Phytoplasma diseases of coconuts: understanding their transmission and the sustanable breeding of resistant and tolerant varieties.

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Coconut is a vital crop in much of Africa as a source of food and income, but many palms are succumbing to Lethal Yellowing like (LYD) diseases caused by phytoplasmas. There is no effective remedial treatment for infected palms, so replanting with resistant or tolerant varieties is the best way to manage the disease. However, distribution of germplasm is being restricted because evidence suggests that phytoplasmas might be transmitted through seed and embryo cultures. This project will produce evidence on the risk of seed and embryo transmission, establish which palm varieties possess resistance / tolerance and whether environmental factors influence this, and develop molecular markers to track resistance / tolerance in breeding programmes. To investigate transmission we will produce embryo cultures from infected seed and use molecular diagnostics to determine whether LYD is present, and will plant seeds from infected palms to determine whether LYD is transmitted into progeny plants. Antibodies raised against the LYD SecA protein will be used to develop immunofluorescence microscopy techniques to localise phytoplasmas within infected embryos and inflorescences to show how the organisms might pass into seeds. To examine tolerance and resistance, qPCR or T-RFLP will be used to quantify the levels of LYD in a range of coconut cultivars in Ghana over a three year period. By monitoring specific palms and taking samples during dry and wet seasons, we will show which varieties are immune to disease and which contain phytoplasmas without showing symptoms (tolerance). Established SSR and AFLP markers, and markers that we develop based on resistance gene analogues, will be mapped onto the palms that we screen for LYD to identify markers that are useful for identifying resistant palms to distribute for replanting. At the same time an F2 mapping population will be established as part of a long term programme to map resistance / tolerance traits onto the coconut genetic map.