Diyanira Castillo-Novales

Species within the genus Phytopythium have recently been recognized as significant soilborne pathogens impacting various crops globally. However, their occurrence and pathogenicity in sweet cherry (Prunus avium) have not been studied in Chile before. This study aimed to identify Phytopythium isolates associated with root rot decline in cherry plants and to assess their pathogenicity under controlled conditions and in the field. Symptoms were recorded, and cherry plants grafted onto Maxma14 samples were collected from a commercial orchard in the Valparaíso region. We obtained isolates using selective media and characterized them based on morphological characteristics and molecular analysis of the internal transcribed spacer (ITS), cytochrome c oxidase subunit I (COX I), and β-tubulin regions. Phylogenetic analysis based on the three concatenated regions supported the placement of the three isolates within the Phytopythium. helicoides clade. Incidence across three sectors of a commercial orchard ranged from 24.3% to 42.8%. Pathogenicity tests involved inoculating one-year-old Prunus avium ‘Lapins’ plants grafted onto MaxMa14 rootstock by drenching the substrate with 300 mL of a zoospore suspension (1 × 10⁴ zoospores/mL) and evaluating them 90 days post-inoculation. Inoculated plants exhibited reduced growth, foliar symptoms, and root necrosis, compared with non-inoculated controls. These findings confirm that Phytopythium helicoides can be pathogenic in cherry trees and underscore its emerging role as a soilborne pathogen in Chilean cherry production systems.

Botryosphaeria dieback (BD) is a major trunk disease of grapevines worldwide. It is especially prevalent in Mediterranean climates. Several fungal species in the Botryosphaeriaceae family cause BD. Diplodia seriata and Neofusicoccum parvum are the most prevalent and studied. Botryosphaeria dieback has a latent endophytic phase. In this phase, fungi live inside plant tissues without causing symptoms. This is followed by a necrotrophic phase, during which fungi kill plant cells and feed on dead tissue. Stressors such as drought, high temperatures, and vine aging trigger the necrotrophic phase. Environmental stress and pathogen activity together drive disease development. Climate change likely intensifies this process. Current management is limited and relies mostly on pruning and fungicide treatment. Sustainable methods, such as clean materials, biological control, and induced resistance, are gaining relevance. This chapter reviews the taxonomy, symptomatology, epidemiology of BD, host–pathogen interactions, and environmental drivers associated with BD, with particular emphasis on Mediterranean viticulture. In addition, current and emerging sustainable management strategies are discussed as tools ti improve vineyard resilencie and lng-term productivity under changing climatic conditions.

Grapevine trunk diseases, particularly Botryosphaeria dieback, pose a major threat to vineyard sustainability, a risk that is further intensified by climate variability and increasing environmental stress. This study evaluated pathogenicity and bacterial biocontrol efficacy against Neofusicoccum parvum and Diplodia seriata under vineyard conditions, analyzing the combined effects of cultivar (Vitis vinifera L. cv. Cabernet Sauvignon and Sauvignon Blanc), tissue type (young shoots and lignified arms), and phenological season (autumn/winter and spring/summer). Pathogenicity assays revealed clear tissue-age specialization: N. parvum was more aggressive in young shoots, whereas D. seriata caused the most severe vascular lesions in lignified wood. Seasonality further modulated disease expression, with higher lesion development during spring/summer, particularly for N. parvum in young shoots, while D. seriata maintained high aggressiveness in lignified tissues across both seasons. Berry assays provided a rapid initial assessment of isolate virulence but did not fully reflect pathogen behavior in woody tissue under field conditions. Biological treatments using native bacterial strains (Pseudomonas sp. AMCR2b, GcR15a, and Rhodococcus sp. PU4) significantly reduced lesion severity in V. vinifera under field conditions, although efficacy varied by tissue type and season. Biocontrol effects were generally more stable in lignified arms, and under high disease pressure, only the most robust strains maintained consistent protection, in some cases matching or surpassing the efficacy of the fungicide tebuconazole. These results show that both pathogenicity and biocontrol performance against Botryosphaeria dieback in V. vinifera under field conditions are strongly influenced by tissue type and season, supporting bacterial biocontrol as a sustainable component of integrated disease management in vineyards.

BACKGROUND: Walnut bacterial blight, caused by Xanthomonas arboricola pv. juglandis (Xaj), leads to significant yield losses in walnut production, which is a key agricultural sector in Chile. Conventional control methods based on copper have limitations owing to environmental concerns, phytotoxicity, and bacterial resistance. Plant‐derived compounds such as polygodial offer a promising alternative as a result of their potent antibacterial properties. This study aimed to develop and evaluate the antimicrobial efficacy of nanoemulsions containing drimanic compounds, specifically polygodial ( 1 ) and epi‐polygodial ( 2 ), as a sustainable strategy to control Xaj. RESULTS: Both polygodial ( 1 ) and epi‐polygodial ( 2 ) demonstrated significant antibacterial activity against Xaj strains in vitro and in planta . In assays with immature walnut fruits, the nanoemulsion with compound 1 at 125 ppm reduced disease severity by 40%, an efficacy level intermediate between the negative control and the commercial chemical treatment (65% reduction). The nanoformulations effectively suppressed infections on leaves and shoots, and importantly, no phytotoxic effects were observed on either fruits or plants. CONCLUSION: Polygodial and epi‐polygodial are potent antibacterial agents against Xaj, making them excellent candidates for new biopesticides. This study successfully formulated these drimanic compounds into stable nanoemulsions that effectively control walnut bacterial blight without causing phytotoxicity. The development of these nanoformulations represents a significant advancement towards sustainable and effective disease management in the walnut industry, offering a viable alternative to conventional copper‐based bactericides. © 2025 Society of Chemical Industry.

Avocado, a fruit consumed worldwide and essential for countries like Mexico and Chile, faces significant postharvest challenges, particularly during prolonged storage and transportation periods, where Botryosphaeriaceae and Glomerellaceae genera cause fruit rots that can generate substantial economic losses. This study investigated three Hass avocado orchards in the Valparaíso region of Chile to identify spore dispersion peaks, analyze the aerial dynamics of fungal inoculum, and evaluate the association with climatic conditions, as well as the incidence (I) and damage index (DI) of fruit rots. Spore traps were installed in symptomatic trees and monitored weekly over 13 months. Meteorological data were collected in parallel. Fruits from these orchards were sampled to evaluate postharvest rots, physiological maturity, and disease severity using molecular techniques, including DNA sequencing and phylogenetic analysis of isolated pathogens. The results revealed that spore peaks for both fungal families were closely associated with increased rainfall and high relative humidity, particularly from June to mid-September (winter season). The Santo Domingo orchard exhibited the highest disease pressure, with stem-end rot reaching an I of 44% and a DI of 17.25%, and anthracnose reaching an I of 23% and a DI of 12.25%. This study provides the first long-term, field-based evidence of airborne spore dynamics of Botryosphaeriaceae and Glomerellaceae in Chilean avocado orchards and their statistical relationship with environmental variables. These findings highlight the potential of incorporating climatic indicators—such as rainfall thresholds and humidity levels—into monitoring and early-warning systems to optimize fungicide application timing, reduce unnecessary chemical use, and improve postharvest disease management in avocado production.

Botryosphaeria dieback, a significant grapevine trunk disease (GTD) caused by various pathogens, represents a serious threat to viticulture. Biocontrol emerges as a promising sustainable alternative to chemical control, aligning toward environmentally friendly viticultural practices. This study evaluated the in vitro, in vivo, and in situ biocontrol potential of Chilean native bacteria isolated from wild flora and endophytic communities of grapevine against Neofusicoccum parvum. In vitro biocontrol assays screened 15 bacterial strains at 10, 22, and 30 °C, identifying four Pseudomonas strains with >30% mycelial growth inhibition. In diffusible agar and double plate assays, plant growth-promoting bacteria AMCR2b and GcR15a, which were isolated from native flora, achieved significant inhibition of N. parvum growth, with reductions of up to ~50% (diffusible agar) and up to ~46% (double plate). In vivo experiments on grapevine cuttings revealed that strains AMCR2b and GcR15a inhibited mycelial growth (17–90%); younger grapevines (1–5 years) were more susceptible to N. parvum. In situ trials using Vitis vinifera L. cv. Cabernet Sauvignon and Sauvignon Blanc demonstrated higher fungal susceptibility in Sauvignon Blanc. These results highlight the potential of Pseudomonas sp. AMCR2b and GcR15a to be effective biocontrol agents against GTDs at a wide range of temperatures, contributing to sustainable viticulture.

In Chile and worldwide, walnut (Juglans regia L.) production faces significant losses due to crown and root rot caused by the phytopathogen Phytophthora cinnamomi. Currently, control methods have proven insufficient or unfavorable for the environment, increasing the need for sustainable alternatives. This research evaluates nanoemulsions based on extracts of medicinal plants endemic to Chile to control P. cinnamomi in walnut crops. The methodology included an in vitro test to determine the effective inhibitory concentrations of three nanoemulsions (N80, N90, and N100) on the mycelial growth of the phytopathogen, a test on walnut plants under controlled conditions, and two field tests using concentrations between 300 and 500 ppm. The in vitro results showed that the nanoemulsions could inhibit 90% of mycelial growth at 80 to 100 ppm concentrations. In the field, the N90 nanoemulsion at 500 ppm significantly reduced disease symptoms preventively and post-inoculation, compared with the control. This research is the first to study the use of nanoemulsions from native Chilean plants to control P. cinnamomi, showing potential to reduce the use of synthetic fungicides, contributing to safer and more ecological phytosanitary management.

The use of living organisms to treat human by-products, such as residual sludge, has gained interest in the last years. Fungi have been used for bioremediation and improving plant performance in contaminated soils. We investigated the impact of the mycorrhizal fungus (MF) Gigaspora roseae and the saprophytic fungus (SF) Coriolopsis rigida on the survival and growth of Quillaja saponaria seedlings cultivated in a sandy substrate supplemented with residual sludge. Q. saponaria is a sclerophyllous tree endemic to Chile, known for its high content of saponins. We inoculated plants with the MF, the SF, and a combination of both (MF + SF). Following inoculation, varying doses of liquid residual sludge equivalent to 0, 75, and 100% of the substrate’s field capacity were applied. After 11 months, we found a positive influence of the utilized microorganisms on the growth of Q. saponaria. Particularly, inoculation with the SF resulted in higher plant growth, mycorrhizal colonization percentage, and higher enzymatic activity, especially after the application of the sludge. This increase was more evident with higher doses of the applied sludge. These results highlight the potential of combined microorganism and residual sludge application as a sustainable strategy for enhancing plant growth and reducing waste.

Plant growth-promoting bacteria (PGPB) play a role in stimulating plant growth through mechanisms such as the synthesis of the phytohormone indole-3-acetic acid (IAA). The aims of this study were the characterization of IAA synthesis and degradation by the model aromatic-degrading bacterium Paraburkholderia xenovorans LB400, and its growth promotion of the Nicotiana tabacum plant. Strain LB400 was able to synthesize IAA (measured by HPLC) during growth in the presence of tryptophan and at least one additional carbon source; synthesis of anthranilic acid was also observed. RT-PCR analysis indicates that under these conditions, strain LB400 expressed the ipdC gene, which encodes indole-3-pyruvate decarboxylase, suggesting that IAA biosynthesis proceeds through the indole-3-pyruvate pathway. In addition, strain LB400 degraded IAA and grew on IAA as a sole carbon and energy source. Strain LB400 expressed the iacC and catA genes, which encode the α subunit of the aromatic-ring-hydroxylating dioxygenase in the IAA catabolic pathway and the catechol 1,2-dioxygenase, respectively, which may suggest a peripheral IAA pathway leading to the central catechol pathway. Notably, P. xenovorans LB400 promoted the growth of tobacco seedlings, increasing the number and the length of the roots. In conclusion, this study indicates that the versatile bacterium P. xenovorans LB400 is a PGPB.

Grapevine trunk diseases (GTDs) attack the vine’s wood, devastating vineyards worldwide. Chile is the world’s fourth-largest wine exporter, and Cabernet Sauvignon is one of the most economically important red wine varieties. Botryosphaeria dieback is an important GTD, and Diplodia seriata is one of the main pathogenic species. Biocontrol studies of these pathogens are commonly carried out at different incubation times but at a single temperature. This study aimed to evaluate the biocontrol effect of Chilean PGPB and grapevine endophytic bacteria against D. seriata at different temperatures. We analyzed the biocontrol effect of Pseudomonas sp. GcR15a, Pseudomonas sp. AMCR2b and Rhodococcus sp. PU4, with three D. seriata isolates (PUCV 2120, PUCV 2142 and PUCV 2183) at 8, 22 and 35 °C. Two dual-culture antagonism methods (agar plug diffusion and double plate) were used to evaluate the in vitro effect, and an in vivo test was performed with Cabernet Sauvignon cuttings. In vitro, the greatest inhibitions were obtained using the agar plug diffusion method and at a temperature of 8 °C, where Rhodococcus sp. PU4 obtains a 65% control (average) and Pseudomonas sp. GcR15a a 57% average. At 22 °C, only strains of Pseudomonas sp. show control. At 35 °C, one Pseudomonas strain shows the highest control (38%), on average, similar to tebuconazole (33%), and then Rhodococcus sp. (30%). In vivo, a biocontrol effect is observed against two D. seriata isolates, while the PUCV 2142 proves to be more resistant to control. The biocontrol ability at low temperatures is promising for effective control in the field, where infections occur primarily in winter.