Publications

4696

‘ Candidatus Liberibacter solanacearum’ (Lso) is a phloem-limited pathogen associated with devastating diseases in members of the Solanaceae and Apiaceae and vectored by several psyllid species. Different Lso haplotypes have been identified, and LsoA and LsoB are responsible for diseases in Solanaceae crops. Our efforts are aimed at identifying pathogenicity factors used by this bacterium to thrive in different hosts. Bacterial secreted proteins can play a role in host colonization or the manipulation of the host immune responses; these proteins are called effectors. In this study, we identified six LsoB-specific proteins with a conserved secretion motif as well as a conserved N-terminal domain in the mature protein. These proteins had different expression and secretion patterns but a similar subcellular localization in Nicotiana benthamiana leaves, suggesting that they play different roles regardless of their conserved secretion motif. One of these proteins, CKC_04425, was expressed at high levels in the insect vector and the host plant, indicating that it could play a role in both the plant and insect hosts, whereas the others were mainly expressed in the plant. One protein, CKC_05701, was able to efficiently suppress programmed cell death and reactive oxygen species production, suggesting that it may have a virulence role in LsoB-specific pathogenesis.

Huanglongbing (HLB), caused by phloem-limited ‘ Candidatus Liberibacter asiaticus’ (CLas), is the primary limiting factor of production in most citrus regions of the world. After infection, CLas is transported systemically throughout the phloem tissues following the source-sink movement. Split-root rhizoboxes and one-sided graft inoculation above the split trunk was used to understand if the vertical distance of the inoculum source and different anatomical structures (grafted or seedling trees) can affect the speed of the CLas movement, as well as the effects of the seasonality on these movements. The time for CLas to reach the roots was not affected by either distance of the inoculum source or tree type. The seasonal infection period appears to have an important effect on CLas movement. Trees inoculated in the summer had fast and uniform movement (first detection at 4 weeks after inoculation). Plants inoculated in the winter had a slow and uneven movement (first CLas detection at 14 weeks after inoculation). Our results indicate that summer and spring are the seasons of CLas down and lateral movement, but this is independent of the vertical distance of the inoculum source or anatomical structures of the plants. The findings from this study aid in the management of HLB in the field, as well as improve the methods for CLas detection. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

El cultivo de chile en el norte centro de México es dañado por la infección causada por Candidatus Phytoplasma trifolii. Los síntomas de la enfermedad incluyen clorosis, deformación foliar, enanismo y sobredesarrollo floral (yema grande) con necrosis de pistilo y anteras. La distribución de yemas grandes en la planta es irregular. Ello sugiere que el patógeno o sus efectores se moverían irregularmente dentro de la planta. Por lo tanto, el objetivo de este trabajo fue determinar la presencia de Candidatus Phytoplasma trifolii en diferentes órganos de plantas de chile con síntomas de yema grande. Plantas enfermas de chile tipo Mirasol fueron recolectadas en una parcela comercial en Zacatecas, México, y sus raíces, tallos, hojas, frutos y yemas grandes fueron analizadas por PCR universal y anidada para detectar la presencia del fitoplasma. El patógeno fue detectado en cinco de ocho plantas analizadas, en por lo menos un órgano de cada planta; sin embargo, su distribución dentro de las plantas fue irregular. El porcentaje de detección fue 33.3, 62.5, 70, 80 y 100 % en raíces, hojas, tallos, frutos y yemas grandes, respectivamente. En frutos de plantas de chile sintomáticas a yema grande, el fitoplasma fue detectado en el pedúnculo, placenta y semillas.

Microorganisms called anammox bacteria are efficient in removing bioavailable nitrogen from many natural and human-made environments. They exist in almost every anoxic habitat where both ammonium and nitrate/nitrite are present.

The almond, a commercially important tree nut crop worldwide, is native to the Mediterranean region. Stone fruit trees are affected by at least 14 ‘Candidatus Phytoplasma’ species globally, among which ‘Candidatus Phytoplasma asteris’ is one of the most widespread phytoplasma infecting Prunus dulcis, causing aster yellows disease. Recently, almond plantations of Nauni region were consistently affected by phytoplasma, as evidenced by visible symptoms, fluorescent microscopic studies and molecular characterization. During several surveys from May to September 2020–2022, almond aster yellows phytoplasma disease showing symptoms such as chlorosis, inward rolling, reddening, scorching and decline with an incidence as high as 40%. Leaf samples were collected from symptomatic almond trees and the presence of phytoplasma was confirmed through fluorescent microscopic studies by employing DAPI (4, 6-diamino-2-phenylindole) that showed distinctive light blue flourescent phytoplasma bodies in phloem sieve tube elements. The presence of phytoplasma in symptomatic almond trees was further confirmed using nested PCR with specific primer pairs followed by amplification of 16S rDNA and 16S-23S rDNA intergenic spacer (IS) fragments. Sequencing and BLAST analysis of expected amplicon of the 16S rDNA gene confirmed that the almond phytoplasma in Himachal Pradesh was identical to the aster yellows group phytoplasma. Phylogenetic analysis of 16S rDNA almond phytoplasma also grouped ‘Prunus dulcis’ aster yellows phytoplasma within 16SrI-B subgroup showed 94% nucleotide identity with ‘Prunus dulcis’ phytoplasma PAEs3 and ‘Prunus dulcis’ phytoplasma PAE28 from Iran. This research presents the first host report of ‘Candidatus Phytoplasma asteris’ infecting almonds in India, expanding the knowledge of the diversity and distribution of phytoplasma strains affecting almond trees globally.