Investigaions into the phylogeography and ecology of Myndus crudus (van Duzee) (Hemiptera, Fulgoromorpha, Cixiidae), the leafhopper vector of coconut lethal yellowing
Lethal yellowing (LY) is caused by a phytoplasma which affects over 35 palm species, it is the most devastating disease of coconuts in the Caribbean and Americas. Dying palms with LY-like symptoms have been reported from the Caribbean for over 100 years. Epidemics destroyed millions of coconut palms in Jamaica and southern Florida in the 1960s and 1970s before LY spread from the Caribbean Islands to Yucatan, Mexico, in 1979 and more recently (1997) into Belize and Honduras. Phytoplasmas, Mollicute plant pathogens are transmitted by leafhoppers, planthoppers, and psyllids (Kirkpatrick, 1992). The planthopper Myndus crudus is the only accepted vector of LY, although few experimental transmissions have been documented (Howard and Wilson, 2001). Control of LY has been based on resistant varieties, especially the 'MayPan', a 'Malayan Dwarf x 'Panama Tall' hybrid, which has been planted extensively in Jamaica and Florida since the 1970s. Beginning in 1995, 'MayPans' in Jamaica succumbed to LY for the first time, and the epidemic has now reached crisis levels with damage far greater than that seen in the epidemics of the 1960's. In common with other phytoplasmas the LY phytoplasma remains uncultured but molecular studies have determined that it exists as a group of near identical strains in the western Caribbean region, belonging to the 16SrIV group of phytoplasmas. Little is known about phytoplasma-vector specificity or about prospective intraspecific diversity for the LY vector, M. crudus. Information regarding dispersal patterns of M. crudus, whether it is capable of flight locally or regionally is also lacking. Although severe LY outbreaks and its rapid jump spread are well documented, the mechanisms of longer distance spread are unknown although anecdotally, such outbreaks have been associated with the aftermath of severe weather events in the region, the last episode being Hurricane Mitch in 1998. Information is lacking concerning the diversity and distribution of M. crudus populations in the Americas, which are essential to our understanding of the ecology of this important pathogen-vector complex. Using PCR and degenerate primers we have undertaken a preliminary examination of the mitochondria. (mt) cytochrome oxidase gene for specimens of M. crudus collected in LY-free areas and in those where LY is active, in the Caribbean and in Mesoamerica. Degenerate PCR primers (Simon et al. 1994) were used to PCR amplify an 850 base pair (bp) fragment of the mt COI gene (Frohlich el al. 1999). from purified DNA extracts of leafhoppers. Amplicons were cloned, the nucleotide sequence determined in both sense and complementary directions and used to reconstruct a contig having a minimum of 250-300 bp overlap (Brown, 2000). Phylogenetic analysis (NIL, parsimony) was done to estimate genetic relatedness for M. crudus samples from Florida, Honduras, and individuals from a colony that was established in Jamaica in 1973 by P. Markham and has been maintained thereafter in an insectary in the UK. M. adiopodoumeensis from Ghana and Circulifer tennellus (Baker), the beet leafhopper from North America were included as outgroup species and genus, respectively. Preliminary results suggest the mt COI gene is an informative molecular marker with which to examine more extensively the intraspecific variation of M. crudus vector populations. In conjunction with our knowledge of the pathogen populations and coconut varieties, we hope this will lead to a better understanding of the disease ecology, and thus, the basis for periodic outbreaks of coconut lethal yellowing, which are now occurring in epidemic proportions in the Caribbean and Mesoamerica. (Texte intégral)
| Main Authors: | , , , |
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| Format: | conference_item biblioteca |
| Language: | eng |
| Published: |
s.n.
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| Subjects: | H10 - Ravageurs des plantes, |
| Online Access: | http://agritrop.cirad.fr/517503/ |
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