‘Candidatus Phytoplasma australiense’: revision of the EPPO Alert List
So far, only one disease associated with ‘Candidatus Phytoplasma australiense’, the strawberry lethal yellows, appeared on the EPPO Alert List. However, the same phytoplasma has been shown to cause other diseases on various host plants. Therefore, it was felt more appropriate to revise the EPPO Alert List to include the pathogen ‘Candidatus Phytoplasma australiense’ as such, and all the diseases it may cause.
‘Candidatus Phytoplasma australiense’
Why: At first, strawberry lethal yellows disease associated with ‘Candidatus Phytoplasma australiense’ came to our attention because it appeared to us as a 'new' and severe disease of strawberry in New Zealand. Later, it was felt more appropriate to revise the Alert List to include the pathogen as such and all diseases which have been associated to it.
Where: Australia, New Zealand. It is hypothetised that the phytoplasma originates from New Zealand and may have been introduced into Australia.
On which plants:
Cordyline australis (cabbage tree – Agavaceae): ‘Candidatus Phytoplasma australiense is associated with sudden decline of cabbage tree in New Zealand. C. australis is common in forest margins and wetlands and also widely cultivated as an ornamental.
Fragaria ananassa strawberry – Rosaceae): strawberry lethal yellows which occurs in New Zealand, in propagation beds in Kitikati district, Bay of Plenty.
Carica papaya (papaya – Caricaceae): papaya die-back, can be devastating in Queensland but occasional in Northern Territory and Western Australia.
Phormium tenax and P. cookianum (New Zealand flax – Phormiaceae): yellow leaf disease, occurs in New Zealand where a vector has been identified (Oliarus atkinsoni, Homoptera: Cixiidae, monophagous species feeding on New Zealand flax).
Vitis vinifera (grapevine – Vitaceae): Australian grapevine yellows, it occurs in south Australia.
It is also suspected in Coprosma robusta (Rubiaceae), a common shrub in New Zealand.
Note: In New Zealand, Padovan et al. (2000) have also observed that phytoplasmas found in strawberry plants showing symptoms of green petal or lethal yellows were indistinguishable. The fact that the same phytoplasma is associated with two distinct diseases on the same host cannot yet be explained. In addition to New Zealand, it can be recalled that green petal symptoms are seen sporadically in Europe, North America and Australia. In North America, another(?) phytoplasma disease called strawberry lethal decline was reported first in the north western US and then in British Columbia (CA). The pathogen can be transmitted by the leafhopper Aphrodes bicincta. Experimental transmission of western X-disease to strawberry produced symptoms similar to those of lethal decline. Reported to be of minor importance. The only reported control measure is to rogue infected plants. In Australia, another lethal yellows had been associated in the past with a rickettsia-like-bacterium. But this disease has apparently not been seen again. More studies are needed to understand better the aetiology and epidemiology of phytoplasma diseases of strawberry.
Damage: Symptoms usually include leaf yellowing, followed by more or less severe plant decline. Plant mortality has been reported at least on strawberry (severe decline, in field conditions plants may die and in glasshouse conditions they rapidly die), on papaya and Cordyline australis.
Pathway: Infected plants for planting (see host plants above) from New Zealand and Australia.
Possible risks: Among host plants of ‘Candidatus Phytoplasma australiense’, grapevine and strawberry are important crops in the EPPO region. Cordyline australis is also a widely grown ornamental plant (mainly pot plant, but also garden plant in southern parts). Insect vectors are suspected but so far only one New-Zealand species Oliarus atkinsoni has been identified (it does not occur in Europe). The phytoplasma can cause lethal diseases in particular on strawberry, although it is probably of a limited extent (apparently restricted in one region). On grapevine, more data is needed on the impact of the disease in the field.
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EPPO RS 98/171, 2000/162, 2002/102
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Panel review date: 2002-01
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Entry date 1998-09
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Sources
Andersen, M.T.; Longmore, J.; Liefting, L.W.; Wood, G.A.; Sutherland, P.W.; Beck, D.L.; Forster, R.L.S. (1998) Phormium yellow leaf phytoplasma is associated with strawberry lethal yellows disease in New Zealand. Plant Disease, 82(6), 606-609.
Andersen, M.T.; Beever, R.E.; Sutherland, P.W.; Forster, R.L.S. (2001) Association of ‘Candidatus Phytoplasma australiense’ with sudden decline of cabbage tree in New Zealand. Plant Disease, 85(5), 462-469.
Liefting, L.W.; Padovan, A.C.; Gibb, K.S.; Beever, R.E.; Andersen, M.T.; Newcomb, R.D.; Beck, D.L.; Forster, R.L.S. (1998) ‘Candidatus Phytoplasma australiense’ is associated with Australian grapevine yellows, papaya dieback and Phormium yellow leaf diseases. European Journal of Plant Pathology, 104(6), 619-623.
Padovan, A.; Gibb, K.; Persley, D. (2000) Association of ‘Candidatus Phytoplasma australiense’ with green petal and lethal yellows diseases in strawberry. Plant Pathology, 49(3), 362-369.
Padovan, A.C.; Gibb, K.S. (2001) Epidemiology of phytoplasma diseases in papaya in Northern Australia. Journal of Phytopathology, 149(11/12), 649-658.