Identification of Genes for Resistance to Bean Common Mosaic Virus and Bean Common Mosaic Necrosis Virus in Snap Bean (Phaseolus vulgaris L.) Breeding Lines Using Conventional and Molecular Methods

Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV) are among the biggest threats for snap bean production in Bulgaria due to their seed, aphid and mechanical transmission. Old valuable Bulgarian snap bean varieties are being neglected, because of the high percentage of virus-infected seeds. Breeding resistant cultivars is the best way to solve the problem. The genetic control towards both viruses is assured by one dominant I gene and a number of recessive (bc-u, bc-1, bc-1(2), bc-2, bc-2(2) and bc-3) genes. Our aim was to identify resistance gene combinations in advanced F8 breeding lines, derived from two crosses (A-8-40-7-2-1xIVT 7214) and (ZariaxRH 26D), by the application of conventional and molecular approaches. Four methods were applied for the characterization of their resistance gene makeup: (i) leaf-abscission infection test designed to identify I gene by direct inoculation with NL3 strain of BCMNV; (ii) intact-plant infection test with strain NY15 of BCMV to separate immune genotypes, possessing bc-ubc-1(2), bc-ubc-2(2,)bc-ubc-2bc-3, I, Ibc-1(2), Ibc-2(2) or Ibc-3; (iii) PCR analysis with the following markers: SCAR - SW13 (for I gene), SBD5 (for bc-1(2)), ROC11 (for bc-3) and CAPS - eIFE4 (for bc-3); and 4) high-temperature (more than 30 degrees C) infection test with NL3 of BCMNV to provoke systemic necrosis in I, Ibc-1, Ibc-1(2), Ibc-1(2)bc-2(2) or Ibc-3. The four methods applied worked properly and complemented each other. Valuable gene combination (Ibc-3) was established in seven breeding lines with immune reaction to BCMNV. They will be included in the snap bean breeding programme for virus resistance.