Phytoplasmas are bacterial plant pathogens that can cause devastating yield losses in diverse low‐ and high‐value crops worldwide (Bertaccini, 2007; Lee et al., 2000). They are obligate symbionts of plants and insects, and in most cases need both hosts for dispersal in nature. In plants, they remain mainly restricted to the phloem tissue (Doi et al., 1967; Whitcomb and Tully, 1989), and spread throughout the plant by moving through the pores of the sieve plates that divide the phloem sieve tubes.
Insect vectors of phytoplasmas are phloem feeders of the Order Hemiptera, mostly leafhoppers (Cicadellidae), planthoppers (Fulgoromorpha) and psyllids (Psyllidae) (Weintraub and Beanland, 2006). In insects, phytoplasmas invade the guts and salivary glands and many other tissues where they can accumulate at great numbers inside and outside cells (Ammar and Hogenhout, 2006). Phytoplasmas have to traverse the gut and salivary gland cells in order to reach the saliva for subsequent introduction into the phloem during insect feeding (Lefol et al., 1994; Lherminier et al., 1990; Nakashima and Hayashi, 1995).
The latent period, i.e. the time between initial acquisition of the phytoplasmas by the insect vector from plants and the ability for the insect to introduce phytoplasmas back into plants, can vary between 7 and 80 days (Moya‐Raygoza and Nault, 1998; Murral et al., 1996). In plants, symptoms can develop at ~7 days after introduction of the phytoplasma by the insect vector, but can take much longer (6–24 months), depending on the phytoplasma and plant species.
