Characterization of Alternaria porri causing onion purple blotch and its antifungal compound magnolol identified from Caryodaphnopsis baviensis

Abstract

Alternaria porri (Ellis) Clf. causes purple blotch disease on Allium plants which results in the reduction of crop yields and quality. In this study, to efficiently find natural antifungal compounds against A. porri, we optimized the culture condition for the spore production of A. porri and the disease development condition for an in vivo antifungal assay. From tested plant materials, the methanol extracts derived from ten plant species belonging to the families Cupressaceae, Fabaceae, Dipterocarpaceae, Apocynaceae, Lauraceae, and Melastomataceae were selected as potent antifungal agents against A. porri. In particular, the methanol extract of Caryodaphnopsis baviensis (Lec.) A.-Shaw completely inhibited the growth of A. porri at a concentration of 111 μg/ml. Based on chromatographic and spectroscopic analyses, a neolignan compound magnolol was identified as the antifungal compound of the C. baviensis methanol extract. Magnolol showed a significant inhibitory activity against the spore germination and mycelial growth of A. porri with IC50 values of 4.5 and 5.4 μg/ml, respectively. Furthermore, when magnolol was sprayed onto onion plants at a concentration of 500 μg/ml, it showed more than an 80% disease control efficacy for the purple blotch diseases. In terms of the antifungal mechanism of magnolol, we explored the in vitro inhibitory activity on individual oxidative phosphorylation complexes I–V, and the results showed that magnolol acts as multiple inhibitors of complexes I–V. Taken together, our results provide new insight into the potential of magnolol as an active ingredient with antifungal inhibitory action to control purple blotch on onions.

Seedborne fungi on stored onion seeds

“…Almost all samples which had Alternaria infection above 20% were grown in 2013 and 2014. The pathogenicity of A. alternata species on onion is described by Bihon et al (2015), while A. porri is a well-known pathogen of onion and could be seed-borne (Kim et al, 2022). Fortunately, A. porri was not detected on the tested seed.…”

Phytochemicals as alternative fungicides for controlling plant diseases: A comprehensive review of their efficacy, commercial representatives, advantages, challenges for adoption, and possible solutions

“… When magnolol was sprayed onto onion plants at a concentration of 500 μg/mL, it showed more than 80% disease control efficacy for the purple blotch diseases in in vivo (greenhouse) assay. [ 57 ] Trevesia palmata (aerial parts) Alternaria porri B. cinerea C. coccodes F. oxysporum P. infestans (tomato and pepper diseases) In an in vitro assay, disease control values against tomato gray mold, and tomato late blight were 82 and 88 respectively when the plants were treated with hederagenin-3- O -β- d -glucopyranosyl-(1→3)-α- l -rhamnopyranosyl-(1→2)-α- l -rhamnopyranosyl-(1→2)-α- l -arabinopyranoside ( 3 ) (500 μg/mL), a triterpene glycoside isolated from n-butanol and ethyl acetate fractions of methanol extract obtained by reflux. [ 58 ] Corydalis ternata (tubers) Botrytis cinerea (tomato gray mold) Phytophthora infestans (tomato late blight) Colletotrichum coccodes (pepper anthracnose) Isoquinoline alkaloids (dehydrocorydaline ( 8 ), stylopine ( 9 ), and corydaline ( 10 )) isolated from chloroform fraction of methanol extract exhibited in vivo antifungal activity against C. coccodes.…”

Efficiency of bio-agents and green-synthesized silver nanoparticles in controlling purple blotch disease caused by Alternaria porri in onion plants

“…It is also a highly valuable export commodity that 2 generates a sizable income. It is a widely consumed and one of the principal vegetable crops grown in a variety of locations (Schwartz and Mohan, 2007;Kim et al, 2022).…”