Publications

4364

Abstract Background Huanglongbing (HLB) is a major botanical pandemic of citrus crops caused by Candidatus Liberibacter asiaticus (Clas). It is important to understand the different mechanisms involved in interaction of pathogen with plants to develop novel management strategy against HLB. However, until now there has been no control strategy to manage this disease in vitro and on large scale in citrus grove. We found that, indigenous endophyte Bacillus subtilis L1-21, a patented strain isolated from healthy citrus tree, may have the potential to reduce the impact of pathogen through restructuring of core endophytes. Results A novel half-leaf method was developed to test the efficacy of B. subtilis L1-21 against Clas. Concentration of B. subtilis L1-21 at 104 cfu ml− 1 resulted in a 1000-fold reduction in Clas copy densities per gram of leaf midrib (107 to 104) by 4 d after treatment. With endophytes, where HLB incidence was reduced to < 3% and Clas copy density was reduced from 109 to 104 pathogen g− 1 of diseased leaf midrib. We found that 16 of 93 tree samples became Clas-free and functional pathways and pathogen resistance genes were regulated in diseased citrus trees after treatment. Conclusions This is the first large-scale study using an indigenous endophyte and shows its potential utility in sustainable disease management through strengthening the citrus microbiome.

Abstract Me.tha'no.thrix. N.L. neut. n. methanum methane; Gr. fem. n. thrix , hair; N.L. fem. n. Methanothrix , methane (‐producing) hair. Straight, rod‐shaped cells with flat ends, usually 0.8–1.3 μm wide by 2.0–6.0 μm long enclosed in a tubular sheath. Forms short (∼5–25 μm) to long (>150 μm) flexible chains of cells within the sheath. Nonmotile. Gram‐stain‐negative. Lipids contain myo ‐inositol, ethanolamine, and galactose as the polar head groups. Oxygen‐tolerant anaerobe. Organotrophic, splitting acetate into methane and CO 2 for energy generation. Some strains split formate into H 2 and CO 2 without producing methane. CO 2 can be reduced to methane in coculture with Geobacter spp. via direct interspecies electron transfer (DIET). Growth factors such as vitamins are stimulatory. Yeast extract is required, stimulatory or inhibitory, depending on the strain. NaCl is not required for growth. Optimal temperatures range from 34 to 37°C for mesophilic strains and 55 to 60°C for thermophilic strains; optimal pH range is 7.0–7.8. Gas vacuoles are generally found in thermophilic strains. Occur in both mesophilic and thermophilic anaerobic sludge digesters as well as anaerobic sediments. Synonymous with the genus Methanosaeta . DNA G + C content (mol%) : 51–61 (genome). Type species : Methanothrix soehngenii Huser et al. 1982, VL10. Taxonomic and Nomenclature Notes According to the List of Prokaryotic names with Standing in Nomenclature (LPSN), the taxonomic status of the genus Methanothrix is: correct name (last update, February 2025) * . LPSN classification: Archaea / Methanobacteriati / Methanobacteriota / Methanosarcinia / Methanosarcinales / Methanotrichaceae / Methanothrix The genus Methanothrix can also be recovered in the Genome Taxonomy Database (GTDB) as g__Methanothrix (version v220) ** . GTDB classification: d__Archaea / p__Halobacteriota / c__Methanosarcinia / o__Methanotrichales / f__Methanotrichaceae / g__Methanothrix * Meier‐Kolthoff et al. ( 2022 ). Nucleic Acids Res , 50 , D801 – D807 ; DOI: 10.1093/nar/gkab902 ** Parks et al. ( 2022 ). Nucleic Acids Res , 50 , D785 – D794 ; DOI: 10.1093/nar/gkab776

Abstract Me.tha.no.tri.cha.ce'ae. N.L. fem. n. Methanothrix type genus of the family; suff. – aceae ending to denote a family; N.L. fem. pl. n. Methanotrichaceae the Methanothrix family. Sheathed, rod‐shaped cells with flat ends, usually 0.8–1.3 μm wide by 2.0–6.0 μm long. Nonmotile. Gram‐stain‐negative. Oxygen‐tolerant anaerobe. Slow‐growing organotrophic, splitting acetate into methane and CO 2 for energy generation. Some strains split formate into hydrogen and CO 2 without generating methane. CO 2 can be reduced into methane when cocultured with electrogenic Geobacter spp. via direct interspecies electron transfer (DIET). Lipids contain myo ‐inositol, ethanolamine, and galactose as the polar head groups. Genome sequences have been determined for all described species. Habitats : Widely distributed in anaerobic river mud, paddy field soil, hot springs, thermal lakes, thermophilic and mesophilic anaerobic wastewater digestors treating domestic wastes, granular sludge, anaerobic fixed‐bed reactors, and other types of anaerobic systems. DNA G + C content (mol%) : 51–61 (Genome). Type genus : Methanothrix Huser et al. 1982, VL10. Taxonomic and Nomenclature Notes According to the List of Prokaryotic names with Standing in Nomenclature (LPSN), the taxonomic status of the family Methanotrichaceae is: correct name (last update, February 2025) * . LPSN classification: Archaea / Methanobacteriati / Methanobacteriota / Methanosarcinia / Methanosarcinales / Methanotrichaceae The family Methanotrichaceae can also be recovered in the Genome Taxonomy Database (GTDB) as f__Methanotrichaceae (version v220) ** . GTDB classification: d__Archaea / p__Halobacteriota / c__Methanosarcinia / o__Methanotrichales / f__Methanotrichaceae * Meier‐Kolthoff et al. ( 2022 ). Nucleic Acids Res , 50 , D801 – D807 ; DOI: 10.1093/nar/gkab902 ** Parks et al. ( 2022 ). Nucleic Acids Res , 50 , D785 – D794 ; DOI: 10.1093/nar/gkab776

Liberibacter is a bacterial group causing different diseases and disorders in plants. Among liberibacters, Candidatus Liberibacter solanaceraum (CLso) produces disorders in several species mainly within Apiaceae and Solanaceae families. CLso isolates are usually grouped in defined haplotypes according to single nucleotide polymorphisms in genes associated with ribosomal elements. In order to characterize more precisely isolates of CLso identified in potato in Spain, a Multilocus Sequence Analysis (MLSA) was applied. This methodology was validated by a complete analysis of ten housekeeping genes that showed an absence of positive selection and a nearly neutral mechanism for their evolution. Most of the analysis performed with single housekeeping genes, as well as MLSA, grouped together isolates of CLso detected in potato crops in Spain within the haplotype E, undistinguishable from those infecting carrots, parsnips or celery. Moreover, the information from these housekeeping genes was used to estimate the evolutionary divergence among the different CLso by using the concatenated sequences of the genes assayed. Data obtained on the divergence among CLso haplotypes support the hypothesis of evolutionary events connected with different hosts, in different geographic areas, and possibly associated with different vectors. Our results demonstrate the absence in Spain of CLso isolates molecularly classified as haplotypes A and B, traditionally considered causal agents of zebra chip in potato, as well as the uncertain possibility of the present haplotype to produce major disease outbreaks in potato that may depend on many factors that should be further evaluated in future works.

AbstractCulicoidesbiting midges (Diptera: Ceratopogonidae) are disease vectors responsible for the transmission of several viruses of economic and animal health importance. The recent deployment ofWolbachiawith pathogen-blocking capacity to control viral disease transmission by mosquitoes has led to a focus on the potential use of endosymbionts to control arboviruses transmitted by other vector species. Previous screens ofCulicoideshave described the presence ofCandidatusCardinium hertigii (Bacteroidetes). However, the biological impact of this symbiont is yet to be uncovered and awaits a suitable system to studyCardinium-midge interactions. To identify candidate species to investigate these interactions, accurate knowledge of the distribution of the symbiont withinCulicoidespopulations is needed. We used a sensitive nested PCR assay to screenCardiniuminfection in 337 individuals of 25Culicoidesspecies from both Palearctic and Afrotropical regions. Infections were observed in several vector species includingC. imicolaand the pulicaris complex (C. pulicaris, C. bysta, C. newsteadiandC. punctatus) with prevalence ranging from low and intermediate, to fixation. Infection inC. pulicariswas very rare in comparison to a previous study, and there is evidence the prior record of high prevalence represents a laboratory contamination error. Phylogenetic analysis based on the Gyrase B gene sequence grouped all new isolates within “group C” of the genus, a clade which has to date been exclusively described inCulicoides. Through a comparison of our results with previous screens, we evaluate the suitability ofCardinium-infected species for future work pertaining to the symbiont.

AbstractAster Yellows phytoplasma (AYp;Candidatus (Ca.)Phytoplasma asteris) is an obligate bacterial pathogen that is the causative agent of multiple diseases in herbaceous plants. While this phytoplasma has been examined in depth for its disease characteristics, knowledge about the spatial and temporal dynamics of pathogen spread is lacking. The phytoplasma is found in plant’s phloem and is vectored by leafhoppers (Cicadellidae: Hemiptera), including the aster leafhopper,Macrosteles quadrilineatusForbes. The aster leafhopper is a migratory insect pest that overwinters in the southern United States, and historical data suggest these insects migrate from southern overwintering locations to northern latitudes annually, transmitting and driving phytoplasma infection rates as they migrate. A more in-depth understanding of the spatial, temporal and genetic determinants of Aster Yellows disease progress will lead to better integrated pest management strategies for Aster Yellows disease control. Carrot,Daucus carotaL., plots were established at two planting densities in central Wisconsin and monitored during the 2018 growing season for Aster Yellows disease progression. Symptomatic carrots were sampled and assayed for the presence of the Aster Yellows phytoplasma. Aster Yellows disease progression was determined to be significantly associated with calendar date, crop density, location within the field, and phytoplasma subgroup.

The psyllids Cacopsylla melanoneura and Cacopsylla picta reproduce on apple (Malus × domestica) and transmit the bacterium ‘Candidatus Phytoplasma mali’, the causative agent of apple proliferation. Adult psyllids were collected by the beating-tray method from lower and upper parts of the apple tree canopy in the morning and in the afternoon. There was a trend of catching more emigrant adults of C.melanoneura in the morning and in the lower part of the canopy. For C.melanoneura remigrants, no differences were observed. The findings regarding the distribution of adults were reflected by the number of nymphs collected by wash-down sampling. The density of C.picta was too low for a statistical analysis. The vector monitoring and how it is commonly performed, is suitable for estimating densities of C.melanoneura. Nevertheless, above a certain temperature threshold, prediction of C.melanoneura density might be skewed. No evidence was found that other relatively abundant psyllid species in the orchard, viz. Baeopelma colorata, Cacopsylla breviantennata, Cacopsylla brunneipennis, Cacopsylla pruni and Trioza urticae, were involved in ‘Candidatus Phytoplasma mali’ transmission. The results of our study contribute to an advanced understanding of insect vector behavior and thus have a practical impact for an improved field monitoring.