RESUMEN

Citrus greening (Huanglongbing, HLB) is one of the most destructive diseases of citrus worldwide. In South Asia HLB has been known for more than a century, while in Americas the disease was found relatively recently. HLB is associated with three species of 'Candidatus Liberibacter' among which 'Ca. Liberibacter asiaticus' (CLas) has most wide distribution. Recently, a number of studies identified different regions in the CLas genome with variable number of tandem repeats (VNTRs) that could be used for examination of CLas diversity. One of the objectives of the work presented here was to further validate the VNTR analysis-based approach by assessing the stability of these repeats upon multiplication of the pathogen in a host over an extended period of time and upon its passaging from a host to a host using CLas populations from Florida. Our results showed that the numbers of tandem repeats in the four loci tested display very distinguishable "signature profiles" for the two Florida-type CLas haplotype groups. Remarkably, the profiles do not change upon passage of the pathogen in citrus and psyllid hosts as well as after its presence within a host over a period of five years, suggesting that VNTR analysis-based approach represents a valid methodology for examination of the pathogen populations in various geographical regions. Interestingly, an extended analysis of CLas populations in different locations throughout Florida and in several countries in the Caribbean and Central America regions and in Mexico where the pathogen has been introduced recently demonstrated the dispersion of the same haplotypes of CLas. On the other hand, these CLas populations appeared to differ significantly from those obtained from locations where the disease has been present for a much longer time.

Asunto(s)

Citrus/microbiología , Repeticiones de Minisatélite/genética , Enfermedades de las Plantas/microbiología , Rhizobiaceae/genética , Rhizobiaceae/fisiología , Animales , Región del Caribe , América Central , ADN Bacteriano/genética , Florida , Variación Genética , Geografía , Haplotipos , Hemípteros/microbiología , Interacciones Huésped-Patógeno , México , Reacción en Cadena de la Polimerasa , Polimorfismo Genético , Dinámica Poblacional

RESUMEN

Citrus tristeza virus (CTV) is the most destructive viral pathogen of citrus and has been an important concern for the citrus industry in the Dominican Republic. Earlier studies documented widespread distribution of mild isolates of the T30 genotype, which caused no disease in the infected trees, and a low incidence of isolates of the VT and T3 genotypes, which were associated with economically damaging decline and stem-pitting symptoms in sweet orange and Persian lime, the two major citrus varieties grown in the Dominican Republic. In light of the dramatic increase in the number of severely diseased citrus trees throughout the country over the last decade, suggesting that field populations of CTV have changed, we examined the CTV pathosystem in the Dominican Republic to assess the dynamics of virus populations. In this work, we characterized the molecular composition of 163 CTV isolates from different citrus-growing regions. Our data demonstrate a dramatic change in CTV populations, with the VT genotype now widely disseminated throughout the different regions and with the presence of two new virus genotypes, T36 and RB. Multiple infections of trees resulted in development of complex virus populations composed of different genotypes.