Coffee leaf scorch bacterium: axenic culture, pathogenicity, and comparison with Xylella fastidiosa of citrus.
The symptoms of coffee leaf scorch (CLS) appeared on young flushes of field plants at Casa Branca, São Paulo, Brazil, as large marginal and apical scorched areas on recently mature leaves. Affected leaves dropped, shoot growth was stunted and apical leaves were small and chlorotic. Symptoms sometimes progressed to shoot dieback. Only scorched leaves which could not be related to other known agents consistently contained bacteria and bacterial agglomerates when observed with light microscopy. Only plants with these symptoms were positive in ELISA tests using antiserum to Xylella fastidiosa. X. fastidiosa was isolated in November 1995 from coffee (Coffea arabica) leaves with scorch symptoms on supplemented periwinkle wilt medium. Colonies 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 reacted positively in ELISA using antiserum to the citrus variegated chlorosis (CVC) strain of X. fastidiosa. ELISA-positive bacteria were reisolated from this plant. None of the symptomless plants, including controls, revealed bacteria on microscopic examinations, ELISA or isolation attempts. Antisera developed against cultured bacteria from both CLS and CVC plants reacted positively against plant extracts of both diseases in dot immunobinding assays (DIBA). The level of detection was about 5 × 105 bacteria/ml for both homologous and heterologous reactions. The polymerase chain reaction amplification products produced by CLS and CVC strains of X. fastidiosa were indistinguishable. The geographical distribution of these strains differ. CLS is widespread and usually occurs if coffee is adjacent to CVC-affected citrus. However, CVC does not always occur when citrus is grown adjacent to CLS-affected coffee. It is concluded that the bacteria are closely related, if not identical.