Screening of the AFLP Markers Associated to the Resistance Locus of Cucumber alternaria leaf spot and Its Conversion to SCAR Marker

The study screened the molecular marker linked to the cucumber alternaria leaf spot resistant gene, and discussed the molecular method for identification and selection of resistant materials. With a F2 population derived from F1 of L63 (susceptible female) and L9 (resistant male) was used as materials, their resistance to alternaria leaf spot of cucumber were identified through seedling inoculation. The results indicated that the resistance to alternaria leaf spot was controlled by a pair of recessive gene, and the susceptible was in the mode of incomplete dominant inheritance. The polymorphism between resistant and susceptible bulk of cucumber alternaria leaf spot were studied using BSA method and AFLP technology. 1 024 AFLP markers were screened, and a co-dominant marker E-AT/M-TCT was obtained. Sequencing of the polymorphic fragment indicated that their lengths were 246 bp and 251 bp, respectively, and they were orthologous sequences with an insertion/deletion of five nucleotides. The resistant and susceptible F2 plants possessed the 246 bp and the 251 bp fragments, the mid-plants possessed both two fragments. The marker was closely linked to the cucumber alternaria leaf spot resistance-related gene, and the genetic distance between the marker and the gene was 4.96 cM. According to its sequencing result, the AFLP marker was further converted into SCAR marker.