Publications

3560

Zebra chip (ZC) is a disease of potato, putatively caused by the vectorborne bacterium ‘Candidatus Liberibacter solanacearum’. Although ZC has been a major concern due its significant negative impact on both potato yield and quality, its effect on seed potato sprouting has been the subject of recent evaluations. The present study was conducted to determine whether variation in emergence is affected by the infection duration of ‘Ca. L. solanacearum’-infected seed potato prior to harvest. Furthermore, changes in pathogen detectability and titer levels in late-season-infected plants also were evaluated during and after cold storage. The rate of ZC-affected seed potato emergence following cold storage was not affected by the time of infection in the field, and the majority of ZC-infected tubers failed to sprout. Time to “seedling” emergence also was significantly longer in seed potato from plants infected ≥2 weeks before harvest. The small percentage of plants that emerged from ZC-affected seed potato produced stunted, nonvigorous plants that often died after a few weeks. The rate of successful ‘Ca. L. solanacearum’ detection increased during cold storage, suggesting a continued ‘Ca. L. solanacearum’–tuber interaction postharvest. After tubers were removed from cold storage and held at room temperature, ‘Ca. L. solanacearum’ titer started to increase. Although none of the tubers from plants infected 1 week before harvest exhibited any disease symptoms or tested positive for ‘Ca. L. solanacearum’ at harvest, up to 38% of these tubers tested positive following placement at room temperature after cold storage. Results of this study suggest that the role of seedborne ZC in disease epidemiology is likely to be insignificant. Furthermore, the findings of this study emphasized the importance of continued control measures until at least a week before harvest, and highlighted the need for improved methods of ‘Ca. L. solanacearum’ detection at harvest, especially in tubers infected late in the season.

Dichloromethane (DCM; CH2Cl2) is a widespread pollutant with anthropogenic and natural sources. Anaerobic DCM-dechlorinating bacteria use the Wood–Ljungdahl pathway, yet dechlorination reaction mechanisms remain unclear and the enzyme(s) responsible for carbon-chlorine bond cleavage have not been definitively identified. Of the three bacterial taxa known to carry out anaerobic dechlorination of DCM, ‘Candidatus Formimonas warabiya’ strain DCMF is the only organism that can also ferment non-chlorinated substrates, including quaternary amines (i.e., choline and glycine betaine) and methanol. Strain DCMF is present within enrichment culture DFE, which was derived from an organochlorine-contaminated aquifer. We utilized the metabolic versatility of strain DCMF to carry out comparative metaproteomics of cultures grown with DCM or glycine betaine. This revealed differential abundance of numerous proteins, including a methyltransferase gene cluster (the mec cassette) that was significantly more abundant during DCM degradation, as well as highly conserved amongst anaerobic DCM-degrading bacteria. This lends strong support to its involvement in DCM dechlorination. A putative glycine betaine methyltransferase was also discovered, adding to the limited knowledge about the fate of this widespread osmolyte in anoxic subsurface environments. Furthermore, the metagenome of enrichment culture DFE was assembled, resulting in five high quality and two low quality draft metagenome-assembled genomes. Metaproteogenomic analysis did not reveal any genes or proteins for utilization of DCM or glycine betaine in the cohabiting bacteria, supporting the previously held idea that they persist via necromass utilization.

This study presents the molecular detection of Candidatus Rickettsia andeanae and Ehrlichia sp. in Amblyomma pseudoconcolor Aragão, 1908 (Acari: Ixodidae) collected on a large hairy armadillo (Chaetophractus villosus (Desmarest, 1804)). On 12 October 2020, a specimen of C. villosus was found dead on the road in Río Negro province, Argentina. Molecular detection of Rickettsia and Ehrlichia agents was performed amplifying the gltA and 16S rRNA gene, respectively. One tick, determined morphologically and genetically as A. pseudoconcolor, was collected on C. villosus. The rickettsial agent detected in A. pseudoconcolor was identified as Candidatus Rickettsia andeanae. The Ehrlichia sp. strain showed high sequence similarity to different uncultured Ehrlichia sp. detected in horses, capybaras and Ixodes ornithorhynchi from Nicaragua, Brazil and Australia, respectively. The results of this study and previous findings suggest that A. pseudoconcolor may be a potential vector of some Rickettsia and Ehrlichia bacteria of unknown pathogenicity.

AbstractMolecular computing was used to investigate the possible causal agents of chilli crop samples showing mixed symptoms of yellow leaf curl and little leaf type diseases in the Uttar Pradesh province, India. Total genomic DNA was extracted from twenty-five samples and amplified by PCR using a universal primer pair for begomovirus and phytoplasma. Mixed infection samples show positive amplified products for begomovirus (DNA-A and betasatellite) and phytoplasma (16S rRNA and Sec A). The identified begomovirus from chilli samples was identified as a strain isolate of the previously described Chilli Leaf Curl Virus (94.2% nucleotide sequence identity), which is known to infectSolanum lycopersicon, in Oman, whereas the 16S rRNA was identified from the sourceCandidatus Phytoplasma trifolii(99.04% nucleotide sequence identity), which is known to infect Helichrysum flowering plants in India. Subsequently, molecular computing research based on phylogenetic interweaves, putative recombination, amino acid selection, and genetic diversity were investigated, revealing divergent evolutionary patterns with significant variation and recombination events. The majority of the sequence variations observed in begomovirus and phytoplasma were caused via inter- and intra-specific recombination. These findings could be the firstin silicocombined infection analysis of ChiLCV andCa.P.trifoliiin a chilli crop in India, revealing the potential adaption and evolution of begomovirus and phytoplasma to a new geographic range and crop.

‘ Candidatus Liberibacter asiaticus’ (CLas) is associated with the devastating citrus disease Huanglongbing (HLB). Young flushes are the center of the HLB pathosystem due to their roles in the psyllid life cycle and in the acquisition and transmission of CLas. However, the early events of CLas infection and how CLas modulates young flush physiology remain poorly understood. Here, transmission electron microscopy analysis showed that the mean diameter of the sieve pores decreased in young leaves of HLB-positive trees after CLas infection, consistent with CLas-triggered callose deposition. RNA-seq-based global expression analysis of young leaves of HLB-positive sweet orange with (CLas-Pos) and without (CLas-Neg) detectable CLas demonstrated a significant impact on gene expression in young leaves, including on the expression of genes involved in host immunity, stress response, and plant hormone biosynthesis and signaling. CLas-Pos and CLas-Neg expression data displayed distinct patterns. The number of upregulated genes was higher than that of the downregulated genes in CLas-Pos for plant−pathogen interactions, glutathione metabolism, peroxisome, and calcium signaling, which are commonly associated with pathogen infections, compared with the healthy control. On the contrary, the number of upregulated genes was lower than that of the downregulated genes in CLas-Neg for genes involved in plant−pathogen interactions and peroxisome biogenesis/metabolism. Additionally, a time-course quantitative reverse transcription-PCR-based expression analysis visualized the induced expression of companion cell-specific genes, phloem protein 2 genes, and sucrose transport genes in young flushes triggered by CLas. This study advances our understanding of early events during CLas infection of citrus young flushes.

A protocol to successfully transmit the huanglongbing (HLB) pathogen, ‘Candidatus Liberibacter asiaticus’, between citrus plants by using the Asian citrus psyllid (ACP) and an alternative way to help growers control ACP are proposed. Best results were obtained when pathogen acquisition by adults reared on fully symptomatic ‘Ca. Liberibacter asiaticus’-positive plants, latency, and inoculation occurred at ambient air temperatures ranging from 24 to 28°C and when a single infective adult ACP was confined for 7 days on soft, newly developing vegetative shoots (stages v2 to v4). No infection resulted from confinement of infective ACP adults on mature leaves (stage v6). Under the described conditions, single ACP adults could successfully transmit ‘Ca. Liberibacter asiaticus’ to an average of 56.5% (35 to 83%) of plantlets with v2 to v4 shoots growing in 0.3-liter tubes and to 80.5% (76 to 86%) of plants with v2 to v4 shoots growing in 4.7-liter pots. The use of single insects and plantlets reduces labor, space, and other resources necessary to undertake transmission tests. It also reduces time needed for transmission studies and should help accelerate research on HLB. The results were used to develop an index for favorability to infection (IFI) to determine orchard vulnerabilities to ‘Ca. Liberibacter asiaticus’. The IFI is based on the heterogeneous population of new shoots that occurs on tree canopies and may offer alternative or complementary alternatives to the laborious and costly insect surveys currently used in most instances to determine threshold levels for insecticide applications.