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Symptoms of P. marginalis pv. marginalis on lettuce start with the limited wilting of leaf margins (marginal leaf blight). The wilted areas may consist of small spots of up to 2-3 cm. In later stages, these spots become dry yellow-brown to black necrotic. Vascular bundles of wilting leaves show a brown to black necrotic discolouration. The vascular discolouration may also occur in the early stages of wilting. The formation of pink discoloured basal portions of mid veins (pink rib) in stored lettuce may also occur (Hall et al., 1971).
On chicory and endive, the first symptoms are small, brown to black wet spots on the leaves that enlarge under humid weather conditions, turning into large, wet, brown to black necrotic lesions. In later stages, the disease may also progress through the veins, and leaves may wither and die. Young leaves may stay healthy for some time, but finally rot from the base of the plant. In dry weather, disease progress may stop.
Cavity formation in vascular root tissue, root and crown rot of sainfoin, was described by Gaudet et al. (1979, 1980).
A postharvest disease on tomatoes (green and red), cabbage, onions and carrots may occur. This consists of a soft rot, starting with slightly sunken, watersoaked, light to dark lesions (Bartz, 1979; Sale, 1991)
A severe black, wet head rot of unwounded inflorescences of broccoli has been described (Wimalajeewa et al., 1987).
To avoid losses during storage due to soft rot caused by P. marginalis pv. marginalis, damage should be avoided as much as possible and low storage temperatures (close to 1°C) and low humidity should be maintained (Wright, 1993). Controlled storage atmosphere (with higher carbon dioxide levels) may possibly reduce storage rots of tomato (Ibe and Grogan, 1983; Barriga et al., 1989). Postharvest fungicide drenches may enhance the incidence of soft rot caused by P. marginalis pv. marginalis (Geeson and Brown, 1979).
In cabbage for winter harvest in Japan, covering crops with cheesecloth at a height of ca 50 cm, or using a frost protective fan, proved to be effective in reducing losses due to head rot (Igarashi, 1994).
Lower nitrogen-fertilizations and crop lifting at >90% top-down (fully mature), avoiding wounding during harvest, grading as much as possible, and covering and drying before storage, helped to reduce storage rot of onions (Wright, 1993).
Weekly applications of stone meal Silkaben or calcium chloride during head formation in broccoli has been shown to reduce head rot by 50 and 33%, respectively.
There is a considerable variation in susceptibility to marginal leaf blight in lettuce varieties and broccoli, but apparently only a few resistant varieties occur (Miller, 1980; Canaday and Wyatt, 1992; Neuvel et al., 1996).
Crop losses of up to 40% due to head rot in broccoli have been reported from Canada by Hildebrand (1989). Wimalajeewa et al. (1987) reported a 35% crop loss in the field and over 10% in transit and storage for broccoli with head rot. Severe problems in the field and in storage with onions have been reported from New Zealand (Wright and Hale, 1992).
Economic losses arise from reduced marketability of the crop, the presence of diseased stored product, and yield reduction. There are no data available on the economic importance of rots in the field and in storage caused by fluorescent pseudomonads, including P. marginalis pv. marginalis in the European area. In many cases they only appear to be opportunistic pathogens.