Abstract:
Common bean (Phaseolus vulgaris L) is an important nutritionally rich crop and most
affordable especially for the poor in the developing world. Existing limitations to production
potential include diseases and of particular interest is anthracnose caused by the highly variable
fungus C lindemuthianum that can be best managed through resistant breeding. Therefore, it
was the purpose of this study to identify and evaluate the distribution of pathogenic races,
phenotypically evaluate genotypes, and develop resistant inbred lines with the aid of SCAR
makers.
During the first study, thirty-two isolates were collected in three major common bean
production provinces in South Africa and evaluated in a glasshouse study at ARC-GC. The 12
CIAT differential cultivars were spray-inoculated and evaluated. Eight races of C.
lindemuthianum were identified and were races 3, 6, 7, 81, 83, 89, 263 and 323. Only landraces
AB 136, G 2333, Kaboon, TU and PI 207262 showed complete resistance.
In the second study, two separate field survey trials consisting of 51 germplasm and 26
commercial common bean cultivars were evaluated for reaction to anthracnose in South Africa.
The trials were conducted in RCBD with 3 replications, at Potchefstroom and Cedara. A scale
of 1-9 was used for disease severity evaluation. A total of 92% genotypes were resistant to
anthracnose race 6 in Potchefstroom, on the contrary, in Cedara only 49.35% of genotypes were immune to four C. lindemuthianum races, which were later identified as 7, 81, 83 and 89. Only
25 germplasm were resistant in both locations.
The third study seek to validate a total of five SCAR markers. Three previously reported races
7, 81, and 89 of anthracnose were used to evaluate 26 genotypes and two F2 populations. The
selection of these races was based on the field reaction of genotypes. The F2 generations were
developed with a special interest in the Co-4 locus and associated alleles because of high resistance to anthracnose races. Twenty-three of the genotypes showed complete to partial
resistance and only SW1, RS 7, and Teebus were susceptible. Makers SAS13, SBB14, SY20,
and SCO8 were all loci specific, however, they were not allele specific. SBB12 was loci and
allele specific as a single distinct band was detected in PI 207262 for Co-9.
Overall, the study has shown the presence of a wide geographic distribution of C.
lindemuthianum races, diverse genetic resources, and linkage between the SCAR markers and
Co races of interest for selection breeding in South Arica.
