Citrus Production: Citrus Nursery Trees Grown in Containers
Most commercial citrus nurseries use grafting to propagate nursery trees. However, there are more than 30 kinds of citrus pathogens which can be transmitted by grafting, via infected budwood. These include citrus greening, tristeza, exocortis, tatter leaf, xyloporosis and psorosis. Once a plant is infected, such diseases may have a serious influence on growth. They shorten the life-span of the orchard and reduce yields and fruit quality.
Citrus-growing areas all over Asia are threatened by viruses and virus-like diseases.
It is important to establish a national or central program to propagate certified nursery trees which are free of virus and other diseases.
There are three major ways in which plants may become infected.
One is via an infected scion when the plant is grafted.
The second is mechanical infection, when tools are used, for example, to prune an infected tree and then used to prune a healthy one, without being sterilized first (tatter-leaf, exocortis and xyloporosis).
The third source of infection is insect vectors which suck the sap of infected trees, and carry the infection to healthy ones. For example, the greening pathogen is vectored by psyllids, while citrus tristeza virus is spread by aphids.
To grow healthy nursery trees, the scion must come from certified disease-free mother stock. Grafting and pruning tools must be sterilized by 1% hypochlorite. Finally, there must be intensive control of insects which are vectors of virus.