Marginal chlorosis of strawberries
It was reported in Reporting Service 93/104 (1993, No. 6) that a new bacterial disease of strawberries had been appearing in the European Union, namely in France and in Spain. Further information on this pest has now been published.
In 1990, symptomatic plants were seen in 38 nurseries : over a million plants, of 59 cultivars, representing 35ÿ% of those nurseries' production. Planted out in production fields, this material showed 20ÿ% infection on average in 1991, reacting 90ÿ% on some plots. Main losses occur due to a reduction of sizes of fruits, but not the reduction of number of fruits produced by the plant.
Symptoms of the disease resemble those caused by strawberry mild yellow edge virus and Australian mycoplasma yellows. In nursery plants the first symptoms can be observed in July when leaflets show a red discoloration which starts from the leaf margin and progresses towards the midribs; the leaves develop a cup-like shape. New leaves are reduced in size up to 10% of the normal size and show marginal chlorosis which is 1-2 mm wide. Necrosis of the root system starts at the tip and progresses further towards the internal crown, which stays, however, normal in size and shape. In fruit production the disease can be observed first on young leaves which develop marginal chlorosis and which eventually extends to all leaves of the plant. Leaves are smaller and cup-shaped. The number of fruit is not affected, but the size of them is reduced and they are in general deformed, purple red, sour and very soft rendering them unmarketable. The disease starts on individual plants at an random distribution in the field and spreads to foci in summer. In cases were plastic tunnels were used all plants were infected by the end of the season.
The causal agent, a bacterium like organism (BLO) was observed by electron microscopy to be present in the phloem of affected plants. It has a diameter of 0.2-0.27 æm and a length of 4 æm.
The French authors claim to have observed the disease in Spain (Castilla L‚on area) as early as 1984, but this observation remains subject to proper confirmation.
Nourrisseau, J.G.; Lansac, M.; Garnier, M. ;(1993) Marginal chlorosis, a new disease of strawberries associated with a bacteriumlike organism.
Plant Disease 77, 1055-1059.