First Report of Fusarium avenaceum Causing Postharvest Decay of European Pear in Mid-Atlantic United States.

Fruit losses due to postharvest decay caused by several fungal species is a major challenge for pear production (Sardella et al. 2016). In December 2021, a European pear (Pyrus communis L.) 'Dawn' with brown, circular, watery, and sunken lesions was observed in cold storage at the USDA Appalachian Fruit Research Station in Kearneysville, West Virginia. Only 1 of 14 'Dawn' pears examined in cold storage had the described disease symptoms. The fruit was surface sterilized, and symptomatic tissue was transferred to potato dextrose agar (PDA) and incubated at 25°C under continuous light. The isolate was hyphal tip purified and propagated on PDA plates at 25°C. The colonies grew an average of 8 mm/day and produced fluffy white aerial mycelium and pigmented rings of golden yellow which then darkened to pink with a dark pink on the reverse. The isolate was also cultured in liquid basal medium with carboxymethyl cellulose (Moura et al. 2020) for 7 days at 25°C to promote macroconidia formation. Macroconidia were slightly falcate with a tapering apical cell, usually 2 to 4 septate, and on average 16.8 µm long by 2.8 µm wide. The isolate was identified as Fusarium spp. based on morphology. Identity of the isolate was confirmed through sequencing of the ITS and TEF1 gene region (Stielow et al. 2015). The ITS and TEF1 sequences were deposited in GenBank (OP007197 and OP007198). BLAST analysis of the ITS amplicon identified multiple Fusarium spp. with 100% identity and 100% query coverage including F. avenaceum KJ562378. BLAST analysis of the TEF1 amplicon showed 99% identity and 99-100% query coverage with F. avenaceum isolates KM189442 and MK512754. Organic Bartlett pears were surface sanitized with a 1% aqueous chlorine solution, rinsed with sterile water and dried in a laminar flow hood. Fruit were then wounded with a sterile nail (4 mm diameter x 4 mm depth) and inoculated with a 4 mm mycelial plug taken from a 7- to 10-day old culture on PDA and wrapped with Parafilm. Plugs taken from sterile PDA were used as a control. Inoculated fruit were stored at 25°C in fruit trays in plastic bins for 7 days. Six fruit composed a replicate, and the experiment was repeated for a total of two replications. Lesions developed within 48 hours and expanded to an average of 28.5 mm by day 7. No lesions were observed on control fruit. Symptoms observed on inoculated pears were the same as the decay observed on the original pear obtained from cold storage. Fungal colonies isolated from the lesions and cultured on PDA morphologically resembled the original isolate from the infected pear. In 2014, F. avenaceum was first reported in the United States to cause post-harvest decay of apples in Pennsylvania (Kou et al. 2014). In the Netherlands, F. avenaceum has been reported to cause postharvest decay of 'Conference' pears but was observed at low frequencies (1-5%) in packing-house surveys (Wenneker et al. 2016). Fusarium spp. was also recently found on European pears in Southern Oregon (KC and Rasmussen 2020). F. avenaceum can produce mycotoxins which is a concern for fruit processing (Munkvold et al. 2021). Monitoring for this pathogen to prevent losses and mycotoxin contamination of processed fruit products will be import for consumer safety. To our knowledge, this is the first report of F. avenaceum causing postharvest decay of European pear in the Mid-Atlantic region of the United States.

Exposure in vitro to an Environmentally Isolated Strain TC09 of Cladosporium sphaerospermum Triggers Plant Growth Promotion, Early Flowering, and Fruit Yield Increase.

A growing number of bacteria and fungi have been found to promote plant growth through mutualistic interactions involving elements such as volatile organic compounds (VOCs). Here, we report the identification of an environmentally isolated strain of Cladosporium sphaerospermum (herein named TC09), that substantially enhances plant growth after exposure in vitro beyond what has previously been reported. When cultured on Murashige and Skoog (MS) medium under in vitro conditions, tobacco seedlings (Nicotiana tabacum) exposed to TC09 cultures for 20 days increased stem height and whole plant biomass up to 25- and 15-fold, respectively, over controls without exposure. TC09-mediated growth promotion required >5 g/L sucrose in the plant culture medium and was influenced by the duration of exposure ranging from one to 10 days, beyond which no differences were detected. When transplanted to soil under greenhouse conditions, TC09-exposed tobacco plants retained higher rates of growth. Comparative transcriptome analyses using tobacco seedlings exposed to TC09 for 10 days uncovered differentially expressed genes (DEGs) associated with diverse biological processes including cell expansion and cell cycle, photosynthesis, phytohormone homeostasis and defense responses. To test the potential efficacy of TC09-mediated growth promotion on agricultural productivity, pepper plants (Capsicum annuum L.) of two different varieties, Cayenne and Minisweet, were pre-exposed to TC09 and planted in the greenhouse to monitor growth, flowering, and fruit production. Results showed that treated pepper plants flowered 20 days earlier and yielded up to 213% more fruit than untreated controls. Altogether the data suggest that exposure of young plants to C. sphaerospermum produced VOCs may provide a useful tool to improve crop productivity.