Selecting for common bacterial blight resistance in common bean: effects of multiple leaf inoculation and detached pod inoculation test

Breeding for resistance is an important strategy to manage common bacterial blight disease caused by Xanthomonas campestris pv. phaseoli (E. Smith) Dye (Xcp) in common bean (Phaseolus vulgaris L.). It is necessary to determine if prior inoculation of the first trifoliolate leaf with Xcp influences subsequent reactions in other plant organs by increasing or decreasing resistance to Xcp. It is difficult to get an accurate estimate of heritability of disease reaction in pods since environment greatly affects the heritability estimate if flowering occurs over extended time periods. Thus, the disease reaction in attached pods versus detached pods was compared. A split-split plot design with two replications (growth chambers as blocks) was used, with bean lines as the whole-plot factors, Xcp strains as subplot factors, and bacterial inoculation treatments for leaf reactions or pod treatments as split-split factors. The first trifoliolate leaves, later developed leaves, and attached and detached pods were inoculated. No effects of prior inoculation on the disease reactions of subsequently inoculated leaves and pods were observed, indicating that the different plant organs can be inoculated at different times. The fact that detached and attached pods showed similar disease symptoms would suggest use of the former to reduce environment variance and improve heritability estimates of resistance