First Report of Xanthomonas axonopodis Infecting Agapanthus in Florida

• Published in: Plant disease Vol. 86; no. 5; p. 562
• Main Authors: Norman, D J, Henny, R J, Yuen, J M F, Dickstein, E R
• Format: Journal Article
• Language: English
• Published: United States 01.05.2002
• ISSN: 0191-2917
• DOI: 10.1094/PDIS.2002.86.5.562A

Agapanthus praecox subsp. orientalis, commonly called African lily or lily-of-the-Nile, bears large, round, blue or white flowers above attractive dark green foliage. Because of these horticultural features, this member of the family Liliaceae, has become a popular perennial bedding plant. For the past 2 years during warm wet periods, symptoms of chlorotic, water-soaked, leaf-streaks have been observed on agapanthus production in Florida. Round butyrus, bright yellow colonies were consistently isolated on nutrient agar. Bacteria were characterized as gram negative, catalase positive, motile, strictly aerobic, and not hydrolytic on starch. Using fatty acid analysis (FAME) and the MIDI Microbial Identification System with software version TSBA 3.90 (Microbial ID, Inc., Newark DE), three strains were further characterized and identified as Xanthomonas axonopodis with similarity coefficients to X. axonopodis pv. dieffenbachiae (0.907, 0.915, and 0.944) and to X. axonopodis pv. poinsetticola (0.912, 0.922, and 0.916). The three isolates were each inoculated on three plants each of agapanthus cv. Blue African lily, Dieffenbachiae maculata cv. Camille, and poinsettia, Euphorbia pulcherrima cv. PeterStar Red. Plants were sprayed with a suspension of each isolate at 1 × 10 CFU/ml, bagged for 24 h to raise humidity, and placed in a glasshouse for symptom development. Strains of X. axonopodis pv. poinsetticola (NZTCC 5779) and X. axonopodis pv. dieffenbachiae (X1718) were used as positive controls. Within 3 weeks, isolates from agapanthus produced leaf streaks on agapanthus plants, small, scattered, water-soaked lesions on dieffenbachia leaves, and no symptoms on poinsettia. No symptoms developed on the agapanthus plants when inoculated with either control strain. Both control strains formed lesions on leaves of their original host species. Xanthomonas was reisolated from treatments with symptomatic leaves. Plant inoculations were repeated with similar results. Although the agapanthus isolates were highly similar in FAME profiles to X. axonopodis pv. dieffenbachiae, symptoms produced on dieffenbachia were mild as compared with those produced by the dieffenbachia isolate. Therefore, these isolates may represent a distinct pathovar.