Paecilomyces formosus: a new pathogen of trees
Several reports of a new disease of trees caused by Paecilomyces formosus (syn. P. maximus) have recently been made from several countries around the Mediterranean Basin. The fungus was previously known for its pathogenicity to animals, and humans (causing cutaneous and lung infections). Until recently, on plants P. formosus was mainly recorded in association with decaying plant debris and wood. For example, it has been detected in wood samples of Hevea brasiliensis in Indonesia, in association with other fungi causing wood stain. It has also been found in wooden electricity utility poles in South Africa.
In Iran, P. formosus was first reported causing bark cankers on twigs and branches, as well as dieback on pistachio (Pistacia spp.) trees in 2015. It is suspected that the fungus has been causing damage on pistachios much earlier, but was reported at that time as P. variotii. Since 2015, P. formosus has been reported in many Iranian provinces as the cause of dieback on the following woody plants: Acer monspessulanum, Anagyris foetida, ,Azadirachta indica Caesalpinia gilliesii, Crataegus pontica, Ficus carica, Haloxylon sp., Malus domestica, Nerium oleander, Paliurus spina‐christi, Pistacia atlantica, Pistacia mutica, Prunus avium, Prunus dulcis, Prunus lycioides, Prunus microcarpa, Prunus scoparia, Punica granatum, Quercus brantii, Quercus libani, Salix acmophylla, Tamarix aphylla, Tamarix hispida, Tamarix ramosissima, Ziziphus spina-christi. In particular, recent studies have shown that P. formosus played a major role in the dieback of oak trees (Quercus brantii) in the Zagros forests (Western Iran) and that it could be detected in various wood boring insects, such as Acmaeodera sp., Chrysobothris affinis, Monochamus sp., Trichoferus campestris. However, more studies are needed to determine whether any of these insects could be vectors of P. formosus.
In Türkiye, P. formosus was first reported in summer 2022 causing disease symptoms on fruit trees. It was observed in apricot (Prunus armeniaca cv. Hacıhaliloğlu) trees in a commercial orchard (2 ha) in Elazığ province. Diseased trees (approximately 3%) showed branch cankers, wilting, gummosis, internal wood discoloration and dieback. Dieback and cankers were also observed on cherry (P. avium) trees in an orchard in Çınar, district of Diyarbakır. The disease incidence was approximately 5%. Symptoms included blight and branch canker, darkened bark, wood discoloration, and dieback.
In Morocco, P. formosus has been isolated from cedar (Cedrus atlantica) trees in the Tazekka National Park, near the city of Taza. The fungus was isolated from decaying wood.
Sources
Chauiyakh O, El Fahime E, Ninich O, Aarabi S, Bouziani M, Chaouch A, Tahir AE (2023) First report of the lignivorous fungus Paecilomyces maximus in Cedrus atlantica M. in Morocco. Wood Research 68(2), 403-412.
Ghaderi G, Jamali S, Haack RA, Valipour J (2024) Detection of Paecilomyces formosus in wood‑boring beetles associated with oak dieback and decline in the Zagros forests of Iran. Journal of Pest Science. https://doi.org/10.1007/s10340-024-01805-x
Heidarian R, Fotouhifar KB, Debets AJ, Aanen DK (2018) Phylogeny of Paecilomyces, the causal agent of pistachio and some other trees dieback disease in Iran. PLoS One 13(7), e0200794. https://doi.org/10.1371/journal.pone.0200794
Nandika D, Arinana A, Salman AB, Putri JY (2021) Morphological and molecular features of stain fungi infecting rubberwood (Hevea brasiliensis). Biodiversitas Journal of Biological Diversity 22(12), 5408-5416.
Ören E, Karakuş Y, Şimşek M, Ozan GN, Bayraktar H (2023) First report of Paecilomyces maximus causing dieback and canker on apricot in Turkey. Journal of Plant Pathology 105, 1175–1176.
Ozan GN, Çaplık D, Bayraktar H (2024) First report of Paecilomyces maximus causing dieback on cherry in Türkiye. Journal of Plant Pathology 106, 1875–1876. https://doi.org/10.1007/s42161-024-01717-w
Rostami T, Jamali S (2022) First report of dieback of Salix acmophylla caused by Paecilomyces formosus in Iran. Plant Disease 106(9), 2518. https://doi.org/10.1094/PDIS-12-21-2812-PDN
Sabernasab M, Jamali S, Marefat A, Abbasi S (2019) Molecular and pathogenic characteristics of Paecilomyces formosus, a new causal agent of oak tree dieback in Iran. Forest Science 65(6), 743–750. https://doi.org/10.1093/forsci/fxz045
Urquhart AS, Idnurm A (2023) A polyphasic approach including whole genome sequencing reveals Paecilomyces paravariotii sp. nov. as a cryptic sister species to P. variotii. Journal of Fungi 9(3), 285. https://doi.org/10.3390/jof9030285