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Genetic Variability of <i>Haplaxius crudus</i>, Based on the 5′ Region of the Cytochrome <i>c</i> Oxidase Subunit I Gene, Sheds Light on Epidemiology of Palm Lethal Decline Phytoplasmas

Haplaxius crudus is an economically important species of cixiid planthopper that is widespread and abundant throughout the Caribbean basin. It is the vector of lethal yellowing and putative vector of lethal bronzing, both phytoplasma diseases of palm that cause death in Florida and the Caribbean. The primary objective of this study was to evaluate the genetic diversity of H. crudus in Florida to determine whether divergent populations existed. The 5′ region of the cytochrome c oxidase subunit I gene was used as the molecular marker. DNA sequences were obtained from 236 specimens collected throughout Florida, United States as well as populations from the southeastern United States. Populations from Costa Rica, Colombia, and Jamaica were included to compare differences between isolated populations. In Florida, four haplotypes were discovered, with 97% of individuals belonging to a single haplotype, two smaller haplotypes comprising six and four individuals, and a single haplotype comprising one individual. Populations from Texas and Mississippi represented distinct haplotypes whereas populations from Georgia and South Carolina were identical to the predominant haplotype in Florida. Populations from Costa Rica and Colombia were highly divergent whereas the population from Jamaica was 100% identical to the predominant population in Florida. These findings highlight measurable levels of genetic variability of H. crudus in Florida, and the similarity to populations from Jamaica highlight the need for more robust sampling throughout the Caribbean to better understand movement and invasion potential of this species. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

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Identification of \u2018Candidatus Phytoplasma\u2019 species in \u201chuanglongbing\u201d infected citrus orchards in the Caribbean

“Huanglongbing” (HLB) is one of the most devastating diseases of citrus orchards worldwide. Samples from 183 citrus plants of different cultivars and rootstock/cultivar combinations, showing HLB symptoms in three Caribbean countries (Cuba, Jamaica, and Guadeloupe-France), were collected to verify the possible co-infection of ‘Candidatus Phytoplasma’ and ‘Candidatus Liberibacter’ species. The 64% of the samples resulted positive to the ‘Ca. L. asiaticus’ and the 27% to diverse ‘Ca. Phytoplasma’-related species, moreover about the 14% of the samples infected with ‘Ca. Liberibacter’ were also found positive to phytoplasmas, indicating the presence of mixed infection especially in the orchards located in Cuba. Moreover, in one of the samples from Jamaica mixed phytoplasma infection was detected. Moreover the detection of only phytoplasmas in 11 symptomatic citrus samples collected from Cuba and Guadeloupe without ‘Ca. Liberibacter’ detection, confirmed that the symptomatology cannot be the sole criterium to discriminate between the presence of the two pathogens, and molecular detection is necessary to identify single or mixed infections. Diaphorina citri insects collected from Cuba and Guadeloupe resulted infected with ‘Ca. L. asiaticus’ confirming its active role in the dissemination of the pathogen. Only one insect of the Cicadidae family, collected in Guadeloupe, was found positive for phytoplasma presence. Considering that the phytoplasmas belonging to some ‘Candidatus species’ were detected in the three countries in different citrus varieties, a relevant role as phytoplasma reservoir can be attribute to citrus orchards.

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Dealing with Lethal Yellowing and Related Diseases in Coconut

The coconut is a palm of economic and social importance; it is cultivated in 90 countries around the world and the markets of some of its products have been growing exponentially, representing a very promising future for the coconut cultivation and industry. Unfortunately, this is threatened by decreased fruit production due to ageing palms and lethal yellowing (LY) and related phytoplasma diseases (LYDs) that have been devastating coconut palms, particularly in countries of Latin America and the Caribbean (LAC), and Africa, although such diseases are also present in countries in Asia and Oceania. Much research has been carried out to understand LY and LYDs, and associated phytoplasmas have been identified. There are about 16 different strains within nine 16Sr phytoplasma groups. The more diverse group so far is the 16SrIV group, present in countries in the Americas, but also reported in Asia and Oceania. A search of vectors has resulted in one confirmed case in the Americas, a leafhopper (Haplaxius crudus Van Duzee, 1907), and other candidates have been identified but yet to be confirmed. Fifty palm species (including coconut) and 14 non-palm species have been reported as phytoplasma hosts. Screening for resistance has identified resistant germplasm in the Americas which has been used for replanting programs, and similar efforts are being conducted in other parts of the world. Methods for detection and diagnosis have been developed using PCR techniques. Micropropagation has been developed for massive propagation of the selected coconut germplasm. Management practices based on the above are currently being applied. However, even with all the progress achieved, there is still a lot to be done in order to move forward in how to deal more effectively with LY and LYDs. For this purpose, it is very important that research is carried out based on a global strategy, working worldwide in an organized and coordinated fashion, in collaboration with organizations such as ICC and COGENT.

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Floral Odors and the Interaction between Pollinating Ceratopogonid Midges and Cacao

Most plant species depend upon insect pollination services, including many cash and subsistence crops. Plants compete to attract those insects using visual cues and floral odor which pollinators associate with a reward. The cacao tree, Theobroma cacao, has a highly specialized floral morphology permitting pollination primarily by Ceratopogonid midges. However, these insects do not depend upon cacao flowers for their life cycle, and can use other sugar sources. To understand how floral cues mediate pollination in cacao we developed a method for rearing Ceratopogonidae through several complete lifecycles to provide material for bioassays. We carried out collection and analysis of cacao floral volatiles, and identified a bouquet made up exclusively of saturated and unsaturated, straight-chain hydrocarbons, which is unusual among floral odors. The most abundant components were tridecane, pentadecane, (Z)-7-pentadecene and (Z)-8-heptadecene with a heptadecadiene and heptadecatriene as minor components. We presented adult midges, Forcipomyia sp. (subgen. Forcipomyia), Culicoides paraensis and Dasyhelea borgmeieri, with natural and synthetic cacao flower odors in choice assays. Midges showed weak attraction to the complete natural floral odor in the assay, with no significant evidence of interspecific differences. This suggests that cacao floral volatiles play a role in pollinator behavior. Midges were not attracted to a synthetic blend of the above four major components of cacao flower odor, indicating that a more complete blend is required for attraction. Our findings indicate that cacao pollination is likely facilitated by the volatile blend released by flowers, and that the system involves a generalized odor response common to different species of Ceratopogonidae.

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