Biology and Epidemiology

- Survival and reservoir of phytoplasma

Phytoplasma can survive on different cultivated hosts and weeds that form important reservoirs. In the case of "Candidatus Phytoplasma solani", bindweed (Convolvulus arvensis) plays an important role. This micro-organism is rather polyphagous, and it is found in many Solanaceae (tomato, pepper, eggplant, potato, black nightshade, strawberry, celery, carrot ...) which allow it to multiply and thus these hosts form sources of inoculum. The lifecycle of leafhoppers has several larval stages  that occur in  the roots whereas the adult stage is aerial. They also ensure the survival of the phytoplasma from one year to another. As a matter of fact, the phytoplasma may persist in the insect for several generations.


- Transmission and dissemination


The phytoplasma is transmitted in a persistent manner by biting and sap-sucking insects, specifically in the case of stolbur by leafhoppers, Hyalesthes obsoletus. Infections usually happen during the migration period, in late spring and summer (late June, in July). The insect stings in the veins of the phloem to suck juice, and at the same time injects or acquires phytoplasmas. The phytoplasmas, once inside the insect, multiply in the cells of the intestinal layer and pass through it. Then the phytoplasmas  continue to the haemolymph and from there reach various organs, including salivary glands, making infective leafhoppers.

These insects are usually only occasionally found on infected plants. They are able to fly long distances or stay at the same place. The time of appearance of symptoms, which usually takes place 30 to 45 days after infection, depends on the vector migration. Migration is a complex phenomenon resulting from the transfer of insect populations from place to place by a massive flight. The causes of migration are poorly understood. They seem to be related to local conditions unfavourable to leafhoppers. Among the factors that influence migration and the nature of their flights one can mention lack of food, overpopulation, deterioration of the host, photoperiod, endocrine deficiency of insects or genetic effects, temperature and wind. These insects prefer young plants with succulent tissues. During periods of drought, they will move  more easily from natural vegetation to irrigated crops. Sometimes palatability phenomena are observed, but they are poorly understood. Cold winters help to reduce winter populations.

"Candidatus Phytoplasma solani" is not transmitted through seeds in tobacco.