Tuesday, November 6, 2007
159-5

Two Cycles of Recurrent Selection for Pyramiding Common Bacterial Blight Resistance in Common Bean.

Robert Duncan1, Shree Singh2, and Robert L. Gilbertson1. (1) Department of Plant Pathology, University of California, Davis, One Shields Av., Davis, CA 95616, (2) University of Idaho, University of Idaho, 3793 N 3600 E, Kimberly, ID 83341-5076

Common bacterial blight (CBB) is one of the most important diseases of common bean (Phaseolus vulgaris L.) and is caused by Xanthomonas campestris pv. phaseoli and X. campestris pv. phaseoli var. fuscans.  Backcross and pedigree methods have commonly been used to breed for CBB resistance, whereas recurrent selection (RS) has not been evaluated for improving CBB resistance.  The objectives of this study were to 1) assess the effectiveness and number of RS cycles required to pyramid high levels of CBB resistance and 2) determine the effect of intermating genotypes with differing levels of CBB resistance for RS.  A double-cross F1 of Wilkinson 2 / DRK 2 // DRK 1 / VAX 3 of 711 plants was used as the base population (C0S0) in this study. Selected resistant by resistant (R x R), resistant by intermediate (R x I), and intermediate by intermediate (I x I) plants were intermated to generate three subpopulations within each RS cycle.  Three subpopulations for each of C0S2, C1S2 and C2S2 were evaluated for CBB reaction in the greenhouse using a randomized complete block design with four replicates in 2006 and 2007.  The CBB resistance improved with each RS cycle in all three subpopulations.  The C2S2 had the highest mean CBB resistance, although mean CBB scores were similar between the R x R and R x I subpopulations.  Moreover, the greatest number of resistant recombinants were produced in the C2S2 R x R subpopulation, followed by the C2S2 R x I and I x I subpopulations.  At least one cycle of recurrent selection was needed to produce a family with a mean CBB-resistant score. Additionally, it was possible to pyramid a high level of CBB resistance using RS among the C0S0 recombinants with an intermediate CBB reaction.