The CSPWD is the Ghanaian form of lethal yellowing disease (LYD) of coconut, caused by a phytoplasma and has been active in Ghana since 1932. The paper updates the results of screening trials conducted with 38 pure and hybrid coconut varieties since 1981. Although no variety was found totally resistant, a wide range of susceptibility level was observed: almost all SGD were still unaffected, while the local WAT had almost totally disappeared, additive values were calculated for the parental varieties and it was shown that, in the average, hybrids are slightly more susceptible than predicted by a purely additive model. According to this genetic model, the SGD 9 VTT hybrid will be appreciably less susceptible than the MYD 9 VTT currently being used for replanting devastated farms in Ghana. Our results tend to confirm the general trend that cultivars from the Pacific group (especially the Dwarfs) are less susceptible than the Indo-Atlantic cultivars. Proposals are made to adapt planting material to the risk level. Genetic control can only be efficient if it is considered as a link in a chain of control measures involving the choice of a proper planting site, good management and early eradication of diseased trees.

Coconut palms (Cocos nucifera L.) can be affected by several types of Lethal Yellowing (LY) diseases worldwide. Some of the syndromes are caused by phytoplasmas, small bacteria that are impossible to detect by light microscopy. Amplification of a given gene of the phytoplasmas by polymerase chain reaction (PCR) is the most convenient diagnosis method. The problem is that there are at least 28 "groups" of phytoplasmas and only one pair of primers-P1/P7-commonly used for PCR. As these primers belong to a very conserved gene, false positives are frequent. Consequently, alternative primers specific to one "strain" (or subgroup) have to be used, such as LY-F/LY-R for the Caribbean LY, Rohde primers for LD Tanzania. Such specific primers are sometimes restrictive. Indeed, there is variability within each strain and the sequence of the primers has to be adapted to that variability. There are at least five LY subgroups. The subgroups can only be identified by restriction fragment length polymorphism or sequencing. In Africa, two subgroups of LY phytoplasmas have been identified so far.

The Cape Saint Paul Wilt Disease (CSPWD), a lethal-yellowing type disease of coconut has been in Ghana since 1932. Aerial and/or ground surveys were undertaken to assess the current status of the disease spread. The survey showed that the spread of the disease for the past 5 years has mainly been the expansion of existing foci. However, new outbreaks were identified at Glidzi in the Volta, Bawjiase and Efutu Breman in Central regions. After the resurgence in the Volta region in 1995, the Woe-Tegbi-Dzelukope corridor has remained endemic, but less aggressive. Pockets of healthy groves remain along all the coastline and inland of known disease zones. Eradication of diseased palms at Ampain focus lying just about 60 km to the Ivorian border, and disease situations on new replanting with MYD × VTT hybrid are discussed.

The Lethal Yellowing (LY) disease is one of the main threats to coconut industry in many parts of Africa and the Caribbean. Planting resistant varieties has long been recognized as one of the most promising ways of controlling the disease. Considerable efforts have been devoted throughout the world to screening suitable varieties and have often involved international cooperation. It has proven to be a lengthy and difficult task. We present an overview of these efforts with special mention to Ghana, Jamaica and Mexico. Although no variety so far has been proven fully and permanently resistant, treating resistance level as a threshold trait makes it possible to demonstrate significant differences among varieties, which can be exploited effectively to make genetic improvement a component of an integrated control strategy. Based on past experience, we make a few suggestions to increase the diversity of resistance sources and increase the level and the sustainability of resistance to LY in coconut.

To sustain epidemiological studies on coconut lethal yellowing disease (CLYD), a devastating disease in Africa caused by a phytoplasma, we developed a multilocus sequence typing (MLST) scheme for “CandidatusPhytoplasma palmicola” based on eight housekeeping genes. At the continental level, eight different sequence types were identified among 132 “CandidatusPhytoplasma palmicola”-infected coconuts collected in Ghana, Nigeria, and Mozambique, where CLYD epidemics are still very active. “CandidatusPhytoplasma palmicola” appeared to be a bacterium that is subject to strong bottlenecks, reducing the fixation of positively selected beneficial mutations into the bacterial population. This phenomenon, as well as a limited plant host range, might explain the observed country-specific distribution of the eight haplotypes. As an alternative means to increase fitness, bacteria can also undergo genetic exchange; however, no evidence for such recombination events was found for “CandidatusPhytoplasma palmicola.” The implications for CLYD epidemiology and prophylactic control are discussed. The usefulness of seven housekeeping genes to investigate the genetic diversity in the genus “CandidatusPhytoplasma” is underlined.IMPORTANCECoconut is an important crop for both industry and small stakeholders in many intertropical countries. Phytoplasma-associated lethal yellowing-like diseases have become one of the major pests that limit coconut cultivation as they have emerged in different parts of the world. We developed a multilocus sequence typing scheme (MLST) for tracking epidemics of “Ca. Phytoplasma palmicola,” which is responsible for coconut lethal yellowing disease (CLYD) on the African continent. MLST analysis applied to diseased coconut samples collected in western and eastern African countries also showed the existence of three distinct populations of “Ca. Phytoplasma palmicola” with low intrapopulation diversity. The reasons for the observed strong geographic patterns remain to be established but could result from the lethality of CLYD and the dominance of short-distance insect-mediated transmission.