Transmission of Phytoplasmas by Agronomic Practices

Abstract

The propagation materials such as rootstocks, cuttings and other types of grafting materials used as scions play a relevant role in the dissemination of phytoplasma-associated diseases. In particular in the woody plants the propagation material sanitary status plays an important role for both long-distance transmission and disease introduction in the new areas. Since the phytoplasma infection is systemic in the plants, the vegetative propagation of many horticultural crops allows their spread through cuttings, bud wood, tubers, runners and bulbs. It is, therefore, an efficient method of phytoplasma spreading and establishing infection in new plants. Although the phytoplasma spread through vegetative plant propagation occur over short distances by the use of infected propagation materials such as tubers, the worldwide movement of phytoplasmas should be mainly attributed to the man distributing infected propagation materials. The possibility for the phytoplasma vegetative propagation is present in all the shoots and roots comprizing basal shoots, stems, rhizomes, tubers, stolons, corms, buds and bulbs. Some crops like potato, sweet potato, cassava, carrot, onion, garlic, ginger, sugarcane, banana, pineapple, strawberry and many ornamentals like carnations and Chrysanthemum are only vegetatively propagated and hence they have the maximum chances of phytoplasma spread. The fruit tree propagation is usually achieved by grafting or budding of the selected variety onto a suitable rootstock, and this is the main propagation method for the stone and pome fruit trees, grapevine and other fruit trees and shrubs. Also the shoot micropropagation together with grafting, cutting, and other systems to propagate plant germplasm that avoid sexual reproduction is an efficient manner to maintain and transmit the phytoplasma diseases. The importance of phytoplasma infection spread by the vegetatively propagated plants is discussed in this chapter.