Publications

4369

The devastating citrus disease huanglongbing (HLB) associated with the phloem-limited bacteria Candidatus Liberibacter asiaticus (CLas) has caused a more than 70% reduction in citrus production since its discovery in Florida in 2005. Most citrus scion cultivars are sensitive to HLB, whereas some cultivars used as rootstocks are tolerant. Using such tolerant rootstocks can help trees to cope better with the disease’s impact. Evaluating rootstock effects on a grafted scion in the field takes many years, but shorter-term evaluation is imperative to aid in rootstock selection for an HLB-endemic production environment. In this study, we investigated grafted healthy and CLas-infected citrus trees under controlled greenhouse conditions. The objectives were to identify traits suitable for assessing grafted tree tolerance in advance of longer-term field studies and aiding in the selection of superior rootstock cultivars. We assessed 10 commercially important rootstocks grafted with ‘Valencia’ sweet orange scion and with known field performance. At 6, 9, 15, and 21 months after graft inoculation (mai), leaf CLas titers were determined and canopy health was evaluated. Plants were destructively sampled at 21 mai to assess plant biomasses and other physiological and horticultural variables. There was little influence of the rootstock cultivar on CLas titers. Surprisingly, few HLB foliar disease symptoms and no differences in soluble and nonsoluble carbohydrate concentrations were measured in infected compared with healthy plants, despite high CLas titers and significant reductions in plant biomasses. Most trees on rootstocks with trifoliate orange parentage were less damaged by HLB than other rootstocks, although results did not always agree with reported field performance. Among the different variables measured, leaf size appeared to be most predictive for grafted tree assessment of HLB sensitivity. The results of this study provide a better understanding of the strengths and weaknesses of assessing rootstock influence on grafted tree performance in a controlled greenhouse environment. Although such studies provide valuable information for cultivar tolerance to HLB, other rootstock traits will ultimately contribute to field survival and productivity in an HLB endemic production environment.

Huanglongbing (HLB) is currently the most devastating disease of citrus worldwide. Both bacteria ‘Candidatus Liberibacter asiaticus’ (CLas) and ‘Candidatus Liberibacter americanus’ (CLam) are associated with HLB in Brazil but with a strong prevalence of CLas over CLam. Conventionally, HLB management focuses on controlling the insect vector population (Diaphorina citri; also known as Asian citrus psyllid [ACP]) by spraying insecticides, an approach demonstrated to be mostly ineffective. Thus, development of novel, more efficient HLB control strategies is required. The multifunctional bacterial outer membrane protein OmpA is involved in several molecular processes between bacteria and their hosts and has been suggested as a target for bacterial control. Curiously, OmpA is absent in CLam in comparison with CLas, suggesting a possible role in host interaction. Therefore, in the current study, we have treated ACPs with different OmpA-derived peptides, aiming to evaluate acquisition of CLas by the insect vector. Treatment of psyllids with 5 µM of Pep1, Pep3, Pep5, and Pep6 in artificial diet significantly reduced the acquisition of CLas, whereas increasing the concentration of Pep5 and Pep6 to 50 µM abolished this process. In addition, in planta treatment with 50 µM of Pep6 also significantly decreased the acquisition of CLas, and sweet orange plants stably absorbed and maintained this peptide for as long as 3 months post the final application. Together, our results demonstrate the promising use of OmpA-derived peptides as a novel biotechnological tool to control CLas.

The considerable economic losses in citrus associated with ‘Candidatus Liberibacter’ and ‘Candidatus Phytoplasma’ presence have alerted all producing regions of the world. In Chile, none of these bacteria have been reported in citrus species. During the years 2017 and 2019, 258 samples presenting symptoms similar to those associated with the presence of these bacteria were examined. No detection of ‘Ca. Liberibacter’ associated with “huanglongbing” disease was obtained in the tested samples; therefore, this quarantine pest is maintained as absent in Chile. However, 14 plants resulted positive for phytoplasmas enclosed in subgroups 16SrV-A (12 plants) and 16SrXIII-F (2 plants). Although they have been found in other plant species, this is the first report of these phytoplasmas in citrus worldwide.

Tomato (Solanum lycopersicum) is one of the most financially important vegetable crops. It is a species belonging to the Solanaceae family and is cultivated in many countries, including Turkey. The natural presence of ‘Candidatus Phytoplasma solani’ (‘Ca. P. solani’) from the Stolbur group (16SrXII) in tomato plants is extensively characterized based on the 16S rRNA gene worldwide. Tomato plants displaying abnormality and sterility of flower, purpling, and bushy appearance were observed in the Van province, Turkey. DNA extraction from tomato leaves was performed, and the extracted DNA was used to amplify 16S rRNA sequences using universal primer pairs by double PCR assays. After confirming the presence of the probable agent (‘Ca. P. solani’), nested PCR testing was performed using an appropriate primer set amplifying the SecY and Vmp1 genes of the same DNAs. Amplified PCR yields were then cloned into a pGEM T-Easy vector and sequenced by New Generation System (NGS). Sequenced 1438 bp nucleotides for Vmp1 gene (MN104838) and 905 bp nucleotides for SecY gene (MN125054) revealed 97.38% and 100% maximum nucleotide similarity with formerly published Vmp1 and SecY gene sequences of ‘Ca. P. solani’ species belonged to the Stolbur group (16Sr-XII), respectively. According to the phylogenetic tree created using our gene sequences from ‘Ca. P. solani’, Vmp1, and SecY gene sequences showed a highly phylogenetic affinity with the same sequences of the same agent from Serbia and France, respectively. To the best of our knowledge, this study is the first report to reveal the phylogenetic relationships of ‘Ca. P. solani’ in stolbur group (16Sr XII-A) using SecY and Vmp1 genes in the tomato plant in Turkey based on the non-ribosomal genes.

AbstractThe human gut microbiome plays an important role in health, but its archaeal diversity remains largely unexplored. In the present study, we report the analysis of 1,167 nonredundant archaeal genomes (608 high-quality genomes) recovered from human gastrointestinal tract, sampled across 24 countries and rural and urban populations. We identified previously undescribed taxa including 3 genera, 15 species and 52 strains. Based on distinct genomic features, we justify the split of theMethanobrevibacter smithiiclade into two separate species, with one represented by the previously undescribed ‘CandidatusMethanobrevibacter intestini’. Patterns derived from 28,581 protein clusters showed significant associations with sociodemographic characteristics such as age groups and lifestyle. We additionally show that archaea are characterized by specific genomic and functional adaptations to the host and carry a complex virome. Our work expands our current understanding of the human archaeome and provides a large genome catalogue for future analyses to decipher its impact on human physiology.