Citrus is one of the most popular fruit crops cultivated in Algeria, with an area of 70,503 ha (MADRP, 2019). The major Citrus production regions is situated in the Mitidja area in the Northern region of the country. Stubborn, caused by a pathogen Spiroplasma citri (Gumpf and Calavan, 1981) is the most important world wide disease affecting Citrus (Roistacher, 2004).
The Mollicute Spiroplasma citri belongs to the family Spiroplasmataceae (Gasparich, 2002), is a wall-less prokaryote, Gram positive bacterium (Renaudin, 2006) with mobile helical cells (Whitcomb, 2012).
Citrus stubborn disease (CSD) is particularly important in the hot and semi-arid regions like California, Arizona, most of North Africa (Maroc, Algérie, Tunisie, Libye, Égypte) (Bové, 1995; Nejat el al., 2011), the eastern Mediterranean Basin and the Middle East (Turquie, Syrie, Liban, Palestine) (Bar-Joseph and Catara, 2010; Bové and Garnier, 2000; Roistacher, 2004).
Citrus trees with stubborn disease show characteristic symptoms. Reducing internodes giving the tree a bushy appearance (Bové and Garnier, 2000; Calavan, 1979). Flowering can occur at any time of year. Leaves are small and spoon-shaped and mottled (Bové and Garnier, 2000; Davis et al., 2017; Yokomi et al., 2010). Fruits are deformed, have a gland shape, and aborted or necrotic seeds. The fruits are non-homogeneous in color with a green stylar end, in addition to the presence of lopsided fruits with a curved columella (Bové and Garnier, 2000; Çaglar et al., 2020; Yokomi et al., 2010). The albedo may become blue with unacceptable sensory quality (mainly in grapefruit and tangelos) (Dreistadt, 2012 ; Mello et al., 2010).
The pathogen is phloem-restricted and is transmitted by various species of leafhoppers (Duret et al., 2003) such as Circulifer (syn. Neoaliturus) tenellus (Baker) (Kaloostian et al., 1979); Neoaliturus haematoceps (Mulsant and Rey) (Calavan and Bové, 1989) and Scaphytopius nitridus (Bové, 1995). CSD is also transmissible by grafting (Calavan and Bové, 1989; Gaurivaud et al., 2000; Roistacher, 1991). The spiroplasmas are classified into 38 groups. The plant pathogen Spiroplasma citri belongs to group I-1 (Saglio et al., 1973). In Algeria stubborn disease was reported for the first time in 1952 by Chapot and Delucchi (1964) and in 1980 by Vignault et al. In 2013, it was identified by culturing, ELISA and PCR techniques by Benazzouz (2021). The objective of the work is the study of the prevalence and the diversity of the CSD in Algeria.