Citrus bacterial spot

Scientific name

[Bacterium] Xanthomonas alfalfae subsp. citrumelonis (syn. Xanthomonas axonopodis pv. citrumelo)

Other common names

CBS, this however may lead to confusion since citrus black spot uses the same abbreviation.

Disease cycle

Citrus bacterial spot is only known to occur only under nursery conditions. There are three groups of isolates based on laboratory assays considered aggressive, moderately aggressive, and weakly aggressive. Only aggressive isolates were historically spread in field nurseries naturally by wind-blown rain and overhead irrigation. All strains can be mechanically moved from tree to tree under normal nursery operation. When infected trees are transplanted into groves, the bacterium rapidly dies off and the disease becomes undetectable in a few months. The activity of the citrus leaf miner exacerbates citrus bacterial spot.

Symptoms

Leaf - the symptoms of citrus bacterial spot are very similar to those of citrus canker, but the lesions are flat and not raised. Foliar lesions show necroticnecrotic:
a cell, group of cells, or tissue that has suffered a rapid destruction and quick death; typically localized and may be caused by injury, radiation, chemicals, toxic substances, or microbiological interactions
centers that often can crack or drop out and are surrounded by water-soaked margins. Lesions produced by aggressive strains have more pronounced water-soaked margins than those of citrus canker. Budbud:
a.) a small lateral or terminal projection on the stem of a plant, often enclosed by protective scales, from which shoots, leaves, or flowers develop b.) an undeveloped shoot, leaf, or flower c.) an outgrowth from an organism that creates a new individual (asexual reproduction)
take and growth on infected rootstocks, especially Swingle, can be infected.

Fruit - fruit infection is rare and has only been reported on Flying-dragon trifoliate.

Host range

Citrus bacterial spot can affect common scionscion:
young shoot or twig of a plant that is grafted onto the rootstock of another plant, usually a related species
and rootstockrootstock:
a living plant, sometimes just the stump, with a healthy, established root system, used for grafting a cutting or budding from another plant; the grafted portion is called the scion
species and is most severe on Swingle citrumelo, trifoliate orange rootstockrootstock:
a living plant, sometimes just the stump, with a healthy, established root system, used for grafting a cutting or budding from another plant; the grafted portion is called the scion
, and grapefruit scions.

Distribution

Only known to occur in Florida.

Easily confused with

Citrus canker

It should be noted that citrus bacterial spot was initially regulated in Florida similarly to citrus canker, however, the low disease potential in groves was realized and the disease was deregulated. Care must be taken to differentiate between citrus bacterial spot and citrus canker.