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Review
. 2019 Jun 27:10:1349.
doi: 10.3389/fmicb.2019.01349. eCollection 2019.

Global Status of Phytoplasma Diseases in Vegetable Crops

Shweta Kumari  1 , Krishnan Nagendran  1 , Awadhesh Bahadur Rai  1 , Bijendra Singh  1 , Govind Pratap Rao  2 , Assunta Bertaccini  3
Affiliations
Review

Global Status of Phytoplasma Diseases in Vegetable Crops

Shweta Kumari et al. Front Microbiol. .

Abstract

The presence of phytoplasmas and their associated diseases is an emerging threat to vegetable production which leads to severe yield losses worldwide. Phytoplasmas are phloem-limited pleomorphic bacteria lacking the cell wall, mainly transmitted through leafhoppers but also by plant propagation materials and seeds. Phytoplasma diseases of vegetable crops are characterized by symptoms such as little leaves, phyllody, flower virescence, big buds, and witches' brooms. Phytoplasmas enclosed in at least sixteen different ribosomal groups infecting vegetable crops have been reported thus far across the world. The aster yellows phytoplasma group (16SrI) is presently the prevalent, followed by the peanut witches' broom (16SrII). Wide and overlapping crop and non-crop host ranges of phytoplasmas, polyphagous insect vectors, limited availability of resistance sources and unavailability of environmentally safe chemical control measures lead to an arduous effort in the management of these diseases. The most feasible control of vegetable phytoplasma diseases is a consequence of the development and implementation of integrated disease management programs. The availability of molecular tools for phytoplasma identification at the strain level greatly facilitated this kind of approach. It is moreover essential to understand the molecular basis of phytoplasma-vector interaction, epidemiology and other factors involved in disease development in order to reduce the disease outbreaks. Information on the knowledge about the most widespread phytoplasma diseases in vegetable crops is reviewed here in a comprehensive manner.

Keywords: aster yellows; management; phytoplasmas; symptoms; vegetables.

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Figures

FIGURE 1
FIGURE 1
Symptoms in vegetable crops. (A) Little leaf in brinjal; (B) close up view of brinjal flower showing phyllody; (C) big bud in tomato; (D) witches broom’ in Cucurbita pepo; (E) flat stem in lettuce; (F) witches’ broom in chili; (G) witches’ broom in potato; (H) witches’ broom in cabbage; and (I) flat stem in cowpea.
FIGURE 2
FIGURE 2
Phylogenetic tree, based on phytoplasma 16S rDNA, showing the relationships among representative of the phytoplasma strains infecting vegetables and related ‘Candidatus Phytoplasma’ species (‘Ca. P.’). The tree is constructed by neighbor joining method using Mega 6.0 software. GenBank accession numbers are specified in the tree together with ribosomal group or subgroup indication. Numbers on branches are bootstrap values obtained for 1,000 replicates.
FIGURE 3
FIGURE 3
Various phytoplasma groups infecting vegetable crops.
FIGURE 4
FIGURE 4
Distribution of phytoplasma diseases in different vegetable crops.
FIGURE 5
FIGURE 5
Geographical distribution of phytoplasmas in vegetable crops.
FIGURE 6
FIGURE 6
Possible strategies available for the management of phytoplasma diseases in vegetable crops.
See this image and copyright information in PMC

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