Detection and molecular characterization of 'Candidatus Phytoplasma australasiaticum' in Aegle marmelos: a fruit of high medicinal values in India.

ABSTRACT

In surveys conducted from 2020 to 2022, five leaf samples each from symptomatic Agele marmelos trees and seedlings, along with five samples from asymptomatic trees and seedlings, were collected in Ayodhya, Uttar Pradesh, India. The DNA extraction from all the samples was subjected to nested PCR assays, using the universal phytoplasma-specific primers set (P1/P7 followed by R16F2n/R16R2). The resulting 1.2 kb amplified products were observed in all the symptomatic samples but not in the asymptomatic samples. Bael phytoplasma strain sequences from the trees and seedlings were found 100% identical within themselves and only two representative sequences (one each from tree and seedling) were deposited in GenBank (NCBI) as PP415872 (AmA-1) and PP415873 (AmA-2). BLASTn searches revealed the maximum (100%) sequence identity with a phytoplasma strain from murraya little leaf strain of Faizabad (GenBank Acc.no. OP984129) and lowest (99.84%) with arecanut crown choking of Shimoga (GenBank Acc. no. OM417502) from Karnataka. Phylogenetic analysis clustered the bael phytoplasma isolates with peanut witches' broom group phytoplasma strains. Virtual RFLP analysis confirmed their identity as 'Ca. P. australasiaticum', a 16SrII-D subgroup strain. This study presents the first identification of a phytoplasma strain in A. marmelos, emphasizing its potential threat to fruit crops and the need for vigilance in nursery practices to prevent further dissemination.