Xylella fastidiosa . [Descriptions of Fungi and Bacteria

Abstract

Abstract A description is provided for Xylella fastidiosa . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: The host range is wide. Natural hosts of economic importance include Vitis vinifera, Prunus persica, P. amygdalus, P. saliciana, Morus rubra, Acer rubrum, Quercus rubra and Ulmus americana (Wells et al. , 1987). Medicago sativa (Lucerne/alfalfa) has long been considered a host (53, 635) but unfortunately isolates have not recently been examined. Many other natural hosts have been reported, including Ambrosia artemisiifolia, Ampelopsis arborea, Baccharis halimifolia, Callicarpa americana, Catharanthus roseus, Citrus jambhiri, Fragaria vesca var. californica, Montia linearis, Parthenocissus quinquefolia, Platanus occidentalis, Quercus falcata, Q. laurifolia, Q. nigra, Rhus sp., Rubus procerus, Sambucus canadensis, Solidago fistulosa, Vinca minor and Vitis rotundifolia , many of which are common wild plants in Florida and California (67, 5110; 63, 1898). In addition various plants have been artificially infected in experiments. DISEASE: Pierce's disease of grape, a severe leaf scald and die-back; also causes a leaf scorch of maple, almond, plum, oak, elm, mulberry etc., a wilt in periwinkle and wilting and stunting of ragweed. It also causes phony disease of peach in which trees have a compact appearance due to shortened internodes, come into leaf and flower a little early and have smaller, more highly coloured fruit. The symptoms are not very definite but the disease can be further recognised by cutting root sections and immersing them in acidified methanol (1 ml conc. HCI in 100 ml absolute methanol). Infected roots show purplish spots within a minute or two where vessels contain bacteria. The pathogen inhabits the xylem and produces a toxin. It causes restriction of flow, leading to wilting and scorch, and may produce other symptoms of systemic infection such as chlorosis and stunting. A progressive die-back may be seen with virulent strains and susceptible hosts. GEOGRAPHICAL DISTRIBUTION: USA (California, Florida, GA, NC), Costa Rica, Venezuela ( IMI Distribution Map 262, ed. 3, 1980; 59, 2855; 60, 6035; 66, 2452; 68, 569). Also recently reported from India, but identified only by symptoms and testing with acidified methanol (68, 897). TRANSMISSION: Various leafhoppers have been observed to transmit this disease, including Carneocephala fulgida, Draeculacephala minerva (65, 1977), Graphocephala atropunctata (61, 338), Oncometopia nigricans, Homalodisca coagulata (62, 3417). Lush growth of weeds frequently favours multiplication of these vectors and hence favours spread of any bacteria that may be present.