Use of Pseudomonas protegens to Control Root Rot Disease Caused by Boeremia exigua var. exigua in Industrial Chicory (Cichorium intybus var. sativum Bisch.).

Boeremia exigua var. exigua is a recurrent pathogen causing root rot in industrial chicory. Currently, there is no chemical or varietal control for this disease, and thus, management strategies need to be developed. This study determined the biocontrol effect of strains of Pseudomonas protegens bacteria with antimicrobial compounds on the fungus B. exigua var. exigua under in vitro, in vivo, and field conditions. In addition, root colonization by these bacteria was estimated by the phlD-specific PCR-based dilution end point assay. Eighteen isolates of Pseudomonas spp were evaluated, and the strains that showed the greatest in vitro inhibition of fungal mycelial growth (mm), Ca10A and ChB7, were selected. Inoculation with the strain ChB7 showed less severity (necrotic area) under in vivo conditions (root trials) compared with the control inoculated with the pathogen (p ≤ 0.05). The molecular analysis revealed that the root colonization of plants grown in pots was equal to or greater than 70%. Similar levels were observed in the field trials conducted at the Selva Negra and Canteras experimental stations (2015-2016 season), with values ranging from 85.7 to 70.5% and from 75.0 to 79.5%, respectively. Regarding yield (ton ha-1), values were higher in the treatments inoculated with strains Ca10A and ChB7 (p ≤ 0.05) at both experimental sites, while a lower incidence and severity of root rot were observed at Selva Negra. These results suggest that the Chilean strains of P. protegens are a promising tool for the control of root diseases in industrial chicory.

First report of Diplodia mutila causing wood necrosis in European hazelnut in Chile.

In Chile, the planted area of European hazelnut (Corylus avellana L.) reaches around 30,000 hectares, mainly concentrated in the central and southern area of the country where climate and soil provide a natural environment well suited to growing this species. Only a few diseases affect this nut tree in Chile. During the spring seasons in 2018 and 2020, European hazelnut plants (6 to 20% of incidence) exhibited wood necrosis and vascular discoloration of branches, with reduced growth, cankers and wilt branches, in orchards located in San Clemente and Curicó, Maule Region, Bulnes and El Carmen, Ñuble Region, Chile (36°45'-36°54' S; 71°03'-72°26' W). Symptomatic tissues were surface disinfected using a ~1% commercial sodium hypochlorite solution. Disinfected tissues were cut longitudinally, placed onto potato dextrose agar (PDA, Difco) plates, and incubated at 25 °C in the dark for 48 hours. Fungal hyphal tips were taken and placed on PDA medium. A fungal species was consistently isolated from these lignified tissues. The mycelium was initially translucent (turning white in appearance), while the mature mycelium was aerial, varying in color from pale to dark gray (Munsell color code: colony edge mycelium 6Y-6 4 / 5G and colony center mycelium B6-PB 7 / 5PB). The production of pycnidia and conidia was induced using pine needles in water agar medium and incubated in the dark for 10 days. Hyaline unicellular conidia of 25 ± 1.1 µm (range 23.9 to 26.1 µm) long and 11 ± 0.5 µm (Range 10.5 to 11.5 µm) wide (n = 50) were obtained from black pycnidia. Based on the cultural and morphological characteristics observed, the pathogen was identified as a possible species of the family Botryosphaeriaceae (20 isolates). Molecular techniques were used to identify the species of pathogen, and three isolates (F154, F199, and F167) were analyzed by using Multilocus sequence typing to confirm the identity of the pathogen. Genes ITS (internal transcribed spacer region), tef-1 (translation elongation factor 1-alpha) and ß-tub (ß-tubulin) were amplified using endpoint PCR, with primers ITS1/ITS4 (White et al., 1990), EF1-728F/EF1-986R (Carbone & Kohn, 1999) and Bt2a/Bt2b (Glass & Donaldson, 1995), respectively. The segments were sequenced using the same primers, deposited in Gen Bank, and the accession numbers for each isolate were OM993582, OM993583, ON003481 for ITS, ON054936, ON054938, ON054937 for tef1 and ON054939, ON054941, ON054940 for ß-tub, respectively. A phylogenetic tree was constructed using the maximum likelihood statistical method with the Tamura-Nei model based on a concatenated dataset of ITS region, tef1 and ß-tubulin gene using Mega-X, and the three Chilean isolates (F154, F199, and F167) formed a single clade with the reference isolates of Diplodia mutila (Fr.) Mont. BLAST algorithm analyses indicated 100% identity to D. mutila for ITS (accession NR_144906), for tef-1 (accession MK573559), and for ß-tubulin (accession MG952719). The pathogenicity of the three isolates was validated through Koch's postulates. For this purpose, a trial was established in 6-year-old European hazelnut plants cv. Tonda Di Giffoni. Ten healthy branches were individually inoculated using actively growing mycelial discs from each isolate, while a disc of PDA without fungus was used as a control. Holes of 5-mm diameter were inoculated, making sure the mycelium was in contact with the wood. Finally, the wounds were sealed with plastic film to prevent external contamination and improve humidity conditions. After 120 days, each branch was cut longitudinal-sectioned to verify the presence of wood necrosis which arose between 3.0 to 16.2 mm of length around the point of inoculation. No necrosis was observed in the control. To confirm pathogenicity, infected tissues were cut into small pieces with sterile knives and scalpels, and surface disinfected with a 1% sodium hypochlorite solution for 1 min. The disinfected tissues were placed on PDA medium and incubated at 25°C in the dark until fungal growth was observed. Hyphal tips were taken from the mycelia developed from the pieces of wood, and placed on PDA medium in order to obtain pure isolates. The pathogenicity of the D. mutila isolates F154 and F199 was observed in 100% of the inoculated branches, while isolate F167 showed symptoms in 85% of the branches. The reisolated strains showed similar mycelial growth and microscopic fungal structures to those observed in the isolates used for inoculation. This is the first report of D. mutila affecting European hazelnut in Chile. This fungus has been recently reported affecting hazelnut in Oregon, USA (Wiman et al., 2019), causing similar symptoms to those observed in our study. In addition, D. mutila has been reported infecting walnut in Chile (Diaz et al. 2018) and native forest trees, specifically Araucaria araucana in Chile (Besoain et al., 2017). The presence of D. mutila in commercial hazelnut orchards in Chile highlights the need for epidemiological studies in order to understand the characteristics and impact of this pathogen and, based on this, develop adequate phytosanitary programs for its control.

Kinetic modelling of ascorbic and dehydroascorbic acids concentrations in a model solution at different temperatures and oxygen contents.

The degradation kinetics of vitamin C (ascorbic and dehydroascorbic acids, AA and DHA) were determined under controlled conditions of temperature (50-90 °C) and oxygen concentrations in the gas phase (10-30% mol/mol) using a specific reactor. The degradation of vitamin C in malate buffer (20 mM, pH 3.8), mimetic of an apple puree, was assessed by sampling at regular intervals and spectrophotometric quantification of AA and DHA levels at 243 nm. The results showed that AA degradation increased with temperature and oxygen concentration, while DHA exhibited the behaviour of an intermediate species, appearing then disappearing. A kinetic model was successfully developed to simulate the experimental data by two first order consecutive reactions. The first one represented AA degradation as a function of temperature and concentration in dissolved oxygen, and the second reflected DHA degradation as a function of temperature only, both adequately following Arrhenius' law.

Spectrophotometric method for fast quantification of ascorbic acid and dehydroascorbic acid in simple matrix for kinetics measurements.

A simple, rapid and reliable method was developed for quantifying ascorbic (AA) and dehydroascorbic (DHAA) acids and validated in 20mM malate buffer (pH 3.8). It consists in a spectrophotometric measurement of AA, either directly on the solution added with metaphosphoric acid or after reduction of DHAA into AA by dithiothreitol. This method was developed with real time measurement of reactions kinetics in bulk reactors in mind, and was checked in terms of linearity, limits of detection and quantification, fidelity and accuracy. The linearity was found satisfactory on the range of 0-6.95mM with limits of detection and quantification of 0.236mM and 0.467mM, respectively. The method was found acceptable in terms of fidelity and accuracy with a coefficient of variation for repeatability and reproducibility below 6% for AA and below 15% for DHAA, and with a recovery range of 97-102% for AA and 88-112% for DHAA.