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by Víctor Manuel Rodríguez Romero, Ramón Villanueva Arce, Enrique Durán Páramo
Accepted: 05/June/2024 – Published: 20/June/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2405-3
Abstract Background / Objetive. Nejayote is an alkaline agroindustrial waste that is generated from the nixtamalization process of corn. The purpose of this work was to demonstrate that nejayote can be used as a culture medium for the growth of Pseudomonas fluorescens NR113647 and to produce metabolites with antifungal activity for the sustainable management of Aspergillus niger, Botrytis cinerea and Fusarium solani.
Materials and Methods. Culture media were formulated with nejayote and nejayote with glycerol, with pH 6 and 12. The bacterial biomass was separated by centrifugation and filtration and the antifungal capacity of the extracts against A. niger, B. cinerea and F. solani was determined. The determination of the metabolites present in the extracts was carried out. P. fluorescens NR113647 was able to grow on all media.
Results. The extracts from nejayote at pH 12 showed inhibition of the growth of all the fungi evaluated; at least five metabolites produced by P. fluorescens NR113647 and involved in the biocontrol of phytopathogens were identified.
Conclusion. Nejayote can be used as a culture medium for P. fluorescens NR113647, to produce biomass and secondary metabolites with antifungal capacity; in addition, nejayote could be used for the cultivation of other microorganisms.
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Figure 1. Identification of the production of hydrogen cyanide in a Petri dish. Negative control of distilled water (A), extracts free of P. fluorescens NR113647 cells in a KB6 medium (B) and extracts free of P. fluorescens NR113647 cells in a N12 medium (C).
Figure 2. Identification of siderophores, Petri dish with distilled water as a control (A) and extracts free of P. fluorescens NR113647 cells (B) (Trejo-Raya et al., 2021) and extracts free of P. fluorescens NR113647 cells in a N12 medium (C).
Table 1. Evaluation of the growth of P. fluorescens NR113647 and pH values of the different treatments after 72 h of incubation
Table 2. Evaluation of the antifungal effect of the extracts obtained from P. fluorescens NR113647, on the mycelial growth and the inhibition of Fusarium solani, Botrytis cinerea and Aspergillus niger.
Table 3. Retention factors of the P. fluorescens NR113647 extracts obtained from treatment N12, comparison against standard compounds
by William Villalobos Muller, Laura Garita Salazar, Ana María Conejo Salazar, Izayana Sandoval Carvajal, Mauricio Montero Astúa, Lisela Moreira Carmona
Accepted: 05/June/2024 – Published: 20/June/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2403-1
Abstract Background/Objective. Bocconia frutescens (Papaveraceae) is a small tree distributed naturally from Mexico to Argentina and the Caribbean Bassin. Bocconia trees showing symptoms resembling phytoplasmas infection, such as little leaves and witches´-broom, were found in Cartago province, Costa Rica. Detection and identification of the potential phytoplasmas associated with B. frutescens little leaf symptoms was the objective out of this study.
Materials and Methods. Evaluation of leaves tissue using transmission electron microscopy (TEM), nested PCR using universal and specific primers to amplify phytoplasmas 16S rRNA and secA genes. Nucleotidic sequences (Sanger method) were obtained from amplicons, and used for BLASTn, phylogenetic analyses, and in silico RFLP’s.
Results. Presence of phytoplasmas into phloem tissue, only in symptomatic trees, was evidenced by TEM. Comparison of partial sequences (16Sr and secA genes) by BLASTn, in silico RFLP´s and phylogenetic analyses, showed the occurrence of a ´Candidatus Phytoplasma pruni´ related strain in the samples evaluated.
Conclusion. Phytoplasmas were found only in the symptomatic B. frutescens trees evaluated. The phytoplasmas were identified as a ´Ca. Phytoplasma pruni´ related strain. This is the first report of B. frutescens as a natural host of ´Ca. Phytoplasma pruni´.
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Figure 1. Bocconia frutescens (Papaveraceae) trees showing symptoms reminiscent of phytoplasmas infection, observed in Cartago province, Costa Rica; A) witches’-broom and bunches of little leaves observed in some branches; B) Witches’- broom, defoliation, and die-back; C) Detail of axillar proliferation with leaves reduced in size.
Figure 2. (A) Pleomorphic phytoplasmas bodies (») found inside phloem of Bocconia frutescens trees with little leaves and witches’ broom symptoms observed in Cartago province, Costa Rica. CW = cell wall. (B and C) Profiles of virtual RFLPs obtained at iPhyClassifier to 16Sr F2/R2n fragment of phytoplasmas associated to B. frutescens little leaf (BfLL, GenBank Acc. No. PP353584) using BstUI (C) and HpaII (D). Molecular weight (MW) fragment sizes (bp): 1353, 1078, 872, 603, 310, 281, 271, 234, 194, 118, 72
Figure 3. Dendrogram obtained from phylogenetic analysis using Maximum Parsimony method of partial 16S rRNA gene sequences from Bocconia frutescens little leaf (BfLL) phytoplasma, 29 sequences of 16SrIII group´s strains, seven ‘Ca. Phytoplasma species´ and Acholeplasma laidlawii as outgroup. The bootstrap test selected was 1000 replicates. GenBank accession number of every sequence is shown in parentheses. BfLL phytoplasma is displayed in bold. * = tentatively new subgroups
Figure 4. Dendrogram obtained from phylogenetic analysis with Maximum Parsimony using partial secA gene sequences from Bocconia frutescens little leaf associated phytoplasma, ten sequences of secA from different 16SrIII subgroups, ‘Ca. Phytoplasma trifolii´ and Bacilus subtilis (outgroup). The bootstrap test selected was 1000 replicates. GenBank accession number of every sequence is shown in parentheses. * = tentatively new subgroup.
Table 1. Localities at Cartago province, Costa Rica, where trees of Bocconia frutescens were observed with little leaf symptoms associated with phytoplasmas.
Table 2. Data about oligonucleotides (primers) and thermocycle profiles herein used for the detection of phytoplasmas genes 16S rRNA and secA translocase gene.
Table 3. Unique oligonucleotide sequence regions (UOSR) in the 16S rRNA gene of ‘Candidatus Phytoplasma pruni’ rrnA (JQ044393, Davis et al., 2013) compared to 16Sr sequence of BfLL associated phytoplasma (PP353584). Position in the respective sequence is shown in parenthesis, every nucleotide corresponding to a SNP is displayed in standard DNA nucleotides color, bold font and underlined.
Identification of phytoplasmas associated with Bunchy Top disease of papaya in Colima, Mexico
by Pedro Valadez Ramírez, Daniel Leobardo Ochoa Martínez, Guadalupe Valdovinos Martínez, Edith Blanco Rodríguez, Sergio Aranda Ocampo, Candelario Ortega Acosta, Marco Tulio Buenrostro Nava, Jetzajary Ayerim Rodríguez Barajas, Luis Rafael De la Torre Velázquez, Carlos Luis Leopardi Verde
Accepted: 19/May/2024 – Published: 18/June/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2403-2
Abstract Background/Objective. Phytoplasmas, rickettsiae and viruses have been detected in papaya plants with Bunchy Top disease (BT). In 2019, papaya plants with BT- like symptoms were observed in agroecosystems of Colima, Mexico. In order to determine the BT-associated phytoplasmas species or subgroups, asymptomatic and symptomatic plants were collected from papaya agroecosystems in four papaya producer municipalities, as well as papaya-associated weeds and insects.
Materials and Methods. Phytoplasma detection and identification was conducted by PCR, sequencing and phylogenetics of translocase subunit SecA (secA) and 16S ribosomal RNA (16Sr) genes, and PCR-RFLPs in vitro and in silico for 16Sr gene.
Results. In papaya, phytoplasma groups 16SrI (subgroup AF), 16SrX, and 16SrXIII were identified in 2.08% (4 out of 192) symptomatic samples. The results of RFLPs in silico analysis showing the presence of 16SrX and 16SrXIII (sub)groups. In papaya-associated weeds and insects, phytoplasmas of group 16SrI (subgroups AF and B) were identified in 1.7% (3 out of 174) and 1.1% (2 out of 185) evaluated samples, respectively. Phytoplasma-carrying weeds were Amaranthus palmeri and Echinochloa colona; positive insects were Micrutalis calva and Balclutha mexicana.
Conclusion. It is the first time that phytoplasmas 16SrI-AF, 16SrX y 16SrXIII are associated with Bunchy Top disease of papaya in agroecosystems from Colima, Mexico. Phytoplasmas 16SrX y 16SrXIII are first reported in papaya plants at the world level and in Mexico, respectively. Phytoplasma-carrying weeds and insects are new records as natural reservoirs and potential vectors.
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Figure 1. Detection of phytoplasmas in agroecosystems papaya with Bunchy Top disease in Colima, Mexico. A) Papaya plants showing stems with shortened internodes and yellow, chlorotic leaves, positive to phytoplasmas. B) in vitro RFLPs profiles of gene 16Sr (primers R16F2n/R16R2) of the phytoplasmas under study. Lanes 1-4: samples 1S-4S- papaya, Lanes 5-6: samples 5S-6S-Amaranthus palmeri; Lane 7: sample 7S-Echinochloa colona; Lane 8: sample 8S-Micrutalis calva; and Lane 9: sample 9S-Balclutha mexicana. The DNA was digested with 10 U of every enzyme and the products were separated by electrophoresis in 3% (w/v) agarose gels in 1×TAE buffer. Lane M: 1 kb plus molecular weight marker (Thermo Scientific, EUA).
Figure 2. in silico RFLPs profiles of gene 16Sr of the phytoplasmas under study, generated with iPhyClassifier with 17 restriction enzymes. A) sample 1S-papaya; B) sample 2S-papaya; C) sample 3S-papaya; D) sample 4S-papaya, E) sample 5S-Amaranthus palmeri; F) sample 6S-Amaranthus palmeri; G) sample 7S-Echinochloa colona; H) sample 8S-Micrutalis calva; I) sample 9S-Balclutha mexicana. Lanes MW: φX174 DNA digested with Hae III
Figure 3. Phylogenetic trees of the secA (A) and 16Sr (B) trees obtained using the neighbor-joining method of 16Sr groups of phytoplasmas identified in papaya agroecosystems in Colima, Mexico (black circles) and from phytoplasma groups from other parts of the world. Accession number are shown in parentheses. Samples 1S-4S: papaya, samples 5S-6S: Amaranthus palmeri, sample 7S: Echinochloa colona, sample 8S: Micrutalis calva, sample 9S: Balclutha mexicana. The gene sequence of secA of Bacillus subtilis and the 16Sr gene sequence of Acholeplasma laidlawii were used as outgroups. In each phylogeny, bootstrap values (from 1000 replicates, greater than 70%) are shown on the branches. The scale bar indicates the number of nucleotide substitutions per site
Table 1. Detection of phytoplasmas in papaya (Carica papaya), weeds and insects associated with the crop in Colima, Mexico, in November and December of 2019.
Table 2. Phytoplasmas identified in papaya, weeds and insects associated with the crop in Colima, Mexico, in November-December of 2019.
by María Emilia Belingheri Lagunes, Rosario Medel Ortiz, Alejandro Salinas Castro, Dora Trejo Aguilar
Accepted: 18/January/2024 – Published: 07/June/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2401-1
Abstract Background/Objective. The objective of this work was to evaluate the in vitro antagonistic capacity of a strain of Clonostachys sp. against five species of fungi associated with diseases in economically important crops.
Materials and Methods. Five fungal species associated with crop diseases were tested: Alternaria alternata, Colletotrichum kahawae, C. musae, Fusarium oxysporum and F. solani. Dual cultures were performed with five replicates plus controls. Growth was recorded every 24 hours, until 360 hours were completed. Interactions were determined, the degree of antagonism and the percentage of colonization was calculated. Statistical analyses were performed with a generalized linear model (GLM).
Results. All species evaluated showed antagonism of the overgrowth type. The degree of antagonism was classified into three classes, with class two being present in three of the species. The percentage of colonization was 100% at 216 h for three of the species and 264 h for the other two. There was no significant difference in the percentage of colonization (p =0.0073), but there was a significant difference in the time of invasion (p< 0.0001).
Conclusion. Dual assays to test the antagonistic effect in vitro form the basis for the selection of candidates for biological control of fungi.
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Figure 1. in vitro antagonism of Clonostachys sp. (Csp.) against Alternaria alternata (Aa). A: After 24 hours of evaluation. B. 120 hours of evaluation. C. 216 hours of evaluation. D. 360 hours of evaluation.
Figure 2. in vitro antagonism of Clonostachys sp. (Csp.) against Colletotrichum kahawae (Ck) and Colletotrichum musae (Cm). A-D) Colletotrichum kahawae (Ck). A: 24 hours after evaluation. B: 192 hours of evaluation. C: 360 hours of evaluation. D: reverse Petri dish at 360 hours of evaluation. E-H) Colletotrichum musae (Cm) against Clonostachys sp. (Csp.). E: 24 hours of evaluation. F: 192 hours of evaluation. G: 360 hours of evaluation. H: Conidiophores of Clonostachys sp. growing on acervuli of C. musae
Figure 2. in vitro antagonism of Clonostachys sp. against Fusarium spp. A-D) Fusarium solani (Fs) against Clonostachys sp. (Csp.) A: after 24 hours of evaluation. B: at 96 hours of evaluation. C: at 360 hours of evaluation. D: masses of aqueous conidiophores at the margin of Clonostachys sp. E-H) Fusarium oxysporum (Fo) against Clonostachys sp. (Csp.) E: 24 hours of evaluation. F: 144 hours of evaluation. G: 192 hours of evaluation. H: 360 hours of evaluation
Table 1. Qualitative scale of the degree of antagonism of Clonostachys sp. and the evaluated fungi associated to diseases.
Table 2. Percentage of growth of Clonostachys sp. against the fungi.
by Alejo Jairo Cristóbal, José María Tun Suárez, Arturo Reyes Ramírez, Alberto Uc Várguez, Silvia Edith García Díaz
Accepted: 01/July/2024 – Published: 12/July/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2405-5
Abstract Background/Objective. In the state of Yucatan, Mexico, 10 million forest plants were produced in the last five years for various conservation and restoration actions. The main limitations in the production of these plants in nursery are disease induced by the genus Fusarium spp., that cause stem and root rots and plant production losses of up to 50%. The objective of the work was to identify the causal agent associated with stem and root rot and necrosis of cedar (Cedrela odorata) and mahogany (Swietenia macrophylla) and their in vitro sensitivity to conventional fungicides.
Materials and Methods. C. odorata and S. macrophylla plants were collected at three and six weeks of germination, respectively, with symptoms of necrosis and rot indicated; from where five fungal isolates were obtained and morphologically and molecularly identified. The Minimum Inhibitory Concentration (MIC) of spores and the Minimum Lethal Concentration (MLC) of six conventional fungicides of recurrent application in the region (Prochloraz, Carbendazim, Benomyl, Fosetyl Al, Captan and Mancozeb) were determined in vitro by the microdilution method and validate their effectiveness and viability in the management of this problematic.
Results. The morphology and molecular sequences of the isolates were similar to the reported for Fusarium solani. The MIC of F. solani spores for Prochloraz, Carbendazim, Benomyl, Captan and Mancozeb were 2.44. 11.38, 14.06, 7.81 and 7.81 ppm, respectively; Fosetyl Al, did not inhibit spore germination normal mycelial growth of the fungus was observed at the concentration evaluated.
Conclusion. Prochloraz and Mancozeb had the lowest MLC with 2.44 and 7.81 ppm, respectively.
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Figure 1. Plants with symptoms of necrosis and rot in the stem and root. A, B, and C) Cedrela odorata plants. D, E, and F) Swietenia macrophylla plants
Figure 2. A and D) View of 14-day-old Fusarium solani isolated from Cedrela odorata and Swietenia macrophylla, B) Septate mycelium and microconidia of F. solani, C) Macroconidia (3-4 septa) and microconidia (0-1 septum) of F. solani observed at 100X magnification, E) Macroconidia and microconidia observed at 40X magnification, and F) Sporodochia
Figure 3. Fungicidal effect of Prochloraz and Mancozeb on the spore solution of Fusarium solani obtained from the microdilution plate after two days of evaluation. A) Distribution in Petri dishes with PDA medium of five MIC obtained from Prochloraz, B and C) No mycelial growth of F. solani in the MIC of Prochloraz evaluated after 24 and 48 h, D) Distribution in Petri dishes with PDA medium of five MIC obtained from Mancozeb, E and F) No mycelial growth of F. solani in the MIC of Mancozeb evaluated after 24 and 48 h
Table 1. Conventional fungicides evaluated for their effect on spore germination and mycelial growth of Fusarium solani isolated from Cedrela odorata and Swietenia macrophylla.
Table 2. Minimum inhibitory concentration (MIC) and minimum lethal concentration (MLC) of conventional fungicides against Fusarium solani isolated from Cedrela odorata and Swietenia macrophylla
by Miguel Ángel Ruíz González, Miguel Ángel Serrato Cruz, Ernestina Valadez Moctezuma, Roney Solano Vidal
Accepted: 25/June/2024 – Published: 09/July/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2401-5
Abstract Background/Objective. Aromatic plants contain chemical compounds with potential to formulate antifungal products. The objective of this study was to characterize the chemical composition in hydrolates of Tagetes species and to evaluate their effect in vitro and in vivo against disease-associated fungi in strawberry.
Materials and Methods. The hydrolates of T. coronopifolia, T. minuta, T. parryi and T. terniflora were analyzed by gas chromatography coupled to a mass spectrometry. Hydrolates at 100, 75, 50 and 25 % and Promyl commercial fungicides were evaluated in vitro against Botrytis cinerea, Fusarium oxysporum, Rhizoctonia solani and Ridomil Gold against Phytophthora capsici. In the in vivo evaluation, strawberry plants sprayed with the hydrolates and 24 h later the plants were inoculated with 1 x 106 spore suspension. Data were analyzed by analysis of variance and Turkey’s means test (p ≤ 0.05).
Results. Monoterpenes were the major compounds in the four Tagetes species. T. parryi hydrolate in vitro totally inhibited the growth of B. cinerea being effective as a preventive treatment in the in vivo evaluation. F. oxysporum, P. capsici and R. solani were less susceptible to all the hydrolats.
Conclusion. T. parryi hydrolate can be applied as a preventative against B. cinerea on strawberry plants
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Figure 1. Tagetes parryi (Tp), T. terniflora (Tt), T. coronopifolia, (Tc) and T. minuta (Tm) hydrosol chromatograms, showing the peaks of the compounds identified
Figure 2. Incidence of B. cinerea, R. solani, F. oxysporum and P. capsici in strawberry fruits (A) and flowers (B) three days after their inoculation in control (TO) plants and treated with 100% Tagetes coronopifolia (H100C), T. minuta (H100M), T. parryi (H100P) T. terniflora hydrolates (H100T)
Table 1. Relative abundance (%) and Kovats indices (KI) ± standard deviation of chemical compounds found in Tagetes coronopifolia, T. minuta, T. parryi and T. terniflora hydrolates analyzed using GC/MSD
Table 2. Percentage of in vitro inhibition of fungus mycelia after applying Tagetes species hydrolates
Fungal causal agents of the Black Spot of the cactus (Opuntia ficus-indica) in Colima, Mexico
by Zoila Lizbeth Chavarría Cervera, Andrés Quezada Salinas, Pedro Valadez Ramírez, Wilberth Chan Cupul, Jesús Enrique Castrejón Antonio, Juan Carlos Sánchez Rangel
Accepted: 06/March/2024 – Published: 02/April/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2401-2
Abstract Background/Objective. The prickly pear cactus (Opuntia ficus-indica) holds significant economic, social, and cultural importance in Mexico. However, it is recurrently affected by Black Spot disease (BS), caused by various phytopathogenic fungi. Identifying the causal agents of BS in commercial prickly pear crops is crucial for efficient agronomic management of the disease. The objective of this study was to identify the phytopathogenic fungi responsible for BS in prickly pear plantations in the Colima state, Mexico.
Materials and Methods. Fifty cladodes from 50 plants exhibiting BS symptoms were collected from commercial plantations in Colima. The pathogenicity of the isolated fungi was verified using Koch’s postulates, and those causing the most severe BS symptoms were molecularly identified.
Results. Thirty-five fungi were isolated from plants with BS symptoms, of which 20 exhibited distinct mycelial growth. Only six fungi induced BS symptoms; three of them were responsible for severe symptoms in cladodes: Alternaria alternata, Corynespora cassiicola, and Neoscytalidium dimidiatum.
Conclusion. BS is caused by various phytopathogenic fungi, but this is the first report of C. cassiicola and N. dimidiatum as causal agents of BS in prickly pear cactus
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Figure 1. Plants and cladodes with symptoms of Black Spot in vegetable prickly pear cactus (O. ficus-indica) crops in various plantations in Colima state, Mexico. A) El Espinal, B) Agua Dulce, C) Las Guásimas, D) Juluapan
Figure 2. Fungi isolated from prickly pear cactus cladodes showing symptoms of Black Spot. The isolates are deposited in the mycological collection of the Faculty of Biological and Agricultural Sciences at the University of Colima for subsequent morphological and molecular characterization.
Figure 3. Fungi isolated from cladodes with Black Spot symptoms that induced severe lesions in the pathogenicity test. Growth on PDA of Alternaria alternata (obverse, A; reverse B) and symptoms induced on the cladode (E), Corynespora cassiicola (D, E, F), and Neoscytalidium dimidiatum (G, H, I).
Armillaria gallica associated with avocado root rot in Michoacán
by Jeny Michua Cedillo, Daniel Téliz Cedillo, Salvador Ochoa Ascencio, María del Pilar Rodríguez , Alejandro Alarcón , Carlos de León , Gerardo Vázquez Marrufo
Accepted: 02/March/2024 – Published: 21/March/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2307-7
Abstract Aims and background. Root rot and the death of avocado trees related to Armillaria is an emerging disease with a high economic impact in orchards established in previously forested areas of Michoacán. Nowadays, the species related with typical symptoms of wilting, yellowing, excessive fruit production and subcortical mycelia in the roots is unknown. The aim of this investigation was to molecularly characterize the species of Armillaria associated to avocado root rot.
Materials and Methods. For the morphological and molecular characterization, 60 root simples from trees found in three commercial orchards with a putative presence of Armillaria were processed in a malt-agar extract. The DNA of purified isolations were amplified by PCR with genes RPB2 and TEF α-1. The sequences were aligned using MAFFT and the phylogenies were constructed using the maximum likelihood algorithm in IQ-TREE.
Results. Two species were consistently identified: A. gallica (20%) with a 100% homology, and A. mexicana (25%), with 98%. Another species that represented 55% of the isolations was not aligned with any group. Morphologically, the A. gallica basidiocarps coincide with the characteristics of this species.
Conclusion. This is the first report on A. gallica associated to avocado root rot in Michoacán
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Figure 1. Armillaria morphotypes taken from avocado orchards in different municipal areas of the avocado belt in Michoacán. A. Front, B. Reverse.
Figure 2. Armillaria gallica basidiocarps gathered in Charapan, Michoacán. A. Mature Armillaria gallica basidiocarps (yellow cap with scales); B. Immature gray A. gallica basidiocarps with scales; C. Single basidiocarp with a single rhizomorph on the base.
Figure 3. Phylogenetic analysis with Armillaria species sequences from avocado and from the GenBank amplified with the gene TEF α-1. Isolate MICH29 was directly grouped with the species Armillaria gallica. Strains MICH32 and MICH32R are broadly related to Armillaria mexicana, whereas MICH21 was grouped between the clade of A. mellea and A. mexicana
Figure 4. Phylogenetic analysis of sequences of Armillaria species from avocado and the GenBank amplified with gene RPB2. Strain MICH29 and MICH29R are grouped directly with the species Armillaria gallica, while MICH21 is related to A. mellea.
Accepted: 21/March/2024 – Published: 11/April/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2307-3
Abstract Diaphorina citri is the main vector of Candidatus Liberibacter asiaticus (CLas), the causative agent of HLB, the most devastating citrus disease. Although the importance of biological control is recognized, insecticides are the main control tool used. Its use in citrus should be cautious, as it could interfere with the biocontrol of exotic pests already present. Diaphorina citri has a wide range of natural enemies; however, only the parasitoid Tamarixia radiata and some species of entomopathogenic fungi are used inundatively. Although the main predators of the vector occur naturally, few studies address their conservation in situ. This review supports the idea that the conservation of natural enemies should be the basis of the integrated management of D. citri and CLas. The conservation of alternate hosts, the inclusion of nectar plants, in situ conservation of parasitoids, and the autodissemination of entomopathogenic fungi are proposed. Studies carried out on conservation of natural enemies of D. citri and related pests, their probable impact on the disease, and prospects for implementation in Mexico are analyzed and discussed. The proposed strategies could enhance not only the biological control of D. citri-CLas, but also the autoregulation of citrus pests in general.
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Figure 1. Epidemiological System defined by the interaction of factors that determine an epidemic process: pest species, entomopathogen, predator, and parasitoid, crop, agronomic management, climate, and any other specific factor (ni), all of which operate at different spatial-temporal levels (Adapted from Mora-Aguilera et al., 2017).
Figure 2. Aphis nerii on Asclepias curassavica and some associated natural enemies. A) Pseudodorus clavatus, B)Cycloneda sanguinea, C) Adult of Oligota sp., D) Adult of Chamaemyiidae, E) Mummies and adults ofLyciphlebus testaceipes
Figure 3. Different types of mesh evaluated in the selective emergence of Tamarixia triozae, parasitoid of Bactericera cockerelli as a model to be implemented with D. citri and its parasitoid. A) 700 x 700 μm, B) 700 x 900 μm, and C) 500 μm mesh.
Figure 4. Phytosanitary trophic system in two citrus species (Persian lime and sweet orange) and the lemon grass M. paniculata, which are differentially infested with two pest-vector species (D.citri and T. citricida) and two pathogens (Citrus tristeza virus and Candidatus Liberibacterasiaticus). Taken from Mora et al. (2017).
Table 1. Natural enemies associated with D. citri in citrus orchards in Mexico
Iris yellow spot orthotospovirus pathosystem, virus host and vector (Thrips tabaci)
by Norma Ávila Alistac, Erika J. Zamora Macorra, Héctor Lozoya Saldaña
Accepted: 10/March/2024 – Published: 10/March/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2310-8
Abstract Iris yellow spot Orthotospovirus (IYSV) causes serious problems in the onion (Allium cepa) crop and is widely distributed in the producing areas of the country. In Mexico it was reported in 2010 as “yellow spot” on onion and other members of the genus Allium. Its main vector is Thrips tabaci, which causes direct damage by feeding and by being a vector of other viruses such as Tomato spotted wilt Orthotospovirus and Impatiens necrotic spot Orthotospovirus. Knowledge of the pathosystem of IYSV - Thrips tabaci - Allium cepa - weeds can contribute to an integrated management and awareness of pesticide use. The versatility of IYSV to infect more than 60 plant species (>20 families), most of which are present in Mexico, coupled with the wide host range of the vector, makes the interaction complex and leads to a better understanding of the diversity of alternate hosts of the vector and/or IYSV. At present, information on weed hosts of IYSV and the vector is limited, but their knowledge will provide a greater understanding of the disease. It is important to have a comprehensive knowledge of the virus, main host, alternate hosts, and vector in the country, in order to channel future research to counteract this problem and minimize losses caused by IYSV in the onion crop mainly
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Figure 1. Representation of the segmented organization of the Iris yellow spot Orthotospovirus RNA genome (L, M and S). Modified from Bag et al. (2015)
Figure 2. A and B) symptoms associated with the Iris yellow spot Orthotospovirus infection, consisting of pale straw- colored chlorotic lesions with an elongated shape. C and D) pale straw-colored chlorotic lesions with a green island in the center of the lesion E-G) presence of large T. tabaci populations (immature and adult) in the onion crop.
Figure 3. Weeds interacting inside and outside of the onion (Allium cepa) crop. A) Parthenium weed (Parthenium hysterophorus); B) Purslane (Portulaca oleracea); C) Pineland threesed mercury (Acalypha ostryifolia); D) Mexican sunflower (Tithonia tubiformis) on the edge of an onion crop.
Figure 4. Epidemiological system of a viral pathosystem focused on Iris yellow spot Orthotospovirus (based on and modified from Madden et al., 2000). Notes used: v(t)= Total fertility rate of the insect population per day within the crop. Ґ= Virus incubation time within the vector. q= Probability that the offspring of the vector will be viruliferous. β= Plant mortality and recovery rate (replanting). α= Insect mortality and birth rate. ɸb= (Plants visited by insects per day) (Probability that the viruliferous insect inoculates the virus in a plant per visit). 1/k1= Time taken for the vector to inoculate the plant. 1/k2= Virus latency period in the plant. 1/k3= Infectious period of the virus in the plant. ɸT= (Plants visited by insects per day) (Time taken for the insect to sample the plant in one visit). Ex= Rate of emigration of virus-free insects. Ix= Rate of emigration of virus-free insects. Ey= Rate of emigration of latent insects. Ez= Rate of emigration of infective insects. Iy= Rate of emigration of latent insects. Iz= Rate of immigration of infective insects. 1/λ = Vector acquisition time. ɸa= (Plants visited by insects per day) (Probability that an insect will acquire the virus with a single visit to the infected plant). 1/ƞ= Time taken for the virus to transition from latent to infective within the vector (latency period). For further information, refer to Madden et al. (2000)
Table 1. Range of Iris yellow spot Orthotospovirus hosts