Detection and Fitness of Dicarboximide-Resistant Isolates of Alternaria alternata from Dendrobium officinale, a Chinese Indigenous Medicinal Herb

Abstract

Black spots caused by Alternaria Alternata poses a sever threat to the industry of Dendrobium officinale, a Chinese indigenous medicinal herb. Dicarboximide fungicides (DCFs) are intensively used to control this disease for decades in China, and offering excellent efficacy. The resistance of phytopathogenic pathogens against DCFs are reportedly selected in fields; however, the DCF-resistance of A. alternata from D. officinale is not well understood. The low procymidone-resistant (ProLR) isolates of A. alternata were detected in the commercial orchards of D. officinale in China in 2018 and biochemically characterized in this study. The result showed that the low procymidone-resistant (ProLR) isolates were selected in the commercial orchards with the resistance frequency of 100 %, and no significant difference in mycelial growth, sporulation and virulence was observed among the ProLR and ProS isolates. A positive cross-resistance pattern was exhibited between procymidone and iprodione. Amino acid sequence alignment results of AaOS-1 from the tested isolates showed that all the ProLR genotypes could be categorized into two groups, including group I (mutations at AaOs-1) and group II (no mutation). On procymidone (5.0 μg/ml) treatment condition, the AaOs-1 expression levels increased in the ProS isolates ranged from 2.94~3.69 folds higher than those on procymidone-free condition, while the AaOs-1 expressions of the ProLR isolates were significantly lower than those in the ProS isolates on the same conditions. The data indicated that the mutations at AaOs-1 are involved in the DCF-resistance of A. alternata selected in the D. officinale orchards.

Illumina-Based Analysis Yields New Insights Into the Fungal Contamination Associated With the Processed Products of Crataegi Fructus

“…The study performed by Pickova et al showed that the quality of Milk Thistle, which is an herb used for treatment of liver disease, was affected by fungi in Alternaria and their mycotoxins ( 33 ). Zhao et al also indicated that fungal strains in Alternaria severely threatened the industry of Dendrobium officinale ( 34 ). Furthermore, several Alternaria species were not only considered as spoilage agents for herbs but were also capable of synthesizing some mycotoxins such as alternariol, alternariol monomethyl ether, and altenuene, causing damage to human health ( 35 ).…”

The HOG‐pathway related AaOS1 leads to dicarboximide‐resistance in field strains of Alternaria alternata and contributes, together with the Aafhk1, to mycotoxin production and virulence

“…To date, five classes of fungicides have been registered to control the GLS caused by A. alternata , including dicarboximides, phenylpyrroles, sterol demethylation inhibitors (DMIs), quinone outside inhibitor (QoIs) and succinate dehydrogenase inhibitors (SDHIs). However, populations of A. alternata isolated from passionfruit, 2 radish, 5 pistachio, 13–15 dendrobium officinale, 16 cabbage and broccoli 17 are reported to be resistant to the above‐described five classes of fungicides. The modes‐of‐action (MoAs) of DMIs, 13 QoIs 18 and SDHIs 18 have been elucidated, but the targets of dicarboximide and phenylpyrroles fungicides are not.…”