First Report of Pestalotiopsis trachicarpicola Causing Apothecium Wither on Cultivated Morchella sextelata in Sichuan, China

Morel (Morchella sextelata) is a valuable medicinal and edible mushroom, but the wild yield is seriously insufficient, so several artificial varieties have been developed to alleviate the shortage of wild yield. However, in 2020-2022, apothecium wither symptoms were observed in Nanchong, Sichuan. A total of 30.80% of the morels in the planting base (1.3 km2) showed these symptoms. The initial symptoms were slight white lesions on the surface of apothecium, then the mycelia gradually invaded the interior of the fruiting body, and eventually leading to black and wilt apothecium (Fig. 1a). Fifteen symptomatic morels were collected and ten isolates were obtained using the single spore isolation technique developed by Chomnunti et al. (2014). The morphological characteristics of the ten isolates were similar, which showed dense aerial white mycelia colony texture on PDA, and later forming concentric black mucus (Fig. 1c). The reverse side was yellow (Fig. 1d). The acervulus was floral-shaped and discrete, with smooth walls and measured 120.0 to 400.5 × 15.5 to 40.0 μm (n=10) (Fig. 1e); the conidia were fusiform and hyaline, 21.0 to 28.6 × 6.0 to 7.6 μm in size (n=50), each contained five cells. The apical cell was hyaline, conic and with 2 to 4 tubular apical appendages on the top. The three intermediate cells were brown to olivaceous, doliform to cylindrical, constricted at septa. The basal cell was conic to acute (Fig. 1f). The morphological characteristics were consistent with the published description of Pestalotiopsis trachicarpicola (Maharachchikumbura et al., 2012). PCR was performed with primers ITS1/ITS4 for internal transcribed spacer (ITS) (White et al., 1990), BT2A/BT2B for β-tubulin gene (TUB) (Glass and Donaldson, 1995), and EF1-526F/EF1-1567R for translation elongation factor 1-alpha (TEF-1α) (Roger et al., 1999). The pairwise alignments of ITS, TUB, and TEF-1α sequences was nearly 100% identical to P. trachicarpicola with GenBank accession numbers MT889666.1 (579/585 bp, 99%), MT884145.1 (445/450 bp, 99%), and MW149930.1 (946/958 bp, 99%), respectively. The resulting sequences were deposited in GenBank (Accession no. ITS: OL362082; TUB: OL828342; and TEF-1α: OL905009). Phylogenetic analysis performed with maximum likelihood method used MEGA 7.0 (1000 bootstrap replications) classified WLM5 into the P. trachicarpicola clade (Fig. 2), so we finally confirmed the identity of WLM5 as P. trachicarpicola. To fulfill Koch's postulates, twenty morels were surface disinfected with 2% sodium hypochlorite and then artificially wounded (diameter of 0.5 mm) prior to inoculation with 200 μL conidial suspension (105 conidia/mL), while an equal amount of sterile distilled water was applied to controls. After 4 days, the inoculated fruiting bodies showed symptoms consistent with field infection (Fig. 1b) and P. trachicarpicola was re-isolated using the same protocol, while the control remained asymptomatic. This first report of P. trachicarpicola causing apothecium wither on morel will help develop robust disease management strategies against this emerging fungal pathogen.

Pestalotiopsis trachicarpicola, a novel pathogen causes twig blight of Pinus bungeana (Pinaceae: Pinoideae) in China

Pinus bungeana is one of indigenous trees in China and widely distributed in poor and arid regions for vegetation and industrial woody use. However, since a high-incidence disease threatens the growth of mature P. bungeana tree in the garden and in the plantation every year, the overwintering shoots were infected and died in the next spring with a ratio over 70%, but the cause was beyond understood. A total of 120 fungal isolates were separated from symptomatic twigs by histological isolation methods, including Pestalotiopsis spp., Fusarium spp., Trichothecium spp., Penicillium and some unknown fungal species. Pestalotiopsis spp. was dominant, accounting for 85%. Morphological observation under microcopy showed all Pestalotiopsis species are identical, and six isolations among them were randomly selected for pathogenicity tests. Fulfilling Koch's postulates showed that all six isolates of Pestalotiopsis spp. were pathogens of twig blight, causing the same symptoms as observed in the field, while other non-Pestalotiopsis isolates were avirulent to P. bungeana twigs. Multi-gene (ITS, tub2 and TEF1) analysis and morphological observation revealed that all the six Pestalotiopsis isolates belonged to P. trachicarpicola. To our knowledge, this is the first study reporting P. trachicarpicola as the pathogens responsible for P. bungeana twig blight in China.