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First Report of Anthurium Blight Caused by Xanthomonas axonopodis pv. dieffenbachiae in Reunion Island

Xanthomonas axonopodis pv. dieffenbachiae is the causal agent of Anthurium blight, a severe systemic disease of Anthurium. Bacterial blight has been reported in most of the areas where Anthurium is cultivated, especially in Hawaii, California, Guadeloupe, Martinique, Jamaica, and Venezuela. This pathogen is also described on many genera of the Araceae family, e.g., Dieffenbachia, Syngonium, Philodendron, Caladium, Aglaonema, and Colocasia. In Reunion Island, Anthurium blight was first observed in 1997 during routine inspections in two nurseries on Anthurium andreanum plants imported from the Netherlands. Lesions consisted of water-soaked spots at the leaf margins surrounded by chlorotic or necrotic zones. Several necrotic lesions had coalesced to form large, dark patches that covered a large portion of the leaf. Some plants showed symptoms of systemic decay. The disease rapidly spread to other Anthurium plants in the nurseries, causing severe damage. Bacteria, which were consistently isolated from infected plants, were gram negative, yellow-pigmented, and mucoid. Carbon source utilization patterns (Biolog, Hayward, CA) were consistent with Xanthomonas sp. and the bacteria responded positively to monoclonal antibodies raised against X. axonopodis pv. dieffenbachiae (Agdia) in an enzyme-linked immunosorbent assay. Between 1997 and 1999, 114 isolates were collected from three main locations: the two primary infected nurseries and another one found contaminated later. Pathogenicity tests were performed on 8-month-old plants of A. andreanum cv. Carré by infiltrating the leaves with a suspension of bacteria (10⁵ CFU/ml) using a syringe. Each strain was inoculated onto three young leaves (four inoculation points per leaf) on two plants. Control plants received sterile Tris solution. Plants were maintained in a growth chamber at 28°C (±1°C) with 95% (±5%) relative humidity and a photoperiod of 12 h. All 114 strains caused typical symptoms on Anthurium with the development of water-soaked spots near the inoculation point after 9 days, evolving into chlorotic and then necrotic areas after 20 to 24 days. No symptoms developed on control plants. Koch's postulates were completed by reisolating, from all the inoculated plants, bacteria that were again serologically identified as X. axonopodis pv. dieffenbachiae. Since 1997, control measures were adopted, consisting of the destruction of the infected plants and quarantining the contaminated nurseries, as well as surveillance intensification at the ports of entry to prevent new introductions.