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of Phytopathology

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Morphological characterization, phylogeny and pathogenesis of Setophoma terrestris causing corky and pink roots of tomato (Solanum lycopersicum) in Sinaloa, Mexico

By Ana María López López, Juan Manuel Tovar Pedraza, Josefina León Félix, Raúl Allende Molar, Nelson Bernardi Lima, Isidro Márquez Zequera, Raymundo Saúl García Estrada*

* Corresponding Author. Email: - / Institution: Centro de Investigación en Alimentación y Desarrollo

Accepted: 28/January/2024 – Published: 13/February/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2309-5

Abstract Background/Objective. Tomato (Solanum lycopersicum) is one of Mexico’s main crops. In the years 2017 and 2018, symptoms of corky and pink roots were observed with an incidence of 10 to 20% in Culiacan, Sinaloa, Mexico. In the foliage, plants presented a generalized chlorosis, with stunted growth and senescence in the leaves. In the roots, brown and pink lesions were formed, as well as a corky texture. The objective of this study was to morphologically and molecularly characterize fungal isolates associated to corky and pink root in tomato orchards in Culiacan, Sinaloa, as well as to evaluate their pathogenicity.

Materials and Methods. Monoconidial isolates were obtained and they were identified as Setophoma terrestris, based on their morphological characteristics. To confirm the identity, the area of the internal transcribed spacers (ITS) of the rDNA was amplified and sequenced, along with a fragment of the gene 28S of the rRNA (LSU).

Results. Using the sequences obtained, a phylogenetic tree was created using the Bayesian Inference and it was found that the sequences were grouped with the ex–type sequences of Setophoma terrestris. The pathogenicity of the isolates was verified by inoculating mycelial discs into the root of 10 one-month-old tomato seedlings. The roots of the seedlings inoculated with PDA discs without mycelium served as a control. Thirty days after inoculation, corky and pink root symptoms appeared, whereas the roots of control plants remained healthy

Conclusion. According to the morphological characterization, the molecular identification and the pathogenicity tests, Setophoma terrestris was confirmed to be the causal agent of corky and pink root in agricultural tomato orchards in Culiacan, Sinaloa.

Keywords: Setophoma, fungus, tomato, bayesian inference, root disease

Figure 1. Location of the sites of recollection of plants with corky root symptoms in agricultural systems with tomato production in the valley of Culiacan, Sinaloa. Site 1 (24°42’56.58”N, 107°26’42.86”W), Site 2 (24°35’21.67”N, 107°24’56.50”W), Site 3 (24°46’2.77”N, 107°32’51.30”W), Site 4 (24°48’47.44”N, 107°39’26.19”W) and Site 5 24°32’34.07”N, 107°26’44.93”W)
Figure 1. Location of the sites of recollection of plants with corky root symptoms in agricultural systems with tomato production in the valley of Culiacan, Sinaloa. Site 1 (24°42’56.58”N, 107°26’42.86”W), Site 2 (24°35’21.67”N, 107°24’56.50”W), Site 3 (24°46’2.77”N, 107°32’51.30”W), Site 4 (24°48’47.44”N, 107°39’26.19”W) and Site 5 24°32’34.07”N, 107°26’44.93”W)
Figure 2. Symptoms of corky and pink roots in tomato. A–C) Chlorosis, deficient growth and senescence in plants. D–F) Dark brown lesions on the root, with swelling, a corky texture and a pink color
Figure 2. Symptoms of corky and pink roots in tomato. A–C) Chlorosis, deficient growth and senescence in plants. D–F) Dark brown lesions on the root, with swelling, a corky texture and a pink color
Figure 3. Colonies and asexual reproductive structures of <em>Setophoma terrestris</em>. A) Colony of S. terrestris in a V8A medium with 7 days of growth. B) Colony growth on the reverse of the dish. D) Pycnidium. D) Setae. E–F) Biguttulate conidia.
Figure 3. Colonies and asexual reproductive structures of Setophoma terrestris. A) Colony of S. terrestris in a V8A medium with 7 days of growth. B) Colony growth on the reverse of the dish. D) Pycnidium. D) Setae. E–F) Biguttulate conidia.
Figure 4. Bayesian Tree obtained with combined data from sequences ITS and LSU. The tree shows the phylogenetic relations of the Setophoma species. The Bayesian posterior probability values of over 0.70 are shown in the nodes. The species Pseudopyrenochaeta lycopersici was used as an external group and the scale bar indicates the number of expected changes per site.
Figure 4. Bayesian Tree obtained with combined data from sequences ITS and LSU. The tree shows the phylogenetic relations of the Setophoma species. The Bayesian posterior probability values of over 0.70 are shown in the nodes. The species Pseudopyrenochaeta lycopersici was used as an external group and the scale bar indicates the number of expected changes per site.
Figure 5. Pathogenicity tests in tomato plants. A–B) Tomato plants of the 8444 variety inoculated with S. terrestris and showing symptoms of yellowing. C) Corky root symptom 30 days after inoculation with S. terrestris. D) Colony obtained from the <em>in vitro</em> reisolation of S. terrestris.
Figure 5. Pathogenicity tests in tomato plants. A–B) Tomato plants of the 8444 variety inoculated with S. terrestris and showing symptoms of yellowing. C) Corky root symptom 30 days after inoculation with S. terrestris. D) Colony obtained from the in vitro reisolation of S. terrestris.
Table 1. Information of fungal isolates and GenBank accession numbers of Setophoma species used in the phylogeneti analysis.
Table 1. Information of fungal isolates and GenBank accession numbers of Setophoma species used in the phylogeneti analysis.
Table 2. Measurements of asexual structures in Setophoma terrestres isolates obtained from tomato plants.
Table 2. Measurements of asexual structures in Setophoma terrestres isolates obtained from tomato plants.