Spiroplasma citri

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Sweet orange tree infected by Spiroplasma citri (left), causal agent of stubborn, showing stunting as compared to the healthy tree (right). Note the rounded shape of the infected tree.
Author: J.M. Bové, INRA Centre de Recherches de Bordeaux
Source: IPM Images

Spiroplasma citri Saglio et al., 1973 (citrus stubborn)

This spiroplasma is widespread and causes the citrus stubborn disease as well as diseases on various other crops like carrots or sesame. On citrus trees, the symptoms include small, mottled or discoloured leaves, stunting, numerous dead branches and unseasonal blossoms. Fruits are small and can be deformed with a thick rind at the base and a thin rind at the tip. The disease incidence reaches 5-10% in some areas and severely affected trees can show a drop in fruit production of 50% or more. It is naturally transmitted by leafhoppers in a circulative-propagative manner. The main vector species are leafhoppers of the genus Circulifer, e.g. Circulifer tenellus and close relatives. It can be also transmitted through grafting. The disease develops rapidly at hot temperatures (around 30°C).

The establishment of a citrus orchard is critical because the young trees are most attractive to the leafhopper vectors. Therefore, the use of healthy budwood is important for managing the disease. Older trees showing symptoms should be removed and replaced. In hosts other than citrus, the spiroplasma is of little economic significance. However, they might be reservoirs because the leafhopper vector is polyphagous.

Vernacular names
• English: citrus stubborn
• Français: stubborn des agrumes

Spiroplasma citri is the type species of the genus Spiroplasma, a group of wall-less phloem-inhabiting bacteria of the family Spiroplasmataceae and the class Mollicutes. The bacterium can be cultured. It has a characteristic spiral shape and is approximately 2 µm long.