Advances in sesame phyllody disease: Etiology, vector transmission, epidemiology, diagnosis and integrated management

Vollständiger Abstract

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Sesame (Sesamum indicum L.) is an important oilseed crop whose productivity is significantly reduced by phyllody disease. Phytoplasmas present in the phloem tissue of the plant cause sesame witches'-broom disease. The abnormal development of a floral organ into a leaf-like structure (phyllody) and the development into green pigmentation in floral parts (virescence), resulting in sterility and reduced seed production. This disease is common in Africa and Asia and parts of Europe. Infection is mainly through insect vectors, especially the leafhoppers (Orosius albicinctus). Phyllody disease-associated phytoplasmas are of diverse ribosomal groups, with the 16SrII group associated with peanut witches'-broom highly prevalent. A fast and accurate diagnosis can be achieved using molecular diagnostics such as polymerase chain reaction (PCR). Phyllody negatively impacts many important agronomic traits of sesame, like plant height, number of capsules per plant and 1000 seed weight. Control of the disease involves some cultural practices (removal of symptomatic plants, use of certified disease-free seeds and change in planting date to avoid peak vector activity); limited chemical control by insecticides aimed only at the vector; and biological practices to improve the efficacy of natural vector antagonists. It seems that it is possible to develop sesame genotypes that are resistant or tolerant to phyllody, making it a sustainable management strategy. Yet, the polygenic nature of phyllody and the complicated nature of the resistance mechanisms have been an impediment. Further studies would be required to understand the ecology of the vectors and phytoplasma-host interaction and to facilitate the development of sesame varieties that have resistance or tolerance to disease. This review summarises current knowledge on the origin, transmission, epidemiology, symptomatology, diagnostics and management of sesame phyllody disease.