First Report of an Aster Yellows Subgroup 16SrI-B Phytoplasma Infecting Chayote in Costa Rica

An outbreak of a witches' broom disease affected approximately 20% of plants in several chayote (Sechium edule (Jacq.) Schwartz) fields in the commercial production area of the Ujarrás Valley, Cartago Province, Costa Rica during 2000 and 2001. Affected chayote plants exhibited symptoms, including basal proliferation with severe foliage reduction, aborted flowers, and deformed fruits, suggestive of phytoplasmal infection. Two other symptomatic cucurbit species growing near the chayote fields were also identified. These species were tacaco plants (S. tacaco (Pitt.) C. Jeffrey), an edible cucurbit for domestic marketing in Costa Rica, showing severe size reduction of leaves and fruits, and Rytidostylis carthaginensis (Jacq.) Kuntze, a weed in chayote and tacaco fields, exhibiting abnormal tendril proliferation. Plants were analyzed for phytoplasma infection by a nested polymerase chain reaction (PCR) assay, using the universal rRNA primer pair P1/P7 followed by R16F2n/R16R2 (2). Phytoplasmas were detected in all symptomatic samples (18 chayote, 6 tacaco, and 3 weed) tested but were undetectable in all asymptomatic samples (10 chayote, 6 tacaco, and 2 weed). Restriction fragment length polymorphism (RFLP) analysis of PCR products (16S rDNA sequences) by separate digestion with eight restriction enzymes (RsaI, HhaI, KpnI, BfaI, HaeIII, HpaII, AluI, MseI) revealed that a phytoplasma belonging to subgroup 16SrI-B in the aster yellows phytoplasma group (16SrI) was associated with chayote witches' broom (CWB). The same or very similar phytoplasmas were found in both symptomatic tacaco and R. carthaginensis plants. Phylogenetic analysis of 16SrDNA sequences also confirmed the CWB phytoplasma to be most similar to members of subgroup 16SrI-B. Similar diseases in chayote and other cucurbits have been reported in Brazil (3), Taiwan (1), and Mexico (4). The CWB phytoplasma differs from the phytoplasma (16SrIII-J subgroup) associated with chayote in Brazil. The identities of phytoplasmas associated with cucurbits in Taiwan and Mexico are unknown. The occurrence of an aster yellows group phytoplasma in chayote may pose a potential threat to continued production and exportation of this cash crop. To our knowledge, this is the first report of 16SrI-B subgroup phytoplasmas in naturally infected cucurbits in Costa Rica.Universidad de Costa Rica/[801-A5-582]/UCR/Costa RicaInternational Atomic Energy Agency/[]/IAEA/AustriaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Biología Celular y Molecular (CIBCM

Differential Symptomology, Susceptibility, and Titer Dynamics Manifested by Phytoplasma-Infected Periwinkle and Tomato Plants

Phytoplasmas are intracellular pathogenic bacteria that infect a wide range of plant species, including agriculturally important crops and ornamental trees. However, our understanding of the relationship between symptom severity, disease progression, and phytoplasma concentration remains limited due to the inability to inoculate phytoplasmas mechanically into new plant hosts. The present study investigated phytoplasma titer dynamics and symptom development in periwinkle and tomato, both infected with the same potato purple top (PPT) phytoplasma strain using a small seedling grafting approach. Virescence, phyllody, and witches’-broom (WB) symptoms sequentially developed in periwinkle, while in tomato plants, big bud (BB, a form of phyllody), cauliflower-like inflorescence (CLI), and WB appeared in order. Results from quantitative polymerase chain reaction (qPCR) targeting the PPT phytoplasma’s 16S rRNA gene revealed that in both host species, phytoplasma titers differed significantly at different infection stages. Notably, the highest phytoplasma concentration in periwinkles was observed in samples displaying phyllody symptoms, whereas in tomatoes, the titer peaked at the BB stage. Western blot analysis, utilizing an antibody specific to PPT phytoplasma, confirmed substantial phytoplasma presence in samples displaying phyllody and BB symptoms, consistent with the qPCR results. These findings challenge the conventional understanding that phytoplasma infection dynamics result in a higher titer at later stages, such as WB (excessive vegetative growth), rather than in the early stage, such as phyllody (abnormal reproductive growth). Furthermore, the PPT phytoplasma titer was markedly higher in periwinkles than in tomato plants, indicating differing susceptibilities between the hosts. This study reveals distinct host responses to PPT phytoplasma infection, providing valuable insights into phytoplasma titer dynamics and symptom development, with implications for the future management of agricultural disease

On Combining Alignment Techniques

<p><b>A)</b> Neighbor-joining tree built using blast-based average nucleotide identity (ANIb) estimates calculated using JSpecies. Pairwise distances are provided in the inset table. As native ANIb values connote similarity measures; specifically, the proportion of identical residues among aligned segments expressed as a percentage; distance measures are obtained by taking complements with respect to 100%. ANIb considers similarity observed in all regions of the respective genomes where pairwise alignments using blastn are possible. <b>B)</b> Bayesian phylogeny produced using a codon-based model of DNA evolution applied to a concatemer of 29 reliably aligned, conserved protein-coding genes (6,618 codons in total). Branch lengths correspond to the number of nucleotide substitutions per codon. Posterior probabilities of the inferred branching patterns are indicated on the tree.</p

Candidate cell wall membrane-anchored, secreted proteins in NJAY.

<p>Candidate cell wall membrane-anchored, secreted proteins in NJAY.</p

Contigs from NJAY chromosomal assembly exhibiting hits to PMUs of the AY-WB chromosome.

<p>Contigs from NJAY chromosomal assembly exhibiting hits to PMUs of the AY-WB chromosome.</p

Homology-supported candidate NJAY secreted proteins to be released as soluble biomolecules.

<p>Homology-supported candidate NJAY secreted proteins to be released as soluble biomolecules.</p

Sub-assembled extrachromosomal NJAY sequences.

<p>Sub-assembled extrachromosomal NJAY sequences.</p

Non-membrane bound secreted protein candidates in NJAY lacking evident homology with such proteins in AY-WB.

<p>Non-membrane bound secreted protein candidates in NJAY lacking evident homology with such proteins in AY-WB.</p

Conserved genes present as single copies in AY-WB, CX, NJAY, OY-M, PAa and SLY.

<p>Conserved genes present as single copies in AY-WB, CX, NJAY, OY-M, PAa and SLY.</p