In detail

La tristeza

La tristeza

Tristeza is a viral disease responsible for the disappearance of tens of millions of citrus fruits since the 1930s in large plantations in the southern hemisphere, often with the help of a specific insect, vector of the virus. Its name meaning sadness, was given to it by the peasants of Brazil from this time. It is still a threat today for citrus growing around the world, in particular for trees grafted on bitter orange, Citrus aurantium, the most susceptible rootstock, but also the most widespread for orange trees. There are no means of direct control. Only a preventive action based on the selection of resistant varieties or specific graft-rootstock associations contributes to neutralizing the perverse effect of the virus.

Description of the Tristeza

The Tristeza virus attacks plants of the Rutaceae family, essentially hybrid species and cultivars of the Citrus genus (orange, mandarin, lemon, etc.). The disease results in a significant reduction in vegetation (stunting) and fruit production (size and quantity). The leaves, with a tanned appearance, show chlorosis in the veins. The trunk and branches are subject to peeling of the bark, with the appearance of more or less deep notches, sometimes directly at the level of the graft. Concerning the trees grafted on bigaradier, everything happens as if the responsible virus "triggers" an incompatibility of certain grafts with this rootstock, the consequence being the rapid death of the subject, which is called "quick decline" among the Anglo- Saxons.

Biology and transmission of Citrus Tristeza Virus (CTV)

Citrus Tristeza Virus (CTV) is the pathogen of Tristeza. It is the multiplication of this filamentous phytovirus in the conductive tissue of the elaborate sap called phloem, which generates a profound growth disorder. The virus is transmitted either by vegetative multiplication or grafting in specialized citrus nurseries, or by its main vector, an insect called brown citrus aphid, Toxoptera citricida. We also know that seeds do not transmit the disease. The speed of progression of the citrus brown aphid is around 300 km per year. Since 2005, it has been present in Spain and Portugal, Spain having already lost 20 million trees! All Mediterranean production is currently threatened. It is important to detect the presence of the virus as soon as possible, either by introducing the most sensitive indicator species such as Mexican lime (thin-skinned lime) into the plantations, or by using specific tests using antibodies. monoclonal.

How to fight Tristeza?

Since the direct fight against the CTV virus is impossible, the means of prevention prior to grafting will obviously be preferred. Naturally, if the presence of CTV is confirmed, the destruction of affected trees is compulsory. To replant, it is necessary to obtain healthy and certified plants, chosen from among the rootstocks most tolerant of the Tristeza virus. The population dynamics of the citrus aphid, vector of CTV, must also be monitored and biologically controlled against it. Do not forget, either, the risk inherent in the transport of infected plant materials such as fruits and their peduncles. To overcome this scourge of citrus fruits, it is still necessary to continue efforts to find the ideal rootstock and develop new multiplication techniques such as micro-grafting, free from infection, for example. By C. Schutz Croué