Xanthomonas arboricola pv. juglandis (hereafter X. juglandis) is the etiological agent of walnut blight, the most important bacterial disease affecting walnut production worldwide. Currently, the disease is treated mainly with copper-derived compounds (e.g., CuSO₄) despite the evidence of genetic resistance in these strains. Regarding the effectiveness and sustainability, the use of a bacteriophage appears to be a biocontrol alternative to reduce X. juglandis load and symptomatology of walnut blight. Here, the phages f20-Xaj, f29-Xaj, and f30-Xaj were characterized, and their effectiveness in walnut orchards against walnut blight was determined. These bacteriophages showed a specific lytic infection in X. juglandis strains isolated from Chile and France. Phylogenetic analysis of the complete genome of f20-Xaj and f30-Xaj indicates that these phages belong to the Pradovirus genus. In the field, the cocktail of these bacteriophages showed similar effectivity to CuSO₄ in the reduction of incidence and severity in walnut tissue. Moreover, the bacterial load of X. juglandis was significantly reduced in the presence of bacteriophages in contrast to a CuSO₄ treatment. These results show that the use of bacteriophages can be an alternative to combat the symptoms of walnut blight caused by X. juglandis.

Kiwifruit (Actinidia spp.) is an important crop in Chile, ranking as the sixth largest producer globally with 7566.5 hectares currently planted (ODEPA, 2024). Additionally, it is the second major exporter in the Southern Hemisphere, following New Zealand. In July 2023, Actinidia deliciosa cv. Hayward from Curicó in the O'Higgins Region (34°58'58.0"S 71°14'22.0"W) exhibited sour rot symptoms upon arrival at the destination market in the Northern Hemisphere, with a 30% incidence per box and up to 50% tissue damage. Thereafter, another set of ten fruits was collected from the orchard and incubated at room temperature (>80% relative humidity) for 30 days. These fruits developed soft rot at the stem end, sunken lesions, a sour odor, and white mycelial growth. Fungal isolations were performed by surface-disinfecting the kiwifruits with 70% ethanol. Small pieces of internal tissue (5x5 mm) were taken from the lesion margin of damaged fruits and transferred to PDA plates with streptomycin and penicillin (100 mg/L). After 3 days of incubation at 24°C, all isolates exhibited white, flat, milky yeast-like colonies with radial mycelial growth. Three single-spore isolates were obtained from the plates. Microscopic examination revealed septate, branched hyphae, with single-celled cylindrical arthroconidia-like structures measuring 2.13 to 9.43 × 2.01 to 3.92 μm (n=100), consistent with Geotrichum sp. (De Hoog et al. 1986). Molecular identification of the one single isolate designated CH95 was achieved through PCR amplification and sequencing using the ITS1/ITS4 primers (White et al. 1990) and the large subunit ribosomal RNA (LSU rRNA) using the D1/D2 primers (Kurtzman and Robnett 1998) (GenBank: PP387457.1, PQ628079.1), confirming G. candidum through BLAST and phylogenetic analysis. BLAST searches indicated the highest nucleotide sequences with the neotype strain of G. candidum CBS 615.84 (ITS: 99.76%, OP765493.1; LSU rRNA: 98.62%, OP763665.1). The identity of the isolated CH95 was confirmed with multilocus phylogenetic analysis using the IQ-TREE server (Trifinopoulos et al., 2016) Pathogenicity tests were performed on the surface disinfected (70% ethanol) Hayward kiwifruits, which were wounded (0.8 mm in diameter and 5 mm in depth) and inoculated with G. candidum (20 µL of 107 conidia/mL). Control fruits were treated with sterile water. After 20 days at 24°C inoculated fruits showed rot and white mycelium, while controls remained healthy. The pathogen was re-isolated, fulfilling Koch's postulates. The results confirmed identical morphological characteristics to the initial isolate, and sequencing results verified the identity of the isolate as G. candidum. G. candidum is widely distributed worldwide and has been reported to cause sour rot in tomatoes (Bourret et al. 2013), strawberries (Ma et al. 2018), stone fruits (Yaghmour et al. 2012) and more recently, in kiwifruit (Cheng, et al. 2021). In Chile, studies on this pathogen have been limited, and the incidence or losses on kiwifruit postharvest remain unknown. This is the first report of G. candidum in Hayward kiwifruit in Chile, highlighting the need for further studies on epidemiology and specific control strategies.

Sweet cherry (Prunus avium L.) is the primary tree fruit cultivated in Chile, with 70,686.29 ha currently planted, and it is the main exporter of sweet cherries in the Southern Hemisphere (www.ciren.cl, 2024). During the 2022 spring season (october), cherry trees in a commercial orchard in Calera de Tango, Metropolitan Region (33°39'42.8"S 70°45'50.6"W) showed decline symptoms, affecting 35% to over 50% of the trees. Symptoms included poor growth, chlorotic leaves, wood cankers, dead twigs, and dieback of branches, early defoliation and in several cases tree dead. Cross-sections of symptomatic branches revealed dark brown necrosis. Small pieces of symptomatic stems/branches (n=5) were surface disinfected with 70% ethanol and rinsed in sterile distilled water. Sections of inner bark and xylem tissue were cut from the margin of the necrotic lesion and transferred onto Petri dishes containing potato dextrose agar (PDA) supplemented with streptomycin and penicillin (100 mg/L). After 4 days of incubation at 25°C, five white and cottony colonies were observed. It was also evident how the aerial mycelium changed color with age to dark gray. Under the microscope, septate, branched hyphae were observed, which were either hyaline or melanized. Pycnidia and conidia were induced by incubating twigs in a humid chamber (>80% RH) at 20°C in the dark for 10 days. Black, globose pycnidia developed on bark surfaces. Conidia were hyaline, unicellular, and ellipsoidal to fusiform, with truncated ends, measuring 25.07 - 38.16 (29.07) μm x 7.23-11.62 (9.46) μm (n=50), and a length/width ratio of 3.07. Based on morphology, isolates were preliminarily identified as Neofusicoccum sp. A single-hyphal-tip culture (HK01) was used for molecular identification. The rDNA internal transcribed spacer (ITS), RNA polymerase II second largest subunit (Rpb2), and translation elongation factor 1-alpha (Ef1-α) partial gene regions were amplified by polymerase chain reaction (PCR) and sequenced using the primers ITS5/ITS4 (White et al. 1990), RPB2bot6F/RPB2bot7R (Sakalidis et al. 2011), and EF1-728F/EF1-986R (Carbone and Kohn 1999), respectively. BLAST searches indicated the highest nucleotide sequences with the reference strains of Neofusicoccum parvum CMW 9081 (ITS: 99.76%, AY236943; Rpb2: 100%, EU821963 y Ef1-α: 94.65%, AY236917). The identity of isolated HK01 was confirmed with multilocus phylogenetic analysis. Pathogenicity tests were conducted on 2-year-old 'Lapins', 'Kordia' and 'Santina' sweet cherry trees (n=3). Mycelial plugs (5 mm) from active culture were inoculated into wounds on the main stem and sealed with Parafilm; controls received PDA plugs only. The experiment was performed twice. After 6 months, the inoculated trees developed characteristic necrotic vascular lesions (length: 35-80 mm; width: 22-45 mm), and gummosis. However, control trees remained asymptomatic. The fungus was reisolated only from inoculated branches and molecularly identified (EF1), fulfilling Koch's postulates. Neofusicoccum spp. play an important role in dieback and stem canker in Chile (Lolas et al., 2024; Barcos et al., 2023) and have been associated with significant economic losses in woody plants worldwide (Belair et al., 2021). This, along with the considerable expansion of sweet cherry production in Chile, emphasizes the necessity for appropriate and specific control strategies to manage the disease.