Development of SCAR markers linked to common bean angular leaf spot resistance genes
Angular leaf spot (ALS), caused by fungus Phaeoisariopsis griseola (Sacc) Ferraris, is considered the most important disease in many common bean (Phaseolus vulgaris) growing areas. ALS in Brazil is responsible for significant yield losses. The development and use of resistant cultivars is considered to be the most viable method for controlling this disease. The use of molecular markers linked to the resistance genes can be very useful to monitor these genes in breeding programs. Several RAPD markers linked to ALS resistance have been identified, however, this type of marker is sensitive to PCR amplification conditions, which reduce its reproducibility among different laboratories. SCAR markers, on the other hand, are highly specific RAPD-derived markers which do not show such limitations. The objective of this work was to develop SCAR markers from RAPD markers previously identified as linked to ALS resistance genes Phg-ON (markers OPBA16, OPAA19, and OPM02) and Phg-1 (marker OPH13), present in different common bean cultivars (Carvalho et al., 1998; Faleiro et al., 2003). The RAPD markers were amplified, fractionated in 1.5% agarose gels, the bands of interest were excised and purified with the Gel Extraction Kit (QIAgen), and cloned into the pGEM-T Easy vector (Promega). After transformation of competent DH5 á Escherichia coli cells, the positive clones (white colonies) were confirmed by PCR. The clones were sequenced in an ABI Prism 377 (Perkin Elmer), the SCAR primers were designed, synthesized and tested in populations segregating for genes Phg-ON or Phg-1 (Table 1). The amplification conditions are described on Table 2. These SCAR markers can now be used in marker assisted common bean breeding programs. They are presently being in the BIOAGRO/UFV breeding program, which aims to pyramid disease resistance genes in different commercial bean varieties.