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The forest of Southern India, especially in the states of Karnataka, Tamil Nadu and Kerala are recognised for natural populations of sandalwood contributing 90% of its distribution in India. The sandal spike disease (SSD) of sandalwood is known to be associated with the presence of aster yellows (‘Candidatus Phytoplasma asteris’, 16SrI-B). The recent survey and collection of the symptomatic sandalwood samples from the Marayoor sandalwood reserve of Kerala state confirmed the presence of this phytoplasma; however, also 16SrXI-B phytoplasmas were identified. These phytoplasmas were present in single or in mixed infection in the collected sandalwood, sugarcane and Indian gooseberry samples from this area. This study is the first report of 16SrXI-B phytoplasmas in sugarcane in Kerala of witches’ broom disease in Indian gooseberry associated with aster yellows phytoplasmas and the first report of 16SrXI-B phytoplasma presence in SSD plants. These findings unveil serious threat to existing sandalwood and sugarcane cultivation in the Marayoor sandalwood reserve area, and demand a thorough investigation on phytoplasma insect vectors to efficiently manage these diseases associated with phytoplasmas.

Marigold plants with suspected symptoms of phytoplasma infection were collected during field surveys from three different districts of Karnataka where the incidence of these symptoms was ranging from 1 to 11%. The presence of phytoplasmas in the samples showing phyllody and virescence symptoms was confirmed by nested PCR assays using P1/P7 and R16F2n/R16R2 phytoplasma specific primer pairs. The nucleotide sequence identity and phylogenetic analyses of the 16S rRNA gene sequence indicated the presence of a ‘Candidatus Phytoplasma australasia’ -related strain in the diseased marigold samples. The phylogenetic analysis of secA gene sequences of this phytoplasma strain showed its clustering with strains enclosed in the 16SrII-D subgroup, confirming the phytoplasma identification. To the best of our knowledge, this constitutes the first report of 16SrII phytoplasmas associated with marigold phyllody from the Karnataka state. As the most widely cultivated commercial flower of Karnataka, marigold has a significant role in the national and international flower trade. Phyllody and associated symptoms have a direct negative impact on the quality and market value of these flowers.

The sandal spike disease of sandalwood is known to be associated with aster yellows (AY) phytoplasmas and is a prime threat to sandalwood cultivation in India. The Marayoor Sandalwood Reserve (Kerala state) has an excellent collection of naturalised and matured sandalwood trees and therefore sandalwood forest were surveyed and symptomatic samples were collected from this area. The study confirmed the disease association with AY phytoplasmas and allow to verify the presence of a novel AY phytoplasma strains indicating that phytoplasma strains are differentiating with their plant host species and geographic regions.

Tamarind is an economically important tree species; its fruit pulp is widely used in kitchen in India. A symptomatic tamarind tree with yellow leaf symptoms found in the western part of India was assayed for phytoplasma presence. The 16S rDNA sequence of the detected phytoplasma (TM01) was found clustering with sequences in the elm yellows (16SrV) phytoplasma group. The virtual RFLP analysis of obtained 16S rDNA sequence TM01 revealed that it could be tentatively classified into a novel phytoplasma subgroup, 16SrV-L since its AluI, HaeIII and MseI restriction profiles of R16F2n/R16R2 sequenced amplicons generated were unique as compared to the earlier reported profiles of this phytoplasma subgroup. This is the first phytoplasma report in Tamarindus indica.

Phytoplasmas have been found associated with 129 plant species in India including vegetables, legumes, spices, medicinal plants and ornamental plants, cash and oil crops, palms, fruit trees and weeds, where ten 16Sr groups of phytoplasmas have been identified so far. Sesame phyllody, brinjal little leaf, sugarcane grassy shoot, sandal spike, coconut root wilt, areca nut yellow leaf and many diseases in ornamental plants are causing the most severe economic losses in the country. Identified phytoplasmas are related to ‘Candidatus Phytoplasma asteris’, ‘Ca. P. pruni’, ‘Ca. P. ziziphi’, ‘Ca. P. trifolii’, ‘Ca. P. solani’, ‘Ca. P. cynodontis’, ‘Ca. P. oryzae’, ‘Ca. P. phoenicium’, ‘Ca. P. australasia’ and ‘Ca. P. pini’. Among them ‘Ca. P. asteris’-related strains (aster yellows, 16SrI group) are the prevalent phytoplasmas identified associated with 62 diseases followed by phytoplasmas classified in 16SrII, 16SrVI, 16SrXIV and 16SrXI groups. At least seven insect vectors, belonging to leafhoppers and planthoppers species, have been reported as putative or natural vectors for important phytoplasma diseases. The majority of phytoplasma disease reports are from north and south part of India. Little attempt has been made to genomics, epidemiology, host phytoplasma interaction and management aspects of these diseases. Presently the suggested effective management practices in India are growing resistant varieties, control of insect vectors, weed species as alternative hosts and use of healthy planting materials.

Disease symptoms characterized by phyllody, yellowing of leaves, stunting, and virescence were observed in economically important fodder crops like alfalfa and “bajra” x napier grass hybrid grass. Similar symptoms were found in bell pepper or “shimlamirch”, a common vegetable grown all over India; “bajra” a significant widespread cereal crop in Maharashtra and Karnataka and in the nuisance weed Parthenium hysterophorus collected in the vicinity of above fodder growing fields. The successful amplification of specific 16S rRNA gene in all collected symptomatic plants confirmed the presence of phytoplasmas and their sequences analysis revealed their close relationship with strains of ‘ Candidatus Phytoplasma australasia’. Using EzTaxon, a microbial 16S rRNA sequence database, and i PhyClassifier- an online phytoplasma taxonomy tool, group 16SrII, subgroup D was identified for the classification of these sequences. This is the first report of 16SrII-D phytoplasmas associated with phyllody and yellowing diseases of “bajra” and bell pepper in India (PDF) First report of 16SrII-D phytoplasmas associated with fodder crops in India. Available from: https://www.researchgate.net/publication/322687543_First_report_of_16SrII-D_phytoplasmas_associated_with_fodder_crops_in_India [accessed Dec 24 2018].

The disease symptoms characterised by little leaf, phyllody, stunting and branch proliferation were observed during a field survey conducted from June 2015 to January 2016 on common invasive weeds Cleome viscosa (tick weed), Trichodesma zeylanicum (cattle bush) and Tephrosia perpurea (wild indigo), which were found infected with peanut witches’ broom phytoplasmas (16SrII group) strains. Phylogenetically similar phytoplasma strains were also detected in symptomatic samples of Sesamum indicum (sesame), Vigna unguiculata (cow pea), Phaseolus vulgaris (French bean), Dendrocalamus strictus (bamboo) and Carica papaya (papaya) from the same or adjacent fields. This is the first report of 16SrII-D group phytoplasmas (‘Candidatus Phytoplasma aurantifolia’-related strains) associated with witches’ broom disease of C. viscosa, D. strictus and yellow stunting disease of C. papaya. The association of 16SrII-C group phytoplasmas with witches’ broom disease of T. zeylanicum and T. purpurea is also reported for the first time. From the obtained results, it can be inferred that the weed hosts harbors 16SrII group phytoplasma strains associated with little leaf and witches’ broom diseases of economically important grain legume crop species like S. indicum, V. unguiculata and P. vulgaris.