCR) using specific primers
A previously identified RAPD marker AT9/917 that is linked to the Puccinia psidii Winter resistance gene 1 (Ppr1) in Eucalyptus grandis was successfully converted into a specific SCAR marker
Summary
From as early as the 1970’s, eucalyptus rust, caused by Puccinia psidii Winter, has posed great threats to eucalyptus trees in Brazil. Control of P. psidii rust has been successfully accomplished by planting resistant genotypes of trees obtained by intra-and interspecific breeding or by selection of genotypes with fast initial growth. In the latter approach, fast-growing plants experience less time exposed to the P. psidii pathogen in the field (Alfenas et al, 2004; Krugner and Auer, 2005). Identification of the molecular markers linked to the disease resistance genes has emerged as an important tool for the selection of disease resistant genotypes These markers allow us to identify disease resistant characteristics, even in the absence of causative pathogens (Benet et al, 1995). We converted a previously identified RAPD marker into a SCAR marker, and evaluated its usefulness in selection of rust resistant genotypes
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