Advances in the research of the two most important diseases on oil palm in Colombia: bud rot and lethal wilt

The two most important diseases on oil palm in Colombia are bud rot and lethal wilt. The first one, caused by Phytophthora palmivora has destroyed several plantations since 1964 when the first cases were registered and lately wiped out more than 30.000 hectares on South-West Colombia and more than 10.000 in the Central Zone. Lethal wilt caused the destruction of more than 2000 hectares in Oleaginosas Risaralda in the decade 1965-1975, and since 1994 near one thousand hectares in Bajo Upia in the East Zone. Bud rot infection takes place in the very young tissue of immature spear leaves and the lesions are observed a few days later, when the affected tissues are exposed to the outside environment. It is present in all stages of development of the palms, since the nursery until the end of its production cycle. Lethal wilt is only observed once the palms reach their bearing stage. In this case there are evidences that a sucking insect is involved in the dissemination process of the causal agent of the disease and that grasses growing below the oil palms are playing an important role in the development of the epidemics, because they are hosts for the immature stages of the insect. In this study we are presenting the recent advances in the research with these two diseases. With bud rot it was possible to use an in vitro test, using very young leaflets, to identify the differences in susceptibility in several stages of development, to establish the time for development of the first symptoms, to observe the infection process under the microscope, to determine the production of structures and differences in susceptibility to infection in several materials or on leaflets collected from palms with different chemical treatments, confirming the role of Phytophthora palmivora in the production of the disease and developing a promising procedure for screening of resistant materials and molecules for the control of this pathogen. With lethal wilt the Cixiidae Myndus crudus van Duzee, was selected for transmission tests because its antecedents as vector of diseases in oil and coconut palms. The results indicated that it was possible to transmit the causal agent of lethal wilt, with an average feeding acquisition time of 2. 7 days, an average incubation time in the insect for 5.5 days and an average inoculation time of 2.6 days. There was 21% of transmission with insects exposed to disease palms and 6% in the controls. The latter cases of transmission can be explained by the experimental conditions used. There was an incubation period of the pathogen in the palms of 167 days. These results confirmed the role of Myndus crudus in the transmission of the causal agent of lethal wilt in Colombia and it gives new opportunities to proceed with the identification of the disease causal agent.