First report of a strawberry disease resembling ‘marginal chlorosis’ in Italy
In autumn 2005 and 2006, strawberry plants showing symptoms resembling those of ‘marginal chlorosis’ were observed in nurseries and strawberry fields in several provinces of Emilia-Romagna, Italy. Marginal chlorosis is an infectious disease which was reported in France and found to be associated with a γ-3 proteobacterium (‘Candidatus Phlomobacter fragariae’) and stolbur phytoplasma (‘Candidatus Phytoplasma solani’ - EPPO A2 List). In France, ‘Ca. P. fragariae’ was considered to be the prevalent agent of the disease in the field (see EPPO RS 2005/104).
In Italy, affected strawberry plants showed conspicuous stunting and poor root systems. Older leaves showed upward rolling and a marked purple discoloration, while young leaves were cupped, chlorotic, generally reduced in size with shortened petioles. Leaf samples were collected and tested by PCR for the presence of ‘Ca. P. fragariae’ and ‘Ca. P. solani’. 13 field samples (out of 36) and 1 nursery sample (out of 31) tested positive for the presence of ‘Ca. P. fragariae’. 21 samples from nurseries and 5 from production fields tested positive for ‘Ca. P. solani’. Molecular studies (comparisons of sequences of PCR products and of the 16S rDNA gene) showed that the γ-3 proteobacterium isolated from strawberry in Italy presented higher sequence homology with the ‘syndrome des basses richesses proteobacterium*’ than with ‘Ca. P. fragariae’. Further work is being carried out in Italy to investigate incidence, geographical distribution, epidemiology, and host range of this γ-3 proteobacterium found on strawberry.
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* Syndrome des basses richesses is a disease of sugar beet characterized by a low sugar content in the roots which was first reported in France in 1991. It is also of complex etiology, being associated with ‘Ca. Phytoplasma solani’ and with a γ-3 proteobacterium closely related to, but distinct from, ‘Candidatus Phlomobacter fragariae’. In sugar beet fields, ‘syndrome des basses richesses’ is transmitted by ciixid insects (see also EPPO RS 2008/083).
Sources
Terlizzi F, Babini AR, Lanzoni C, Pisi A, Credi R, Foissac X, Salar P (2007) First report of a γ 3-proteobacterium associated with diseased strawberries in Italy. Plant Disease 91(12) p 1688.