Title : Pythium root rot reaction of common bean progenies derived from a molecular marker assisted backcrossing program for anthracnose resistance
Fungal diseases including Pythium root rot and anthracnose are some of the most devastating diseases for common bean (Phaseolus vulgaris) production. Genetic resistance is considered as the most effective control strategy against the diseases. The backcross breeding method has been largely used to transfer Pythium root rot and anthracnose resistance from various resistance sources to elite genotypes which are susceptible. To improve the process of backcrossing in a breeding program, molecular marker-assisted selection (MAS) is being used. Consequently, the breeding program at NaCCRI performed a molecular marker assisted backcrossing program to transfer the Co-42 and Co-5 anthracnose resistance genes from G2333 to a popular susceptible commercial bush bean variety, NABE14. Much as the bean variety NABE14 that was used as the recurrent parent is susceptible to anthracnose, it has Pythium root rot resistance. The objective of this study was to verify if the Pythium root rot resistance allele was also transferred to the selected backcross derived progenies during the backcrossing procedure. Thirty-three NABE14/G2333 BC4 derived progenies were subjected to artificial inoculation with Pythium ultimum var ultimum- Ms 61 in the screen house following a completely randomized design, with two replicates. Genotypes, G2333 (donor parent), NABE14 (recurrent parent), CAL 96 and RWR 719 were included as controls. DNA of the backcross derived progenies and the controls were also extracted following previously reported procedures and the PCR was carried out using the primer PYAA19, which is linked to the Pythium root rot resistance allele. Results of the phenotypic and genotypic evaluation confirmed presence of the Pythium root rot resistance allele in some of the selected anthracnose resistance backcross derived progenies. Common bean lines possessing resistance to both anthracnose and Pythium root rot will be useful in multiple resistance breeding programs.