A fungal glycoprotein mitigates passion fruit woodiness disease caused by Cowpea aphid-borne mosaic virus (CABMV) in Passiflora edulis

Passion fruit woodiness disease is responsible for severe losses in passion fruit production around the world. The disease is caused by Cowpea aphid-borne mosaic virus (CABMV), an aphid-transmitted potyvirus. Traditional sanitary measures against the disease, such as vector elimination and cross protection, have not been successful, resulting in elimination and replanting of passion fruit plants each season. To find new alternatives for disease control, we tested the use of a peptidogalactomannan (pGM) extracted from the fungus Cladosporium herbarum to activate passion fruit defense mechanisms, enabling plants to tolerate passion fruit woodiness disease (PWD). Passion fruit seedlings were spray-treated with pGM in a greenhouse three days before mechanical inoculation with CABMV. Experiments were set up in a completely randomized design, and disease incidence and severity were compared between water- and 100 μg ml−1 pGM-treated plants. Woodiness symptoms and certain developmental parameters of water- and pGM-treated plants were evaluated over five weeks. pGM treatment did not affect plant normal development. Plants that were both treated with pGM and inoculated with the virus showed very mild or no foliar CABMV disease symptoms and had the same growth and developmental patterns as the healthy uninoculated control plants. pGM led to the accumulation of antioxidant enzymes such as peroxidase and superoxide dismutase in the leaf tissues as well as their respective mRNAs. In addition, a ten- and twofold transcription induction of the mRNAs of the defense-related genes such as chitinase I (PR-3) and phenylalanine ammonia-lyase (PAL), respectively, were observed in pGM-treated seedlings. These results suggested that pGM enables plants to respond more intensely to CABMV infection, mitigating woodiness symptoms and maintaining normal plant growth.