A first approach to develop a quantitative screening method to identify resistance to bacterial leaf spot disease caused by Acidovorax anthurii in anthurium

Abstract

Resistance of anthurium cultivars to infection by Acidovorax anthurii, the causal agent of bacterial leaf spot disease was investigated using seven inoculation methods, four inoculum concentrations and two different plant ages towards developing a screening method for identification of disease resistance. Injection of 1 mL of 1.5 × 109 CFU mL−1 three-quarter way down the intact petiole from the intact leaf lamina of a stage-4 leaf consistently and repeatedly elicited 100% infection in susceptible anthurium cultivars, and was the best inoculation method. All 9 measures of resistance using the optimized inoculation method were able to differentiate among 14 anthurium cultivars. Of the three most discriminating measures, proportion of infected leaves per plant showed the largest correlations with field resistance measures obtained through a farm survey and a field trial conducted in a sick plot, and was the best measure of resistance. The study provided evidence for two independent mechanisms of resistance, one at the level of entry and infection establishment and the other at the level of severity of infection. Only two anthurium cultivars showed resistance at both levels. In addition to a cultivar dependent mechanism of resistance, the study showed that there is a general mechanism of mature plant resistance. The study provides a quantitative screening method that can be used to breed for resistance to A. anthurii in anthurium.