Chapter 15 - The diversity, distribution, and status of phytoplasma diseases in India

Abstract

Phytoplasmas have been reported on diverse plant species in India, including cereals, pulses, vegetables, fruits, ornamentals, palms, sugarcane, oil crops, cotton, medicinal plants, and wild trees. More than 100 new plant species were identified as natural hosts to 11 phytoplasma groups in the past decade. Brinjal little leaf, sesame phyllody, tomato big bud, sugarcane grassy shoot and white leaf, coconut root wilt, and areca nut leaf yellows are the foremost important diseases reported in India. These diseases are related to strains of ‘Ca. P. asteris’, ‘Ca. P. australasia’, ‘Ca. P. aurantifolia’, ‘Ca. P. ziziphi’, ‘Ca. P. trifolii’, ‘Ca. P. sacchari’, and ‘Ca. P. cynodontis’ which are most widespread. Several reports were published documenting the transmission of phytoplasma strains by different leafhoppers, planthoppers, and psyllids. Very recently, three complete draft genome sequences of ‘Ca. P. sacchari’, ‘Ca. P. cynodontis’, and ‘Ca. P. australasia’ strains associated with sugarcane grassy shoot, Bermuda grass white leaf, and sesame phyllody disease completed, opening the possibilities of studies on functional genomics. Mixed infections of two strains of phytoplasmas, virus and phytoplasma, citrus huanglongbing, and phytoplasma are reported. Currently, India's primary focus of research is on pathogen identification, classification, diversity, insect vector identification, natural hosts, and whole-genome sequencing. Presently the suggested effective management practices include roguing, pruning, using resistant varieties, heat therapy, control of insect vectors, and other natural host reservoirs. In this chapter, the history, recent status of phytoplasma diversity and its natural reservoirs are summarized along with prospects of research on phytoplasmas.