Molecular Microbiology Research 2024, Vol.14, No.6, 259-270 http://microbescipublisher.com/index.php/mmr 259 Research Report Open Access Efficacy of Exogenous Melatonin Treatment of Leaf Spot Disease on Gardenia jasminoides Eills Caused byAternaria alternata Yangyang Ma 1,2,3, HanZhang1,2,3,YuluXie 1,2,3, Bizeng Mao1,2,3 1 Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, Zhejiang, China 2 Ministry of Agriculture Key Lab of Molecular Biology of Crop Pathogens and Insects, Hangzhou, 310058, Zhejiang, China 3 Key Laboratory of Biology of Crop Pathogens and Insects of Zhejiang Province, Hangzhou, 310058, Zhejiang, China Corresponding author: maobz@zju.edu.cn Molecular Microbiology Research, 2024, Vol.14, No.6 doi: 10.5376/mmr.2024.14.0028 Received: 20 Nov., 2024 Accepted: 30 Nov., 2024 Published: 07 Dec., 2024 Copyright © 2024 Ma et al., This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Ma Y.Y., Zhang H., Xie Y.L., and Mao B.Z., 2024, Efficacy of exogenous melatonin treatment of leaf spot disease on Gardenia jasminoides Eills caused by Aternaria alternata, Molecular Microbiology Research, 14(6): 259-270 (doi: 10.5376/mmr.2024.14.0028) Abstract Alternaria alternata is a common fungal species that can cause leaf spot disease in various plants. However, there is little information on Alternaria species causing leaf spot disease in Gardenia jasminoides. In the present study, six Alternaria spp. were isolated from symptomatic leaves of Gardenia jasminoides in Enshi, Hubei Province. Based on morphological characterization and molecular analyses, the six isolates were identified as Alternaria alternata. The pathogenicity test showed that these isolates were the causal agents of G. jasminoides leaf spot disease. Melatonin (N-acetyl-5-methoxytryptamine), which exists in all plant tissues and organs, plays a vital role in the plant response to abiotic and biotic stresses. However, the effect of melatonin on the prevention and treatment of Gardenia jasminoides leaf spot has not been reported. In this study, the ability of exogenous melatonin to reduce the pathogenic impact of A. alternata on G. jasminoides leaves was explored. The results demonstrated that 10 mM of melatonin had the most significant effect on the resistance of A. alternata on potato dextrose agar (PDA) plates, and 5.0 μM to 1.0 mM of melatonin effectively reduced the leaf lesion area of G. jasminoides. Overall, our results suggest that melatonin has good potential for application inG. jasminoides, enhancing resistance to leaf spot disease. Keywords Gardenia jasminoides; Alternaria alternata; Leaf spot disease; Resistance; Exgogenous melatonin 1 Introduction Gardenia jasminoides Ellis is a shrub in the Rubiaceae family. Its desiccative fruit, often called Zhizi in China, is used not only as a supereminent natural colorant but also as excellent traditional medicine for various ailments. This includes promoting blood circulation, eliminating stasis, clearing heat, and removing toxins. It is also used to treat diabetes and has anti-inflammatory, diuretic, antidepressant, and anticancer properties (Jin et al., 2023). G. jasminoides is native to China, Japan, India, and Thailand, and it is now widely grown in 16 provinces in China, especially along the Yangzi River (Chen et al., 2020). Among these provinces, Enshi in Hubei Province is the main production region; However, the warm and humid climate from May to July promotes the development of various diseases, resulting in large outbreaks of leaf spot disease, which seriously affect the yield of G. jasminoides. Leaf spot disease can be caused by various fungi, such as Alternaria (Liu et al., 2021a; Yang et al., 2022), Cercospora (Tan et al., 2023), Phyllosticta (Yang, 2023), Pestalotiopsis (Liu et al., 2021b), Fusarium oxysporum (Xue et al., 2023), Pseudocercospora (Crous et al., 2021), Cylindrocladium(Polizzi et al., 2006), Myrothecium (Mmbaga et al., 2010), and others. Among them, Alternaria spp. are the most common cause of fungal foliar diseases in vegetables, cereals, fruit trees, and medicinal plants during production and storage, resulting in field and post-production losses. Alternaria is a large ubiquitous dictyosporic genus, and the variability of the isolates within this genus is high even within the same species (Lawrence et al., 2013). Consequently, various approaches based on morphology, physiology, pathogenicity, and genetics have been proposed to establish identification and classification systems, but the resulting taxonomy remains unclear (Pryor et al., 2002; Andrew et al., 2009;
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