Studies on marginal chlorosis of strawberry
Marginal chlorosis has been observed in France since 1988, in all strawberry-growing regions. A similar decline had also been observed in strawberry nurseries in Spain as early as 1984. In nurseries, affected plants showed a red discoloration of the leaves starting from the leaf margins. In fruit production fields, the characteristic symptom was leaf marginal chlorosis. New leaves were also smaller and cup-shaped. Affected plants produced smaller and deformed fruits, and showed root necrosis. Studies done in France showed that an uncultivated phloem-restricted bacterium (γ 3-proteobacterium) was associated with the disease and the name ‘Candidatus Phlomobacter fragariae’ was proposed. A putative planthopper vector, Cixius wagneri (Homoptera: Cixiidae) was then identified. It was also found that field symptoms of strawberry marginal chlorosis were not always associated with ‘Ca. P. fragariae’ but in some cases with stolbur phytoplasma. Using PCR assays, surveys were done in France from 1996 to 2001 on the presence of these two pathogens in strawberry fields and nurseries. Results showed that ‘Ca. P. fragariae’ was predominant in strawberry production fields but that stolbur phytoplasma was predominant in nurseries. In 2001/2002, studies were also carried out on the putative vector. In infected fields, C. wagneri was captured and a high proportion of insects was infected by ‘Ca. P. fragariae’. In cage experiments, naturally infected C. wagneri adults were placed on healthy in vitro grown strawberry plants and were able to transmit ‘Ca. P. fragariae’. The presence of ‘Ca. P. fragariae’ could be detected in these infected plants and some of them showed typical symptoms of marginal chlorosis.
Sources
Foissac X, Danet JL, Zreik L, Salar P, Verdin E, Nourrisseau JG, Garnier M (2004) ‘Candidatus Phlomobacter fragariae’ is the prevalent agent of marginal chlorosis of strawberry in French production fields and is transmitted by the planthopper Cixius wagneri (China).
Acta Horticulturae no. 656, 93-97.