Identification of Field Resistance to Bacterial Leaf Spot Disease of Anthurium under Natural Epiphytotics in Trinidad

Abstract

Six anthurium cultivars, grown widely in Trinidad were evaluated for field resistance to Acidovorax anthurii, the causal agent of bacterial leaf spot disease (BLS), in a disease nursery to determine whether resistance/tolerance to BLS can be reliably assessed in field studies. The experiment was arranged in a randomized complete block design with four replications and with 25 plants per replicate per cultivar. Data on time to first symptoms, cumulative number of diseased leaves and cumulative number of dead plants per replicate per cultivar was recorded on a monthly basis over a 12-month period. Cubic polynomials were fitted for cumulative number of diseased leaves and cumulative number of dead plants per replicate for each cultivar and the largest slopes obtained during the exponential phase were investigated for the two parameters. The validity of resistance measures were assessed by correlating to field resistance assessed from a farm survey in another study. Time to first symptoms was found to be independent of the cultivar’s BLS resistance score. Cultivar differences for cumulative number of diseased leaves and dead plants were significant (P < 0.001) at 12 months after planting (MAP), with a strong correlation between them (Pearson’s r = 0.84, Spearman’s r = 0.89, P < 0.05). The largest rates of disease progression in leaves or disease progression measured as plant death over time were higher in the susceptible anthurium cultivars compared with the moderately resistant ones. Cumulative number of diseased leaves at 12 MAP was more discriminatory among cultivars and showed a larger correlation with field resistance scores obtained from the island-wide survey than cumulative number of dead plants and is therefore proposed as the reliable measure for assessing field resistance to BLS. The use of this method for breeding anthurium for BLS resistance is discussed.