Characterization of Strains of Xanthomonas axonopodis pv. dieffenbachiae from Bacterial Blight of Caladium and Identification of Sources of Resistance for Breeding Improved Cultivars

Abstract

Bacterial blight, caused by Xanthomonas axonopodis pv. dieffenbachiae (Xad), is the most common foliar disease of caladium, an ornamental aroid grown for its colorful foliage. The disease can reduce the marketability of caladiums produced as potted plants and lower the yield of caladiums grown for tuber production. Three bacterial strains were isolated from symptomatic caladiums and identified as Xad using fatty acid analysis, carbon source use, and the sequence of the 16S-23S spacer, and tested for virulence against three susceptible cultivars. Two strains were virulent to all of the cultivars; however, one strain was differentially pathogenic, virulent against two cultivars, but not to the usually highly susceptible ‘Candidum’. In greenhouse inoculation tests of 17 cultivars and one breeding line, four cultivars were ranked as highly susceptible, nine as moderately susceptible, and five as resistant. Ten of these cultivars were also evaluated with natural infection in the field with good agreement between the results of the greenhouse and field evaluations. Cultivars White Queen, Florida Red Ruffles, Florida Sweetheart, Candidum Jr., and Mrs. Arno Nehrling have been identified as resistant to bacterial blight in greenhouse or field evaluations and can potentially be used in future breeding efforts to produce improved cultivars.