Pathosystem associated with phytoplasmas in forest plants is an emerging threat to forest productivity and biodiversity. Diseases caused by or associated with phytoplasmas occur in hundreds of commercial and native plants, causing minor to extensive damage. Phytoplasmas are wall-less, phloem-limited, insecttransmitted, plant pathogenic bacteria that are transmitted by phloem-sap feeding insects of the order Hemiptera under the families such as Cicadellidae, Delphacidae, Cixiidae, Derbidae, Psyllidae and rarely by Pentatomidae and Tingidae. Disease transmission occurs very quickly, often plants become infected before adopting any management strategies. The single most effective management practice of managing the vector in agricultural/horticultural crop is to cover plants with insect exclusion netting but this is not feasible and practical in the case of forest trees. Because of these limitations, researchers are shifting to manipulation genetics in host plants to affect vector populations and transmission of pathogen but big lacunae exists in our knowledge on the vectors of phytoplasma diseases in Indian forestry. We review the literature addressing the phytoplasma diseases in forest species, the lacunae existing in the insect vectors and the need for determining the vectors for possible management of phytoplasma diseases in forest trees.

The Sandalwood Spike disease (SSD)-related to ‘Ca. Phytoplasma asteris’ has threatened the existence of sandalwood in India. The epidemiology of SSD is still poorly understood despite the efforts to understand the involvement of insect vectors in SSD transmission and alternate plant hosts over the last two decades. Apart from the transmission of SSD phytoplasma through insect vectors, the information on vertical transmission is entirely unknown. Over 200 seeds from SSD-affected trees and over 500 seedlings generated using commercially purchased seeds were screened for the presence of SSD phytoplasma to understand the vertical transmission in an insect-free environment. The end-point nested PCR and real-time nested PCR-based screening revealed an alarming rate of 38.66% and 23.23% phytoplasma positivity in one-month and four-month-old seedlings, respectively. These results were further validated by visualizing the phytoplasma bodies in sandalwood tissues using scanning electron microscopy. The presence of phytoplasma DNA in the seeds and seedlings is a concern for the commercial distribution of sandalwood seedlings in the current setup. This also poses a fear of spreading the disease to newer areas and negatively affecting the economy. The seedling mortality was also suspected to be associated with isolated bacterial and fungal isolates such as Erwinia, Curtobacterium, Pseudomonas, Rhodococcus, Aspergillus, Fusarium, and Neofusicoccum isolated using a culture-dependent approach. These findings strongly recommend the accreditation of commercial production of sandalwood seedlings curtailing SSD phytoplasma’s menace. Additionally, a new nested end-point and qRT PCR assays developed in this study proved valuable for the rapid screening of phytoplasma in many plant samples to detect phytoplasmas.

A novel, ‘mustard yellow’ pigmented aerobic bacterial strain designated AR01T was isolated from hypocotyl tissue of a sandalwood seedling from Bangalore, India. The 16S rRNA gene of strain AR01T had the highest 98.97% sequence similarity with Rothia halotolerans YIM 90716T (KCTC 19172) followed by Rothia kristinae PM 129T (NBRC 15354T) (97.31%) and Rothia koreensis P31T (JCM 15915) (97.11%), respectively. The strain AR01T was coccoid-shaped, non-motile, non-spore-forming, oxidase-negative, and catalase-positive. The strain AR01T has a genome size of 3.31 Mb containing 2993 protein-coding genes including 48 tRNA and 10 rRNAs spread across 84 contigs. The genomic DNA G + C content was 71.77 mol%. The calculated dDDH was 31.10%, and the OrthoANI value was 85.27% compared to its closest related type strain Rothia halotolerans YIM 90716T. The predominant cellular fatty acids were C16:0 iso (30.04%), C15:0 anteiso (37.42%), and C17:0 anteiso (21.78%). The strain AR01T contains major polar lipids including diphosphatidylglycerol and phosphatidylglycerol. Based on the distinct physiological, biochemical characteristics and genotypic relatedness indicated that AR01T represents a novel species of the genus Rothia, for which the name Rothia santali sp. nov. (Type strain AR01T = MCC 4800T = JCM 35593T) is proposed.The GenBank/EMBL/DDBJ accession number for the reference 16S rRNA gene sequences of the strain AR01T is OM838448. The accession number of the whole-genome of AR01T is JANAFB000000000

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