RESUMO
Symptoms typical of phytoplasma infection such as phyllody, virescence, witches' broom and yellowing were observed in 12 varieties of Chrysanthemum morifolium in floral nurseries and experimental fields at New Delhi, Karnataka, Maharashtra and Andhra Pradesh, India, during surveys made from 2015 to 2017. Disease incidence ranged from 15 to 30%. Phytoplasma presence was confirmed in all symptomatic chrysanthemum varieties by molecular identification assays. Sequence comparison, phylogenetic and in silico RFLP analyses of 16S rDNA sequences allowed the identification of the chrysanthemum infecting phytoplasma strains into different ribosomal groups and subgroups, namely 16SrI, 16SrII-D, 16SrVI-D and 16SrXIV. Detection of phytoplasma strains of 16SrII-D subgroup were also confirmed in symptomatic Chenopodium album and Parthenium hysterophorus plants grown in and around the surveyed chrysanthemum fields at New Delhi, whereas 16SrVI-D phytoplasma strains were detected in symptomatic Cannabis sativa weed and leafhopper Hishimonus phycitis individuals collected from the symptomatic chrysanthemum fields at New Delhi. This is the first report on the presence of 16SrVI and 16SrXIV groups of phytoplasmas in chrysanthemum plants. Studies on genetic diversity of phytoplasmas infecting the major chrysanthemum varieties in India and their epidemiological aspects had previously not been reported. The detection and identification of phytoplasmas in different chrysanthemum varieties could contribute to increase the awareness among farmers in the management of these diseases.
RESUMO
Suspected phytoplasma symptoms of little leaf, yellowing, chlorosis, phyllody, witches' broom, and stunting were observed on ten different ornamental plant species at New Delhi, Andhra Pradesh, Haryana, Bengaluru, and Pune, India, during March to July 2016. To investigate the possibility of phytoplasma etiology, PCR assays were performed using universal primer pairs (P1/P7 followed by 3Far/3Rev) specific to the phytoplasma 16Sr RNA gene. First round PCR amplification with primer pair P1/P7 did not yield expected 1.8 kb product of 16S rRNA region from any of the 17 symptomatic samples. However, 1.3 Kb amplicons were observed in nested PCR assays with 3Far/3Rev primer pair in symptomatic leaf samples of Hibiscus rosa-sinensis L. (Pune isolate), Saponaria officinalis L. (Pune isolate), and Allamanda cathartica L. (Delhi isolate). No amplifications were observed in any of the other tested symptomatic and non-symptomatic plant samples either in first round or second round of nested PCR assays with phytoplasma specific primer pairs. Pairwise sequence comparison of 16S rDNA sequences of the five positive phytoplasma strains of A. catharica, H. rosa-sinensis, and S. officinalis in the present study revealed 99-100% sequence identities with strains of 'clover proliferation' (16SrVI) group. Phylogenetic and virtual RFLP analysis of 16S rDNA sequences of the five identified phytoplasma strains belonging to three ornamental species further confirmed their clustering and grouping with member strains of 'clover proliferation' subgroup D. This is the first record of the phytoplasma association of 'clover proliferation' subgroup D with H. rosa-sinensis, S. officinalis, and A. cathartica in the world.
