First report of Xanthomonas axonopodis pv. poinsettiicola in Italy: Addition to the EPPO Alert List
In October 2003, pot plants of poinsettia (Euphorbia pulcherrima cv. Primero) with leaf symptoms were observed in a commercial plant nursery in the province of Latina (Lazio region) in Italy. Symptoms were characterized by black spots surrounded by a yellow halo. In some cases, spots became coalescent. No symptoms were observed on petioles and stems. The causal agent of the disease was identified as Xanthomonas axonopodis pv. poinsettiicola. According to the authors this is the first report of this bacterial disease of poinsettia in Italy, and in Europe. However, according to Wohanka (2004), this pathogen has also been recently found in Germany.
Xanthomonas axonopodis pv. poinsettiicola (Bacterial leaf spot of poinsettia)
Why: Xanthomonas axonopodis pv. poinsettiicola came to our attention, because it was reported for the first time in Europe, as a new leaf spot disease of poinsettia. Although little data is available on this pathogen, more particularly on its epidemiology, geographical distribution and economic impact, the EPPO Secretariat felt that it could present a risk to poinsettia crops.
Where: Leaf spot of Euphorbia pulcherrima was first described in India in 1951, and found later in Florida (USA) in 1962.
EPPO region: Germany (found in one pot plant in September 2003 in Hessen), Italy (first found in 2003 in Lazio).
Asia: Cocos islands, India, Philippines (first reported in 1974)
North America: USA (at least Florida).
South America: Venezuela (first reported in 1996).
Oceania: Australia (Queensland), New Zealand.
On which plants: Mainly on poinsettias (Euphorbia pulcherrima), but E. heterophylla, E. milii, Codiaeum variegatum and Manihot esculenta (all Euphorbiaceae) are also reported as host plants. When the disease was discovered on poinsettia in Florida in the 1960s, it was found that many, if not all, popular cultivars were highly susceptible to the disease, but since then no new work has been conducted to evaluate cultivar resistance.
Damage: Spots are at first visible on the underside of the leaf as grey to brown, water-soaked lesions. As they enlarge to 2-3 mm, they become visible on the upper side of the leaf. Leaf spots are chocolate brown to rust coloured and may be surrounded by a pale green to yellow halo. Spots may coalesce in some cases to form large areas of blighted tissues. Severe infections can cause distortion of new leaves as well as complete yellowing and finally abscission of older leaves. In Florida, it was described as causing commercial losses in outdoor production of poinsettias in the 1960s, but no recent data is available.
Dissemination: Little is know about the epidemiology of the disease, but it has been reported to spread rapidly within a crop, presumably from splashing water. Over long distances, trade of plants of E. pulcherrima can ensure spread of the bacterium.
Pathway: Plants for planting (including cuttings), pot plants of E. pulcherrima.
Possible risks: E. pulcherrima is grown for ornamental purposes in many countries of the EPPO region, particularly indoors. In addition, there is a large trade of propagating material (e.g. rooted cuttings). Control of X. axonopodis pv. poinsettiicola is very difficult in practice, and is almost entirely based on the elimination of all infected plants (e.g. copper compounds are partially effective). Although, data is lacking on the economic impact of this bacterial disease, it may present a risk to poinsettia nurseries and growers in Europe.
EPPO RS 2004/175
Panel review date - Entry date 2004-11
CABI Crop Protection Compendium, 2004.
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