New Efficient Natural Leafhopper Vectors of Sugarcane Grassy Shoot Phytoplasma in India

Abstract

Sugarcane grassy shoot (SCGS) disease is associated with the presence of 16SrXI group phytoplasmas that are transmitted by leafhoppers; limited studies have been performed in India toward its natural transmission. To determine the insect vectors that transmit the disease in nature, leafhopper species from SCGS-infected fields at Shahjahanpur, Central Uttar Pradesh, India, were collected and analyzed for phytoplasma presence using nested polymerase chain reaction with phytoplasma-specific primers. An ~1.2-kb amplified DNA fragment was detected in nested PCR from the three major leafhopper species, viz. Maiestas portica (Melichar), Exitianus indicus (Ross) and Cofana unimaculata (Signoret), and the symptomatic sugarcane leaves of variety CoS 07250. BLASTn analysis of ~1.2-kb 16S rDNA partial sequences obtained from symptomatic sugarcane plants and these leafhoppers revealed 99–100 % sequence identities among themselves and 99 % identity with other reported strains of ‘Candidatus Phytoplasma oryzae’ (16SrXI group). Phylogenetic analysis of 16S rRNA sequences of SCGS, M. portica, C. unimaculata and E. indicus phytoplasma strains also indicated the closest phylogenetic relationship with those of ‘Ca. P. oryzae’ group. Transmission tests and population sampling study further confirmed that M. portica and C. unimaculata were vectors of the SCGS phytoplasma from diseased to healthy sugarcane plants. The identification of new vectors of SCGS phytoplasma suggested that these leafhopper species may be responsible for secondary spread of SCGS phytoplasma.