Abstract
Alternaria dauci is the causal agent of Alternaria leaf blight (ALB) in carrot (Daucus carota) crops around the world. However, to date, A. dauci has received limited attention in its production of phytotoxic metabolites. In this investigation, the bioassay-guided isolation of the extract from liquid cultures of A. dauci resulted in the isolation of two metabolites identified as α-acetylorcinol (1) and p-hydroxybenzoic acid (2), based on their spectroscopic data and results from chemical correlation reactions. Testing of both metabolites in different assays showed an important phytotoxic activity for p-hydroxybenzoic acid (2) when tested in the leaf-spot assay on parsley (Petroselinum crispum), in the leaf infiltration assay on tobacco (Nicotiana alata) and marigold (Tagetes erecta), and in the immersion assay on parsley and parsnip (Pastinaca sativa) leaves. Quantification of the two metabolites in the crude extract of A. dauci kept at different times showed that p-hydroxybenzoic acid (2) is one of the first metabolites to be synthesized by the pathogen, suggesting that this salicylic acid derivative could play an important role in the pathogenicity of the fungus.
Highlights
The Alternaria genus is well-known for its pathogenicity against many economically important crops worldwide [1,2]
A. dauci, leaf-spot assay on parsley leaves as a guide, resulted in the fraction theof extract of A.using dauci,the using the leaf-spot assay on parsley leaves as a guide, resulted isolation of two phytotoxic metabolites identified as α-acetylorcinol and p-hydroxybenzoic acid in the isolation of two phytotoxic metabolites identified as α-acetylorcinol (1) and p-hydroxybenzoic
These results indicate that p-hydroxybenzoic acid (2) is one of the first metabolites produced by A. dauci in the liquid culture conditions used in this investigation
Summary
The Alternaria genus is well-known for its pathogenicity against many economically important crops worldwide [1,2]. The main effects associated with the disease are the reduction in leaf photosynthetic activity and carbohydrate production, followed by separation of necrotic foliage from the taproot. These effects contribute to a significant reduction in the harvesting efficiency of infected carrots [7]. Molecules 2020, 25, x FOR PEER REVIEW metabolites, were wereconfirmed confirmedwith withthe theidentification identification aldaulactone a new phytotoxin involved in ofof aldaulactone as as a new phytotoxin involved in the the aggressiveness Given these findings, and of our aggressiveness of A.of dauci carrot cells [5].cells. As twophytotoxic additionalmetabolites lipophilic of α-acetylorcinol and p-hydroxybenzoic acid (2) as two additional lipophilic phytotoxic metabolites produced by the fungalproduced pathogen.by the fungal pathogen
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