Stolbur and MLO
Phytoplasms : Stolbur, Aster Yellow, Purple top...
Causative agent and transmission
At present, we can distinguish two main groups of phytoplasms on the potato:
- diseases belonging to the Stolbur and purple top type (Aster yellow and Purple top);
- diseases belonging to the witches' broom type (Witches' broom).
Phytoplasms, such as the Stolbur, are organisms of the mycoplasma type (or MLO), which are microorganisms close to bacteria but without a wall and which cannot be grown outside a living organism. Stolbur is classified as a quarantine parasite in the European Union.
The main carriers are insects of the leafhopper family (Macrosteles sp., Hyalestes sp.), but transmission is also possible via a parasitic plant : the dodder.
The Stolbur needs a reservoir plant (dodder, tomato, aubergine, henbane, belladonna, datura, field bindweed, etc) as an inoculum because transmission by seed appears non-existent, unlike the witch's broom.
The disease is found in Central and in southern Europe, as well as the Middle East, the United States, Australia, Asia, etc. The disease develops slowly in cool and damp climates.
Symptoms
(clic on photos to enlarge)
• Stolbur and Aster yellow:
On foliage:
- purplish pigmentation of the extremities,
- yellow discoloration with curling up of the young leaves, leaves with upright habit,
- in dry weather, the plants wither and die,
- tubers may appear as well as aerial stolons.
On the underground parts:
- late blight appears on root ends,
- the tubers lose water and become soft, then rot during storage.
The tubers from diseased plants yield thread seed and weak sprouts.
• Witch's broom:
Proliferation of numerous spindly and erect stems.
Detection
Biological indexing (grafting onto indicator plants), Serology, PCR (universal phytoplasma primers or primers specific to the Stolbur), electron microscope.
Control
- Destruction of the carriers (insecticides) and host plants;
- Use of certified seed potatoe
