ABSTRACT
Despite the importance of viral strains/variants as agents of emerging diseases, genetic and evolutionary processes affecting their ecology are not fully understood. To get insight into this topic, we assessed the population and spatial dynamic parameters of citrus leprosis virus C (CiLV-C, genus Cilevirus, family Kitaviridae). CiLV-C is the etiological agent of citrus leprosis disease, a non-systemic infection considered the main viral disorder affecting citrus orchards in Brazil. Overall, we obtained 18 complete or near-complete viral genomes, 123 complete nucleotide sequences of the open reading frame (ORF) encoding the putative coat protein, and 204 partial nucleotide sequences of the ORF encoding the movement protein, from 430 infected Citrus spp. samples collected between 1932 and 2020. A thorough examination of the collected dataset suggested that the CiLV-C population consists of the major lineages CRD and SJP, unevenly distributed, plus a third one called ASU identified in this work, which is represented by a single isolate found in an herbarium sample collected in Asuncion, Paraguay, in 1937. Viruses from the three lineages share about 85% nucleotide sequence identity and show signs of inter-clade recombination events. Members of the lineage CRD were identified both in commercial and non-commercial citrus orchards. However, those of the lineages SJP were exclusively detected in samples collected in the citrus belt of São Paulo and Minas Gerais, the leading Brazilian citrus production region, after 2015. The most recent common ancestor of viruses of the three lineages dates back to, at least, â¼1500 years ago. Since citrus plants were introduced in the Americas by the Portuguese around the 1520s, the Bayesian phylodynamic analysis suggested that the ancestors of the main CiLV-C lineages likely originated in contact with native vegetation of South America. The intensive expansion of CRD and SJP lineages in Brazil started probably linked to the beginning of the local citrus industry. The high prevalence of CiLV-C in the citrus belt of Brazil likely ensues from the intensive connectivity between orchards, which represents a potential risk toward pathogen saturation across the region.
ABSTRACT
BACKGROUND: Citrus variegated chlorosis (CVC) is an important citrus disease caused by the sharpshooter-transmitted bacterium Xylella fastidiosa subsp. pauca. Information about the efficacy of its disease management is bounded to either inoculum reduction or vector control. This study aimed to assess the role of different frequencies of roguing of symptomatic trees combined with different chemical control programs for the sharpshooters on CVC temporal progress. The experimental area was set up in October 2005 and had a 3 × 3 factorial design. Symptomatic tree removal intervals were every 28, 56, and 112 days to May 2012. Vector control treatments were no control, program A (PA), and program B (PB). Contact insecticides were sprayed every 28 (PA) or 14 (PB) days. Trees within both programs were treated with systemic and foliar insecticides to October 2008. After this, systemic insecticides were discontinued and only foliar treatments were applied. The number of diseased trees and the sharpshooter population were assessed to April 2015. RESULTS: Detection of the first symptomatic trees was similar for all treatments and occurred, on average, in month 50 after planting. Sharpshooter population and cumulative disease incidence were similar for all roguing intervals and between vector control programs, differing in plots with no control. We observed a reduction over 85% in disease incidence for both PA and PB compared with no control. CONCLUSION: These results support systematic control of sharpshooters as an efficient strategy for reducing CVC progress. © 2021 Society of Chemical Industry.
Subject(s)
Anemia, Hypochromic , Citrus , Incidence , Plant Diseases/prevention & control , XylellaABSTRACT
Huanglongbing (HLB) is a citrus disease of worldwide importance, associated with the presence of Candidatus Liberibacter asiaticus (Las) and vectored by the psyllid Diaphorina citri in Asia and the Americas. To properly manage HLB, removal of inoculum sources and control of the psyllid are undertaken. We evaluated the percentage of the psyllid population with Las, sampled from yellow sticky traps over a three-year period and its relationship with insect population, regions, season of the year, and HLB management in citrus areas in the southwestern, central, and northern regions of São Paulo (SP) and southwestern region of Minas Gerais states, Brazil. In each reading, up to 50 psyllids per region were collected and detection of Las in individual psyllids were made by quantitative polymerase chain reaction. The percentage of psyllids with Las-an average of 65.3%-was constant throughout the year in the southwestern region of SP state, while showing an increase from spring to autumn when sampled from central to northern regions. The proportion of psyllids carrying Las from each region and year period were compared by a proportion test and spectral density analysis. The proportion of psyllids carrying Las evaluated in the same region in different seasons presented statistical differences in central (Araraquara) and southwestern (Santa Cruz do Rio Pardo) regions in 2015, with higher values in the first semester (summer and autumn) than in the second semester (winter and spring). Orchards with poor HLB management had higher incidence of psyllids with Las. Spectral density analysis indicated that good management areas had 50% less relevant peaks of psyllids with Las than in areas with poor HLB management practices. The relationship between the percentage of psyllids carrying Las and the number of captured psyllids in the region in a given time denotes the most critical intake time for HLB spread in citrus orchards. The reduction in the population of psyllids carrying Las is a direct benefit from the use of good management practices.
