Development of sequence characterized amplified region (SCAR) markers linked to race-specific resistance to <i>Striga gesnerioides</i> in cowpea (<i>Vigna unguiculata</i> L.)

Abstract

An amplified fragement length polymorphism (AFLP) fragment, E-ACT/M-CAA524, tightly linked to the Striga gesnerioides race 1 (SG1) resistance gene Rsg-2-1 in cowpea (Vigna unguiculata L.) was isolated by polyacrylamide gel electrophoresis, cloned, and its nucleotide sequence determined. Based on the resulting sequence information, a pair of sequence specific primers were designed and used to isolate identical and similar fragments from cowpea genomic DNA of different cowpea lines by polymerase chain reaction (PCR) amplification. The primers amplified a ~500 bp fragment (SCAR marker designated as 61R) that was present in the resistant parent TVU14676, absent in susceptible parent IT84S-2246, and segregated with the resistance phenotype in an F₂ population, derived from a cross of these two genotypes. The same primers were used to isolate a fragment similar to 61R from another S. gesnerioides resistant line Kvx 61-1. The sequence of this fragment was used to design a new combination of primers that developed a second SCAR marker, designated as 61R-M2. Subsequent analysis of the three markers, E-ACT/M-CAA₅₂₄, 61R and 61M2 showed that they are linked to each other by 0.6 centimorgans (cM). The utility of these SCARs in marker assisted selection programs for cowpea was discussed.

Keywords: Striga gesnerioides, centimorgans (cM), race specific resistance, amplified fragment length polymorphism (AFLP), sequence characterized amplified region (SCAR), marker assisted selection (MAS)