Multilocus sequence analysis of a 'Candidatus Phytoplasma Australasia'-related strain associated with peanut little leaf disease in India.
Severe little leaf and excessive shoot proliferation symptoms typical of the peanut little leaf (PnLL) disease were observed in different peanut (Arachis hypogaea) fields, variety K-6, at Kadiriand Gooty regions, of Andhra Pradesh, India, during the monsoon season of 2018-19. Disease incidence was 2-3%. The phytoplasma etiology of the recorded disease was confirmed by amplifying ~1.25 kb DNA products of 16S rRNA gene from symptomatic plants using nested polymerase chain reaction with phytoplasma specific primers, P1/P7 and R16F2n/R16R2, respectively. A further confirmation of the phytoplasma etiology was obtained by amplification of 840 bp, 1094 bp and 465 bp DNA fragments using phytoplasma specific primers targeting secA, tuf and SAP11 genes, respectively. Sequence and phylogenetic analyses of the amplified 16S rRNA, secA, tuf and SAP11 genes revealed that the detected phytoplasma is a member of the peanut witches'-broom phytoplasma group or 16SrII group ('Candidatus Phytoplasma australasia'). Also, on the basis of computer-simulated RFLP (= in silico RFLP) analysis of amplified 16S rRNA gene, the detected phytoplasma was assigned to subgroup D (16SrII-D). Parthenium hysterophorus plants showing witches' broom and Cleome viscosa plants with little leaf symptoms, both collected in the mentioned peanut fields were also infected by similar strain of phytoplasma which proved to be identical with each of the molecular marker employed to the peanut-infecting agent in India. This is the first report on the association of 'Ca. P. australasia' (16SrII-D subgroup phytoplasma) with PnLL disease in India.