Comparative Performance of Fungicides and Biocontrol Products in the Management of Fusarium Wilt of Blackberry.

Fusarium wilt of blackberry (FWB) is an emerging disease caused by a Fusarium oxysporum species complex. More than 3,000 ha of blackberry (Rubus spp.) crops have been lost in Mexico since 2011. The objectives of this research were: to evaluate the sensitivity of pathogenic F. oxysporum isolates recovered from symptomatic blackberry plants to fungicides with different modes of action; to assess the potential of these fungicides and plant resistance inducers against FWB in the greenhouse; and to determine the effects of commercial biofungicides and two indigenous strains of Trichoderma spp. on the incidence of FWB. The EC50 values of the fungicides prochloraz, thiabendazole, azoxystrobin, thiophanate-methyl, difenoconazole, triflumizole, and potassium phosphite for six pathogenic F. oxysporum isolates were determined. In a separate experiment, the fungicides acibenzolar-s-methyl (ASM), potassium phosphite, and commercial biofungicides, as well as two soil microbial inoculants and two indigenous Trichoderma strains, were tested for protection against wilt development in blackberry plants in the greenhouse. Prochloraz showed an average sensitivity for EC50 of 0.01 µg ml-1 for the tested F. oxysporum isolates, followed by difenoconazole and thiabendazole. Prochloraz and ASM proved to be the most effective treatments in the greenhouse. In contrast, potassium phosphite was ineffective in both the in vitro and in vivo experiments. The soil bioinoculants MicroSoil, Baktillis, T. koningiopsis, and T. asperellum significantly reduced the incidence of disease in the greenhouse. These results provide evidence for the potential of the various tools as useful components of integrated FWB management in the field.

First report of Fusarium falciforme (FSSC 3+4) causing wilt disease of Phaseolus vulgaris in Mexico.

Bean (Phaseolus vulgaris) is the second most important crop in Mexico after corn due to the high consumption of beans in all regions of the country. In the winter (January 2016), bean plants showing wilting, root discoloration and necrosis were observed, with an incidence of approximately 30% in different fields (<1 ha) in Tecoanapa, Guerrero State, Mexico. Symptomatic fine roots (<2 mm) were cut into 0.5 cm long pieces, washed with tap-water, surface disinfected with 1.5% NaOCl for 3 min, and rinsed with sterile distilled water. Thirty-five pieces were placed on potato dextrose agar (PDA, Difco) and incubated at 25 ℃ for seven days. Then, single-spore isolates were obtained. Colonies on PDA showed abundant white aerial mycelium and a growth rate of 4.5 mm/day, and in reverse, colonies were white/pink with a brown centre. Microconidia were cylindrical to ellipsoid, aseptate, hyaline and 7.8-(6.0)-4.7 × 2.7-(2.1)-1.6 µm. On carnation leaf agar, macroconidia were 37.8-(29.4)-23.5 × 4.1-(3.5)-2.6 µm, hyaline, falcate, with slightly curved apexes, and 3-5 septa. Chlamydospores were round, intercalary, hyaline, single or in chains (Boot 1971). A representative strain (CSAEGRO-AyDi-Ef) was analyzed by PCR and the translation elongation factor 1-alpha (tef1) gene (GenBank accession number MK945757) was sequenced using the EF-1/EF-2 primers (O'Donnell 2000). FUSARIUM-ID (Geiser et al. 2004) analysis showed 100% similarity with the Fusarium solani species complex (FSSC 3+4) strain NRRL28562. In addition, Bayesian phylogenetic analysis placed this strain in the Fusarium falciforme clade. A pathogenicity test was performed by immersing healthy plant roots (cv. Negro Jamapa) in 200 mL of a conidial suspension (50×106 conidia mL-1) for 10 min, and then transplanting the plants into pots. Control plants were immersed in sterile distilled water. Similar symptoms as those in the field were observed at 10 days after inoculation, and the controls were healthy. The fungus was reisolated from infected plants and showed the same morphology and tef1 sequence as the original isolate, fulfilling Koch's postulates. Recently, F. falciforme was reported to cause wilting of P. vulgaris in Cuba (Duarte et al. 2019); however, this is the first report of F. falciforme (FSSC 3+4) causing wilt disease of P. vulgaris in Mexico. This species was previously reported in Mexico affecting onion (Tirado-Ramírez et al. 2018), papaya, tomato (Vega-Gutiérrez et al. 2019a, b), and maize (Douriet-Angulo et al. 2019), suggesting an ample host range in the country.

An Emerging Strawberry Fungal Disease Associated with Root Rot, Crown Rot and Leaf Spot Caused by Neopestalotiopsis rosae in Mexico.

In the 2017 strawberry season, several transplant losses reaching 50% were observed in Zamora, Michoacán Valley, Mexico, due to a new fungal disease associated with root rot, crown rot, and leaf spot. In this year the disease appeared consistently and increased in the following seasons, becoming a concern among strawberry growers. Thus, the aim of this research was to determine the etiology of the disease and to determine the in vitro effect of fungicides on mycelial growth of the pathogen. Fungal isolates were obtained from symptomatic strawberry plants of the cultivars 'Albion' and 'Festival' and were processed to obtain monoconidial isolates. Detailed morphological analysis was conducted. Concatenated phylogenetic reconstruction was conducted by amplifying and sequencing the translation elongation factor 1 α, ß-tubulin partial gene, and the internal transcribed spacer region of rDNA. Pathogenicity tests involving inoculation of leaves and crowns reproduced the same symptoms as those observed in the field, fulfilling Koch's postulates. Morphology and phylogenetic reconstruction indicated that the causal agent of the described symptoms was Neopestalotiopsis rosae, marking the first report anywhere in the world of this species infecting strawberry. N. rosae was sensitive to cyprodinil + fludioxonil, captan, iprodione, difenoconazole, and prochloraz.

Conventional and qPCR reveals the presence of 'Candidatus Liberibacter solanacearum' haplotypes A, and B in Physalis philadelphica plant, seed, and Βactericera cockerelli psyllids, with the assignment of a new haplotype H in Convolvulaceae.

The husk tomato (Physalis philadelphica Lam.) is an important Solanaceae native to Mesoamerica that is grown for its green fruit used as an important ingredient in domestic and international cuisine. Nevertheless, husk tomato plants with symptoms resembling those caused by 'Candidatus Liberibacter solanacearum' (CLso) have been observed during the last decade in plantations located in the State of Mexico, Michoacan and Sinaloa in Mexico. These areas are located near other solanaceous crops where Bactericera cockerelli the well-known psyllid transmitter of CLso is frequently present. Thus, the goal of this study was to determine if CLso haplotypes are present in husk tomato varieties in commercial fields in Mexico. From 2015 to 2016, plants and fruit showing evident symptoms of CLso infection, as well as psyllids were collected in these states and assayed by PCR for CLso using primer sets OA2/OI2c and LpFrag 1-25F/427R. Phylogenetic reconstruction was performed with Bayesian analysis and maximum likelihood methods using amplicon sequences obtained in this work along with those deposited in the GenBank database corresponding to the CLso detected in Solanaceae, Apiaceae, and Convolvulaceae host families. In addition, all the sequences were subjected to haplotype determination through an analysis of DNA polymorphisms using the DnaSP software. Furthermore, quantitative PCR (qPCR) was performed using CLso-specific primers and probes. Phylogenetic reconstruction and qPCR confirmed the presence of CLso in plants, seeds and insect-vectors, and CLso sequences from plants and seeds completely matched haplotype B, whereas CLso haplotypes A and B were detected in B. cockerelli psyllids. Polymorphism analysis identified a novel Convolvulaceae-associated CLso haplotype, which was named haplotype H. The results of this study will enable the dissemination of infected seeds to new husk tomato production areas to be avoided.

Colletotrichum fructicola, a Member of Colletotrichum gloeosporioides sensu lato, is the Causal Agent of Anthracnose and Soft Rot in Avocado Fruits cv. "Hass".

The filamentous Ascomycota Colletotrichum gloeosporioides sensu lato is a fungus that has been reported worldwide as a causal agent of anthracnose disease in avocado and other crops. In Mexico, this species affects fruits from an early stage of development in the orchard until the post-harvest stage. Although fungicides are continuously applied to control Colletotrichum species, pericarp cankers and soft rot mesocarp in fruits are still frequently observed. Considering the lack of a precise description of the causative agent, the aim of the current study was to determine the pathogens involved in this symptomatology. Twenty-four isolates were consistently obtained from the pericarp of avocado fruits cv. "Hass" collected in the central avocado-producing area of Mexico. Morphological features such as colony growth, conidia size, and mycelial appressorium were assessed. Bayesian multilocus phylogenetic analyses were performed using amplified sequences of the internal transcribed spacer region of the nuclear ribosomal DNA; actin, chitin synthase, glyceraldehyde-3-phosphate dehydrogenase partial genes; and APn2-Mat1-2 intergenic spacer and mating type Mat1-2 partial gene from the nine selected isolates. In addition, fruits were inoculated with a conidial suspension and reproducible symptoms confirmed the presence of Colletotrichum fructicola in this area. This pathogenic species can now be added to those previously reported in the country, such as C. acutatum, C. boninense, C. godetiae, C. gloeosporioides, and C. karstii. Disease management programs to reduce the incidence of anthracnose should include C. fructicola to determine its response to fungicides that are routinely applied, considering that the appearance of new species is affecting the commercial quality of the fruits and shifting the original population structure.