Sequence characterized amplified regions linked to rust resistance genes in the common bean

Uromyces appendiculatus (Pers.) Unger, the causative fungus of rust in comm on beans (Phaseolus vulgaris L.), consists of many pathotypes or pathogenic races. Cultivar Ouro Negro is resistant to most pathotypes detected in Bra zil in the last few decades. We attempted to identify molecular markers lin ked to a rust resistance gene block present in Ouro Negro. DNA samples extr acted from homozygous near isogenic BC3F2:3 lines derived from a cross betw een susceptible cultivar US Pinto 111 and Ouro Negro were grouped, followin g greenhouse inoculations, into two contrasting bulks, one containing only resistant and the other only susceptible plants. The bulks were amplified w ith 605 random primers and two of them amplified bands which were heteromor phic between the two bulks. These random amplified polymorphic DNA (RAPD) b ands were transformed into sequence characterized amplified regions (SCARs) SCARBA08 and SCARF10. The rust resistance-susceptibility phenotypes and th e molecular genotypes with the two SCAR markers of 303 F-2:3 families from US Pinto 111 x Ouro Negro were determined. SCARBA08 and SCARF10 were determ ined to be 4.3 +/- 1.2 and 6.0 +/- 1.3 centimorgans (cM) from the rust resi stance locus, respectively. These markers are being used in combination wit h other markers for resistance to rust, anthracnose, and angular leaf spot previously identified in our laboratory to aid the indirect selection of de sirable plants in segregating populations in which Ouro Negro has been used as donor parent.