Olga Aguín’s scientific contributions

Gnomoniopsis smithogilvyi (Gnomoniaceae, Diaporthales) is the main causal agent of chestnut brown rot on sweet chestnut worldwide. The rotting of nuts leads to alterations in the organoleptic qualities and decreased fruit production, resulting in significant economic losses. In 2021, there was an important outbreak of chestnut rot in southern Galicia (Spanish northwest). The profile of secondary metabolites from G. smithogilvyi was studied, especially to determine its capability for producing mycotoxins, as happens with other rotting fungi, due to the possible consequences on the safety of chestnut consumption. Secondary metabolites produced by isolates of G. smithogilvyi growing in potato dextrose agar (PDA) medium were identified using liquid chromatography coupled with high-resolution mass spectrometry. Three metabolites with interesting pharmacological and phyto-toxicological properties were identified based on their exact mass and fragmentation patterns, namely adenosine, oxasetin, and phytosphingosine. The capacity of G. smithogilvyi to produce adenosine in PDA cultures was assessed, finding concentrations ranging from 176 to 834 µg/kg. Similarly, the production of mycotoxins was ruled out, indicating that the consumption of chestnuts with necrotic lesions does not pose a health risk to the consumer in terms of mycotoxins.

Gnomoniopsis smithogilvyi is an emergent pathogen that causes brown rot on nuts and burrs of sweet chestnut (Castanea sativa Mill.) in the main European producing countries, significantly reducing the production of this crop. In Galicia (northwestern Spain), this fungus was detected for the first time in 2021. In this region C. sativa is a species with high economic value, because it covers 66% of Spain’s plantations and produces 90% of the national nut production. The aim of this work was to evaluate the pathogenicity of two G. smithogilvyi strains on four cultivars of sweet chestnut from Galicia (‘Negral’, ‘Longal’, ‘Parede’ and ‘Xudía’). Nuts were surface disinfected and a superficial wound was made in the pericarp of each nut. A 5-mm mycelial agar plug of a 10-day-old culture of each G. smithogilvyi strain was inoculated. Ten nuts were treated for each strain and ten nuts inoculated with sterile PDA agar discs were used as a control. Tests were carried out twice. All of the nuts were kept in a moist chamber at 25°C. Two inoculated and two control nuts were inspected for the presence of rot symptoms every seven days. Three weeks after inoculation, the remaining nuts were examined and a disease severity index (DSI) establishing a scale of 0 to 4 was used to measure the damage. All the cultivars were affected by the pathogen with a range of disease of 0.8-2.7, while the controls remained healthy. Significant differences in severity between fungal strains of G. smithogilvyi were observed only for ‘Parede’. In all the inoculated nuts, the pathogen was re-isolated from symptomatic tissues and the identity was assessed by morphological and molecular analysis, confirming to be G. smithogilvyi.

Maize and grass silages are important dietary components for ruminant livestock that influence the quality of animal products for human consumption, such as milk, in many parts of the world. Infection of plants by fungi able to produce mycotoxins, either in the field or post-harvest, can result in a decrease of silage nutritional quality and, consequently, in milk quality. In this study, 45 maize and grass silage samples were collected from 25 dairy farms located in the north of Portugal. The occurrence of fungi was evaluated in samples, the most frequently isolated species being Aspergillus fumigatus, Dipodascus geotrichum, Mucor circinelloides, Penicillium paneum, and Aspergillus flavus. The mycotoxigenic profile of the fungal species was studied using the ultra-high-performance liquid chromatography coupled to mass spectrometry–ion trap–time-of-flight (UHPLC–MS–IT–TOF) detection. In addition, a new method based on a QuEChERS extraction followed by the UHPLC- tandem mass spectrometry (UHPLC-MS/MS) detection was developed for simultaneous analysis of 39 mycotoxins in silage. A high co-occurrence of Fusarium mycotoxins was found, although at low levels of contamination. Deoxynivalenol and beauvericin were found in more than 82% of maize silage samples. It can be highlighted the low occurrence of Penicillium and Aspergillus toxins in the maize and grass silages studied despite the frequent detection of species of both genera.

Fusarium foetens, a pathogen of Begonia plants, has been recently described as a new fungal species. This Fusarium species causes a destructive vascular wilt disease which leads to the death of the plant. Moreover, Fusarium species are known to produce a huge variety of secondary metabolites such as mycotoxins and phytotoxins. Here, we studied the toxicogenic profile of one F. foetens strain, isolated from maize, employing two methods based on the use of ultra-performance liquid chromatography coupled to mass spectrometry-ion trap-time of flight detection. The mycotoxins beauvericin and fusaric acid were detected in a pure culture of F. foetens. In addition, four fusaric acid analogs (10,11-dihidroxyfusaric acid, hydroxyfusaric acid, dehydrofusaric acid, and a hydroxylated unsaturated fusaric acid analog) were tentatively identified on the basis of their accurate mass and fragmentation patterns. Therefore, these preliminary data indicate that F. foetens isolated from maize is able to produce Fusarium mycotoxins including beauvericin and fusaric acid.

Grapevine trunk diseases (GTDs) are one of the most important groups of fungal diseases affecting grapevine plants worldwide. One of the main causes of GTDs infection occur during nursery plant production processes. The phytosanitary status was determined for 150 young grapevine plants (two varieties grafted onto different rootstocks) that were produced in three European nurseries. Some plants were analyzed upon submission, while others were assessed after up to 12 months growth in agreenhouse. Fungal species associated with GTDs were identified and characterized from the scions, graft unions, rootstocks, or roots. A total of 449 fungal isolates associated with GTDs were obtained, and 20 species were identified by morphological characteristics and DNA analyses. Five species were involved in Botryosphaeria dieback, six in black foot disease, six in Diaporthe dieback,and three in Petri disease. Incidence of GTDs on grapevine plants was between 81 and 100%, with different diseases varying between rootstocks and grapevine varieties. Isolates of other fungal genera not involved in the GTD complex were also detected, including Colletotrichum, Fusarium, and Rhizoctonia.The high presence of GTDs during nursery production of grapevine plants raises the need to implement effective control methods that could prevent the spread of these diseases to vineyards.

Bunch rot of Vitis vinifera is frequently caused by a complex of filamentous fungi. In a study on non-Botrytis fungi associated with bunch rot at harvest in northwestern Spain, rotting berries showing pink masses were observed in bunches of V. vinifera Albariño in one vineyard that experienced prolonged warm, moist conditions before harvest. The aim of this work was to identify the fungal species and determine its pathogenicity on grapes. Fungal isolates not corresponding morphologically to any known genus associated with bunch rot were obtained from the pink masses. Morphological and molecular phylogenetic analyses revealed that the isolates belonged to Pilidium lythri, an opportunistic pathogen causing tan-brown rot on strawberry. Most frequent non-Botrytis grape-rotting fungi at the vineyard were Penicillium brevicompactum, Penicillium expansum, and Talaromyces purpurogenus, while P. lythri had a low isolation frequency. Pathogenicity tests showed that P. lythri caused tan-brown rot in berries of the V. vinifera table grape varieties Regal Seedless and Red Globe. That P. lythri can directly infect healthy grape berries suggests that it may be a true pathogen associated with bunch rot on grapevine. Its presence on berries may contribute to postharvest decay of table and wine grapes. © 2018 by the American Society for Enology and Viticulture. All rights reserved.

The disease huanglongbing (HLB), caused by the phloem-limited and psyllid-vectored 'Candidatus Li-beribacter' spp., is threatening the Mediterranean citrus industry. The African psyllid (Trioza erytreae) vector of the pathogen was detected in Madeira (Portugal) in 1994 and in the Canary Islands (Spain) in 2002, and its arrival in 2014 in northwest Spain and Portugal along the Atlantic coast instigated a biological alert, and a contingency management plan was developed. Extensive surveys were conducted in Canary Islands from 2009 to 2015 and in the northwest mainland Spain (Galicia) since the first detection of T. erytreae. Symptoms of the psyllid were observed in most sweet orange orchards of five islands in Canary Islands (93% of the inspected plots). In northwest mainland Spain, 65% of the inspected plots up to 2016 showed T. erytreae symptoms. During the surveys, ten leaves/tree from trees showing suspicious symptoms and from symptomless trees, as well as adult psyllids, were collected and analysed by real-time PCR using a universal 'Ca. Liberibacter' spp. kit, according to the EPPO standard. Suspected samples from other surveyed Spanish regions free of the vector were also analysed. The few samples that were positive in the screening test were tested by species-specific real-time PCR protocols, and they did not show amplification. These data confirm that the Spanish citrus industry is currently free of the 'Ca. Liberibacter' spp., but strict measures to prevent the introduction of this pathogen are required as the presence of T. erytreae increases the risk of its dissemination.