COFFEE LEAF SCORCH BACTERIUM - AXENIC CULTURE, PATHOGENICITY, AND COMPARISON WITH XYLELLA-FASTIDIOSA OF CITRUS

Symptoms of coffee leaf scorch (CLS) appear on young flushes of field plants as large marginal and apical scorched areas on recently mature leaves. Affected leaves drop, shoot growth is stunted, and apical leav es are small and chlorotic. Symptoms may progress to shoot dieback. On ly scorched leaves which could not be related to other known agents co nsistently contained bacteria and bacterial agglomerates when observed with light microscopy. Only plants with these symptoms were positive in enzyme-linked immunosorbent assay (ELISA) tests using antiserum to Xylella fastidiosa Wells et al. The bacterium Xylella fastidiosa Wells et al. was isolated in November 1995 from coffee (Coffea arabica) lea ves with scorch symptoms on supplemented periwinkle wilt medium. Colon ies were circular, dome-shaped, white, and 0.5 to 1.5 mm in diameter. Two of 10 young coffee seedlings stem-inoculated with a suspension of the isolated X. fastidiosa in January 1996 showed leaf scorch symptoms 3 to 5 months later, contained bacteria in xylem extracts, and reacte d positively in ELISA using antiserum to the citrus variegated chloros is (CVC) strain of X. fastidiosa. ELISA-positive bacteria were reisola ted from this plant. None of the symptomless plants, including control s, revealed bacteria on microscopic examinations, ELISA, or isolation attempts. Antisera developed against cultured bacteria from both CLS a nd CVC plants reacted positively against plant extracts of both diseas es in dot immunobinding assays (DIBA). The level of detection was abou t 5 x 10(5) bacteria ml(-1) for both homologous and heterologous react ions. The polymerase chain reaction amplification products produced by CLS and CVC strains of X. fastidiosa were indistinguishable. Geograph ical distribution of these strains is not the same. CLS is widespread and usually occurs if coffee is adjacent to CVC-affected citrus. Howev er, CVC does not always occur when citrus is grown adjacent to CLS-aff ected coffee. The bacteria are closely related, if not identical.