STUDIES ON MOLECULAR RELATIONSHIP OF PHYTOPLASMAS ASSOCIATED WITH SELECTED WEED HOSTS AND CROP PLANTS

Diseases caused by phytoplasmas are gaining importance in recent years on pigeonpea, chickpea, buckwheat, sunhemp, sesamum, brinjal and parthenium. Survey carried out in Southern Karnataka, revealed the incidence of phytoplasma in pigeonpea, brinjal, sesamum, chickpea, sunhemp and parthenium which ranged from 0.10 to 7.42 per cent (2018-19) and 0.12 to 6.90 per cent (2019-20). Sesamum phyllody successfully transmitted by leafhoppers (H. phycitis) with 48 h of AAP and IAP and 30 days of incubation period. Ten H. Phycitis sufficient to cause 100 % transmission. Sesamum phyllody was successfully transmitted to parthenium. Molecular characterization was carried out through PCR using phytoplasmal specific primer pairs P1/P7, R16F2n/R16R2, TUF-II-F2/TUF-II-R2 and SecA-II-F2/SecA-II-R2 which yielded expected amplicon of 1.8 kb, 1.2 kb, 1 kb and 1.2 kb, respectively. Based on phylogenetic analysis of 16S rDNA, tuf and SecA revealed that Datura stramonium, pigeonpea, chickpea, sunhemp, buckwheat, brinjal, sesamum and parthenium phytoplasma belongs to 16SrII phytoplasma group. Increased activity of total phenols and peroxidase in phytoplasma infected leaves of brinjal, sesamum, pigeonpea and chickpea was observed. Decreased catalase activity was observed in phytoplasma infected leaves of brinjal, pigeonpea and chickpea except sesamum. Increased PAL activity was observed in phytoplasma infected leaves of sesamum, chickpea and pigeonpea except brinjal. Seven endosymbiotic bacteria from H. phycitis showed negative reaction to Indole and Voges-Proskauer test (EBHP-1 to 7). In citrate, except EBHP-5 remaining showed positive reaction. Further, in the methyl red EBHP-2, 5, 6 and 7 showed positive and remaining three showed negative (EBHP-1, 3 and 4). PCR assay of DNA extracted from endosymbionts using primer Fp1/Rp2 revealed the amplification of 1.4 kb fragment corresponding to 16S rRNA. Phylogenetic analysis revealed EBHP-1, 3, 6 and 7 closely clustered with Pseudomonas sp, EBHP 4 and 2 with Exiguobacterium sp. and EBHP-5 with Achromobacter sp.