World status of phytoplasma diseases associated with eggplant

Brinjal or eggplant (Solanum melongena L.) is an important vegetable crop of sub-tropics and tropics. Among the major biotic constraints, phytoplasmas associated eggplant diseases are major limiting factors affecting its cultivation and yield. Almost all the eggplant varieties under cultivation are susceptible to the phytoplasma disease and caused severe economic losses. Different symptoms associated with disease are reported as little leaf, phyllody, flower virescence, giant calyx, big bud and witches' broom. Several diagnostic methods like Diene's staining, florescence staining and transmission electron microscopy are developed for the localization and detection of phytoplasma bodies in the sieve tubes of phloem tissues of the infected plants. But the PCR based assays along with sequence comparison and RFLP analysis of 16SrRNA gene has been well established and most reliable diagnostic criterions for the phytoplasma identification associated with eggplants. A wide range of genetic diversity was detected among eggplant associated phytoplasmas. Six phytoplasma ribosomal groups (16SrI, 16SrII, 16SrIII, 16SrVI, 16SrIX,16SrXII) were reported to be associated with eggplant from all around the world. The phytoplasma diseases in eggplants are reported to be transmitted by dodder, grafting and through leaf hopper vectors. Moreover, many weed species are reported as alternate hosts of the phytoplasma strains identified on eggplants. No absolute effective control measures of the disease could be developed so far, except resistance, management of insect vectors and altering the dates of sowing to avoid peaks of insect vector population. This review reports an up-to-date account of history, distribution, symptoms, diagnosis, genetic diversity, epidemiology and management of eggplant associated phytoplasma diseases.