Sesame phyllody disease: its symptomatology, etiology, and transmission in Pakistan

Phyllody is a serious disease of sesame in Pakistan. In the present study investigations were carried out on the symptomatology, etiology, and transmission of this disease. Floral virescence, phyllody, and proliferation are the most common symptoms. Sometimes these symptoms are accompanied by yellowing, cracking of seed capsules, germination of seeds in capsules, and formation of dark exudates on the foliage. Shoot apex fasciation has also been occasionally observed, but no phytoplasma DNA has been detected in fasciated plants using PCR assays. Light microscopy of hand-cut sections treated with Dienes' stain showed blue areas in the phloem region of phyllody-infected plants. Pleomorphic bodies (phytoplasma structures) were observed in phloem sieve elements in diseased plants using transmission electron microscopy (TEM). Amplification of a phytoplasma characteristic 1250-bp 16S rDNA fragment confirmed that sesame was infected by a phytoplasma, and RFLP profiling and sequencing confirmed that the associated phytoplasma had the greatest homology to 16SrII-D group phytoplasmas. Phyllody disease was successfully transmitted by grafting dodder (Cuscuta compestris) and leafhopper (Orosius albicinctus). Treatment of infected plants with tetracycline-HCl provided temporary recovery from the disease.