Characterization of Pterotylenchus cecidogenus in Desmodium ovalifolium cover crop from oil palm plantations in central Colombia.

Until recently, the stem gall nematode Pterotylenchus cecidogenus was only registered in eastern Colombia. However, the disease has recently been observed in central Colombian oil palm plantations that use Desmodium ovalifolium as a cover crop. Soil, root, stem, and leaf samples were collected from D. ovalifolium. Plants showed foliar yellowing, leaf drying, and galls within stem nodes. Nematodes were identified, and the distribution, population density, and relative importance of different genera were determined. We performed morphometric and molecular identification of nematodes associated with gall symptoms. The D2-D3 segment of the large subunit-28S of ribosomal ribonucleic acid (RNA) and internal transcribed spacer (ITS) was sequenced, and phylogenetic analysis was performed. P. cecidogenus mainly occurred in the galls and to a lesser extent in the roots and soil. Nematodes were not found in leaf or inflorescence tissue. Morphological and morphometric data confirm the presence of P. cecidogenus in the stems of D. ovalifolium with gall symptoms. This study is the first to report deoxyribonucleic acid (DNA) sequences of P. cecidogenus. Based on D2-D3 and ITS partial sequences, P. cecidogenus is a sister species of the leaf-galling nematode Ditylenchus phyllobius (Sinm. Orrina phyllobia).

Genomic Variability of Phytophthora palmivora Isolates from Different Oil Palm Cultivation Regions in Colombia.

Palm oil is the most consumed vegetable oil globally, and Colombia is the largest palm oil producer in South America and fourth worldwide. However, oil palm plantations in Colombia are affected by bud rot disease caused by the oomycete Phytophthora palmivora, leading to significant economic losses. Infection processes by plant pathogens involve the secretion of effector molecules, which alter the functioning or structure of host cells. Current long-read sequencing technologies provide the information needed to produce high-quality genome assemblies, enabling a comprehensive annotation of effectors. Here, we describe the development of genomic resources for P. palmivora, including a high-quality genome assembly based on long and short-read sequencing data, intraspecies variability for 12 isolates from different oil palm cultivation regions in Colombia, and a catalog of over 1,000 candidate effector proteins. A total of 45,416 genes were annotated from the new genome assembled in 2,322 contigs adding to 165.5 Mbp, which represents an improvement of two times more gene models, 33 times better contiguity, and 11 times less fragmentation compared with currently available genomic resources for the species. Analysis of nucleotide evolution in paralogs suggests a recent whole-genome duplication event. Genetic differences were identified among isolates showing variable virulence levels. We expect that these novel genomic resources contribute to the characterization of the species and the understanding of the interaction of P. palmivora with oil palm and could be further exploited as tools for the development of effective strategies for disease control.

Molecular identification of Bursaphelenchus cocophilus associated to oil palm (Elaeis guineensis) crops in Tibu (North Santander, Colombia).

The red ring nematode (Bursaphelenchus cocophilus (Cobb) Baujard 1989) has been registered in oil palm crops in the North, Central and Eastern zones of Colombia. In Tibu (North Santander), there are doubts regarding the diagnostic and identity of the disease. Oil palm crops in Tibu with the external and internal symptoms were inspected, and tissue samples were taken from different parts of the palm. The refrigerated samples were carried to the laboratory of Oleoflores in Tibu for processing. The light microscopy was used for the quantification and morphometric identification of the nematodes. Specimens of the nematode were used for DNA extraction, to amplify the segment D2-D3 of the large subunit of ribosomal RNA (28S) and perform BLAST and a phylogeny study. The most frequently symptoms were chlorosis of the young leaves, thin leaflets, collapsed, and dry lower leaves, beginning of roughening, accumulation of arrows and short leaves. Bursaphelenchus, was recovered in most of the tissues from the samples analyzed: stem, petiole bases, inflorescences, peduncle of bunches, and base of arrows in variable populations. The morphometric data and sequences obtained for the segment D2-D3 confirms to B. cocophilus as the causal agent of red ring disease on oil palms in the study area. For our knowledge, this study reports the first partial sequences of segment D2-D3 of B. cocophilus in oil palm in Colombia.

Ganoderma zonatum Is the Causal Agent of Basal Stem Rot in Oil Palm in Colombia.

Basal stem rot (BSR), caused by Ganoderma spp., is one of the most important emerging oil palm diseases in Colombia, and is restricted to two oil palm production areas in the country. To identify the causal agent of the disease, basidiocarp of oil palms affected by BSR were used to prepare isolates, and their pathogenicity was then assessed in pre-nursery plants. Four-month-old oil palm seedlings were inoculated with rubber wood (Hevea brasiliensis) blocks colonized with dikaryotic mycelia of Ganoderma. The incidence, severity, and symptoms of the pathogen were assessed. A multiregional analysis (ITS, rpb2, and tef1-α) was carried out to identify the isolates; all isolates were determined to be Ganoderma zonatum. Phylogenetic analyses with the three regions yielded concordant phylogenetic information and supported the distinction of the isolates with high bootstrap support. Seven isolates (CPBsZN-01-29, CPBsZN-02-30, CPBsZN-03-31, CPBsZN-04-34, CPBsZN-05-35, CPBsZN-06-36, and CPBsZN-07-38) were pathogenic in oil palm, with incidences greater than 90% and a maximum severity of 34%, and the highest severity index was found in isolates CPBsZN-03-31, CPBsZN-04-34, and CPBsZN-06-36. The pathogen was recovered from inoculated oil palms in all cases. This study reveals the pathogenic association of Ganoderma zonatum with BSR in Colombia.

Reply to Paterson, R.R.M. Comment on "Castillo et al. Ganoderma zonatum Is the Causal Agent of Basal Stem Rot in Oil Palm in Colombia. J. Fungi 2022, 8, 230".

Reader Q: There was no morphological information provided for the isolated specimens, and so it is not known if they are even Ganoderma [...].