Since 2007, Chilean avocado (Persea americana Mill.) orchards have been exposed to several abiotic stress conditions, namely frost damage and drought, due to three consecutive seasons of cold winters and shortage of irrigation water. At the same time, a severe disease resulting in tree dieback of cv. Hass, specifically, was observed in north-central Chile. Symptomatic trees exhibited abundant dead twigs in the tree canopy, and wilted leaves remained attached to the twigs in autumn. Closer inspection revealed reddish-brown necrotic lesions on the bark of the dead twigs, which girdled these symptomatic branches. When the bark was removed, the wood below appeared dark brown, in contrast to the yellowish-green coloring of healthy. The fungus was also consistently isolated from rotted fruit. A Neofusicoccum sp. with a yellow colony was consistently isolated from the necrotic lesions on PDA and incubated at room temperature for 3 days. Conidia produced in black pycnidia growing on 2% water agar with sterilized pine needles were smooth, unicellular, hyaline, and with granular contents. One or two septa developed at germination, but rarely before. The average length of the conidia was 27.0 ± 0.9 μm, with a length/width ratio of 3.9 ± 0.2 μm. Based on culture and conidial morphology, the isolates were putatively identified as Neofusicoccum luteum (1). DNA sequence analysis of the rDNA internal transcribed spacer (ITS) region was conducted for four representative isolates using primers ITS1 and ITS4 (4). The sequence analysis of ITS region of kiwifruit isolate H1M4 (Accession No. KC330230) reveled 100% nucleotide identity to N. australe (FJ157187 to FJ157192) (3). Pathogenicity tests were conducted with stem inoculations of 2-year-old cv. Hass plants grow in plastic containers in a sand/lime/peat mixture. For each inoculated plant (n = 8), a 7-mm-diameter agar plug from the margin of a 3-day culture was used as inoculum after wounding the stem to the depth to 7 mm with a cork borer. Negative control (n = 8) were wounded and then ‘mock-inoculated’ with sterile agar plugs. The inoculation sites were wrapped with Parafilm. All plants were kept in a greenhouse. After 5 months, all inoculated plants showed bark cankers and necrotic lesions beneath the bark, which were 5.2 cm long (n = 8). No symptoms developed on the control plants. N. australe was recovered from the margin of the necrosis lesion of every inoculated plant, thus fulfilling Koch's postulates and confirming its pathogenicity. Botryosphaeraceae spp. are the commonly reported to have ability to survive endophytically in their host, causing disease only when the host is exposed to a stress condition (2). To our knowledge, this is the first report of N. australe as a pathogen of avocado in Chile. The fungal isolates (PaHass No. 1 to 4) were deposited in the Laboratorio de Fitopatología Frutal y Molecular, Departamento de Sanidad Vegetal, Facultad de Ciencias Agronómicas de la Universidad de Chile. References: (1) A. J. L. Phillips. http://www.crem.fct.unl.pt/botryosphaeria_site/ Accessed November 20, 2011. (2) B. Slippers and M. J. Wingfield. Fungal Biol. Rev. 21:90, 2007. (3) B. Slippers et al. Mycologia 96:1030, 2004. (4) White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

Table grapes are highly susceptible to Botrytis cinerea infections during the bloom period. After reaching the flower development stage, B. cinerea remains quiescent until berry ripening or gives rise to blossom blight under specific climate conditions. A research study was conducted on the Chilean Central Valley during the 2018–2019 growing season. Flowers of Vitis vinifera cv. Thompson Seedless were collected and B. cinerea was isolated together to a second and morphologically different species, characterized by white mycelium and low to no sporulation (11.4% of total isolates). Three randomly selected isolates within this population were genetically examined and identified as Botrytis prunorum based on a phylogenetic multilocus approach using partial regions of genes RPB2, HSP60, and G3PDH or NEP1 and NEP2. Pathogenicity tests showed that B. prunorum infects and causes wilting in healthy table grape flowers. B. prunorum isolates were able to infect Thompson Seedless berries, inducing lesions between 13.11 and 41.53% with respect to the lesion diameter generated by B. cinerea B05.10. The fungicide sensitivity was evaluated. The three genetically characterized isolates were sensitive to boscalid and to cyprodinil/fludioxonil mixture with a mean EC₅₀ value of 5.5 µg/ml and 0.065 µg/ml, respectively. However, loss of sensitivity to fenhexamid was determined, with a mean EC₅₀ value of 5.13 µg/ml. Our understanding about blossom blight in V. vinifera has been limited to B. cinerea. Here we associated B. prunorum as a second causal agent of this disease in Chile. This data represents a first approach to the epidemiological characteristics of B. prunorum associated with blossom blight in table grapes.

Fludioxonil is a highly effective phenylpyrrole fungicide for controlling Botrytis cinerea. Although the field efficacy of fludioxonil remains high, Botrytis cinerea isolates with reduced sensitivity have been reported globally. The molecular target of fludioxonil still remains unknown; however, a mechanism of reduced sensitivity to fludioxonil underlies the overexpression of the ATP binding cassette (ABC) transporter AtrB in a dependent pathway of the Mrr1 transcription factor. Fludioxonil is a key player in controlling B. cinerea infection in table grapes in Chile. However, some isolates with a reduced sensitivity to fludioxonil were detected. This study observed endogenous atrB overexpression in Chilean isolates with reduced sensitivity to fludioxonil (n = 22) compared to the sensitive isolates (n = 10). All isolates increased the expression of atrB in a growth medium supplemented with fludioxonil (0.05 μg/mL). However, sensitive isolates showed lower atrB expression than those with reduced fludioxonil sensitivity. Remarkably, a mutant version of the transcription factor Mrr1 carrying 21 amino acid modifications was identified in all isolates with reduced sensitivity to fludioxonil. These changes alter the protein’s transcription factor domain and the C-terminal portion of the protein but not the Zn (2)-C6 fungal-type DNA-binding domain. These results suggest a direct relationship between the conserved and divergent mutant version of mrr1 and sensitivity to fludioxonil. This study provides a new target for developing molecular diagnostic strategies to monitor B. cinerea’s sensitivity to fludioxonil in the field.

In Chile, the 2019-2020 sweet cherry season yielded 228,548 t, produced on 38,392 hectares and an average annual crop value about US$1.6 billion (http://www.iqonsulting.com/yb/). Between autumn 201...

The main phytosanitary problem for table grape production in Chile is gray mold caused by the fungus Botrytis cinerea. To manage this issue, the primary method utilized is chemical control. Fludioxonil, a phenylpyrrole, is highly effective in controlling B. cinerea and other plant pathogens. Consistently, there have been no field reports of reduced efficacy of fludioxonil; however, subpopulations with reduced sensitivity to fludioxonil are on the rise globally, as per increasing reports. Our study involved a large-scale evaluation of B. cinerea’s sensitivity to fludioxonil in the Central Valley of Chile’s primary table grape production area during the growing seasons from 2015 to 2018. Out of 2,207 isolates, only 1.04% of the isolates (n = 23) exceeded the sensitivity threshold value of 1 μg/ml. Remarkably, 95.7% are concentrated in a geographic region (Valparaíso Region). Isolates with reduced sensitivity to fludioxonil showed growth comparable with sensitive isolates and even more robust growth under nutritional deficit, temperature, or osmotic stress, suggesting greater environmental adaptation. When table grape detached berries were stored at 0°C, isolates less sensitive to fludioxonil caused larger lesions than sensitive isolates (2.82 mm compared with 1.48 mm). However, the lesions generated by both types of isolates were equivalent at room temperature. This study found no cross-resistance between fludioxonil and fenhexamid, an essential fungicide integrated with fludioxonil in Chilean B. cinerea control programs. All the Chilean isolates with reduced sensitivity to fludioxonil were controlled by the fludioxonil/cyprodinil mixture, a commonly employed form of fludioxonil. The cyprodinil sensitivity in the isolates with reduced sensitivity to fludioxonil explains their low field frequency despite their null fitness penalties. However, the emergence of fludioxonil-resistant isolates inside the Chilean B. cinerea population demands a comprehensive analysis of their genetic bases, accompanied by monitoring tools that allow the permanence of field fludioxonil efficacy.

Cuttings of fi ve grapevine (Vitis vinifera) rootstocks were wounded and immediately inoculated with suspensions (approximately 5x103 conidia·mL-1) of either Phaeomoniella chlamydospora, Phaeoacremonium aleophilum or a mixture of both species. The presence of these endophyte fungi affected the quality of each of the fi ve rootstocks. Among the roostocks investigated in this study, 1103P and 101-14 MG were less susceptible to the infection caused by Pa. chlamydospora and Pm. aleophillum.