Abstract
Abstract A description is provided for Xanthomonas pelargonii . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Pelargonium spp., also a number of Geranium spp. DISEASE: Bacterial stem rot and leaf spot. The leaf spot phase is characterized by irregular, small, brown, withered, initially water-soaked spots, bordered by a narrow greenish yellow zone, and exuding a small amount of bacterial slime. The stem rot phase gives a brownish black discoloration of the stem tissue and often wilting followed by angular necrosis of the leaves delimited by the main veins. These leaves die back to the stem, but remain attached until finally only the terminal leaves appear healthy. Pythium debaryanum causes very similar symptoms on Pelargonium stems. The fungus, however, produces a blackish-green to almost coal black rot, whereas the bacterium gives a brown to brownish-black rot. The fungal disease progresses much faster. Microscopical examinations reveal fungal mycelium. A Pseudomonas sp. has also been recorded as giving similar symptoms on Pelargonium (Baker, Ministry of Agriculture Technical Bulletin 25: 292, 1972). GEOGRAPHICAL DISTRIBUTION: Widespread in Europe and N. America, also reported from the Middle East and Australia (CMI Map 414, ed. 1, 1966). Additional occurrences include France (44, 3071), Netherlands (11, 767), Romania (46, 1409), Scotland (53, ld), Switzerland (55, 5239), Yugoslavia (54, 4405), Morocco (51, 3809), Iran (49, 910d) and Japan (46, 1947). TRANSMISSION: Under horticultural conditions the disease is spread mainly by operations concerned with vegetative propagation and, in particular, by diseased stock plants, which may appear healthy and by contaminated knives. Water splash dispersal also occurs (34, 369). Transmission by greenhouse whitefly, Trialeurodes vaporariorum , has also been demonstrated (41, 523; 42, 553).
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