Tri-Trophic Relationship among Sugarcane White Leaf Disease Phytoplasma (WLDP), <em>Deltocephalus menoni</em> (Homoptera: Cicadellidae) and Sugarcane Plant in Secondary Transmission of the Disease

Abstract

Purpose: Sugarcane White Leaf Disease (WLD) is one of the most devastative diseases in cane-sugar industry in Sri Lanka and the causative agent is a distinct phytoplasma (WLDP) strain within the 16SrXI. White Leaf Disease spreads through infected seed cane and insect vector; Deltocephalus menoni (Hemiptera: Cicadellidae). This paper presents the tri-trophic relationship of the plant, vector and pathogen in disease transmission. Research Method: Four-month-old sugarcane plants of the variety SL 96 128 and laboratory-reared populations of D. menoni were used for this study. Performance of D. menoni on healthy plants and WLD plants was examined in relation to the aggregation, amount of feeding, fecundity, number of nymphs emerged, nymphal period, survival of nymph and adult’s longevity. The plant architecture, leaf histological and physiological aspects were also studied. Findings: Except for nymphal period, all behavioural characteristics were significantly-high in WLDinfected plants in 10, 14, 30, 8, 12 and 17 percent, respectively. The nymphal period of D. menoni was significantly-reduced by 12.78 percent. Number of shoots (41.83 percent) and leaves (18.96 percent) were high and distance between two leaves tends to be reduced by 32.85 percent in diseased-plants altering plant architecture into a profuse and bushy nature. Sucking distance, thicknesses of lower epidermis and phloem fibre layer in leaves were significantly reduced in infected plants. Leaf N, P, K and moisture content increased (24.89, 34.78, 28.64 and 3.85percent) while leaf wax content was reduced by 4.93 percent. Originality/value: Disease infected plants are augmenting its vector; D. menoni by attracting, enhancing survival and population build-up which promotes the transmission of WLD phytoplasma itself. There by regular inspection and rogueing out of WLD infected clumps make a great impact on secondary transmission of WLD by D. menoni.