Molecular characterization of phytoplasma associated with four important ornamental plant species in India and identification of natural potential spread sources

Genetic diversity of phytoplasma strains infecting chrysanthemum varieties in India and their possible natural reservoirs

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.

Pest categorisation of the non-EU phytoplasmas of Cydonia Mill., Fragaria L., Malus Mill., Prunus L., Pyrus L., Ribes L., Rubus L. and Vitis L

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of nine phytoplasmas of Cydonia Mill., Fragaria L., Malus Mill., Prunus L., Pyrus L., Ribes L., Rubus L. and Vitis L. (hereafter “host plants”) known to occur only outside the EU or having a limited presence in the EU. This opinion covers the (i) reference strains of ‘Candidatus Phytoplasma australiense’, ‘Ca. P. fraxini’, ‘Ca. P. hispanicum’, ‘Ca. P. trifolii’, ‘Ca. P. ziziphi’, (ii) related strains infecting the host plants of ‘Ca. P. aurantifolia’, ‘Ca. P. pruni’, and ‘Ca. P. pyri’, and (iii) an unclassified phytoplasma causing Buckland valley grapevine yellows. Phytoplasmas can be detected by available methods and are efficiently transmitted by vegetative propagation, with plants for planting acting as a major entry pathway and a long‐distance spread mechanism. Phytoplasmas are also transmitted in a persistent and propagative manner by some insect families of the Fulgoromorpha, Cicadomorpha and Sternorrhyncha (order Hemiptera). No transovarial, pollen or seed transmission has been reported. The natural host range of the categorised phytoplasmas varies from one to more than 90 plant species, thus increasing the possible entry pathways. The host plants are widely cultivated in the EU. All the categorised phytoplasmas can enter and spread through the trade of host plants for planting, and by vectors. Establishment of these phytoplasmas is not expected to be limited by EU environmental conditions. The introduction of these phytoplasmas in the EU would have an economic impact. There are measures to reduce the risk of entry, establishment, spread and impact. Uncertainties result from limited information on distribution, biology and epidemiology. All the phytoplasmas categorised here meet the criteria evaluated by EFSA to qualify as potential Union quarantine pests, and they do not qualify as potential regulated non‐quarantine pests, because they are non‐EU phytoplasmas.

DNA barcoding and phylogenetic analysis of leafhoppers associated with Aster Yellow disease on China aster, Marigold and Chrysanthemum

The Cicadellidae (Auchenorrhyncha: Hemiptera) are important agricultural, horticultural and ornamental pests. But it is very difficult to define nymphs and female adults using morphological characteristics. This research was aimed at understanding the variety of leafhoppers species and defining the prospective cause of the aster-yellow disease in China Aster, Marigold and Chrysanthemum. Two surveys were conducted in and around Pune, Maharashtra and Bengaluru, Karnataka between November 2016 and February 2017. The mitochondrial cytochrome oxidase subunit I (mtCOI) region marker was used in the species diagnosis and genetic diversity research. Through the use of mtCOI molecular marker eight different leafhoppers species were identified as Sogatella furcifera, Homalodisca insolita, Amrasca biguttula, Balclutha incise and Balclutha abdominalis and Japanagallia trifurcate. Whereas at genus level identified as Toya, Empoasca, Perkinsiella, Hishimonus, Tambocerus, Phaconeura, Curena, Psammotettix and Graphocophala species. These results are strongly corroborated with morphological identification. On the basis of multiple sequence alignment of the mtCOI gene, a species phylogenetic tree with the highest likelihood was drawn. All the leafhopper species clustered together in accordance with the species data collected from the database of the different geographic regions from the NCBI GenBank and Barcode of Life (BOLD). Such results suggest that it is important to use both molecular and morphological methods to ensure accurate identification of organisms. To conclude, this research contributes valuable knowledge to molecular biology and recognizes leafhopper species that serve as major phytoplasma vectors.