ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 67 Number 1
Transmission of root (wilt) disease to coconut seedlings through Stephanitis typica (Distant) (Heteroptera:Tingidae)
Two-year-old West Coast Tall coconut seedlings obtained from a disease-free area were planted in methyl bromide-fumigated loamy sand collected from paddy field, held in field tanks and protected inside netted field cages. The seedlings were regularly inoculated with infective lace bugs, Stephanitis typica. Spear-leaf tissues of three of the four experimental seedlings gave strong positive serological reactions, indicating infection, nine months after the first inoculation. Root tissues treated with Dienes's stain, DAPI and Hoechst 33258 fluorochromes indicated mycoplasma-like organisms (MLO) infection in the phloem. Serological and stain reactions in the fourth seedling were feeble at that time. Electron microscope examination of ultra thin sections of root apexes of all the seedlings revealed the presence of mycoplasma-like organisms in the sieve tubes. Of the four seedlings to which MLOs were transmitted by the tingids, two developed flaccidity of leaflets, the diagnostic and decisive symptom of the disease, eight months after infection was indicated by serodiagnosis. By the time the seedlings were visually identified as manifesting the symptom of the disease, each seedling had received more than 1000 lace bugs with five days' acquisition feeding on diseased palms known to harbour MLOs and about 1130 lace bugs with five days' acquisition and thirteen days' incubation. Control plants remained free of the organism and the symptoms of the disease.
Keywords: Coconut root wilt; MLO; Lace bug vector; Stephanitis typica; Fluorescence; Electron microscopy