Identification of Colletotrichum aenigma as the new causal agent of leaf blight disease on Aucuba japonica Thunb., and screenings of effective fungicides for its sustainable management

Ruidong Fan; Yanjiang Liu; Yalan Bin; Jingyi Huang; Benlin Yi; Xiaoli Tang; Yingxue Li; Yu Cai; Ziyan Yang; Mingxuan Yang; Jiahao Song; Qi Pan; Zengliang Liu; Muhammad Imran Ghani; Xiaojing Hu; Xiaoyulong Chen

doi:10.3389/fmicb.2023.1222844

Identification of Colletotrichum aenigma as the new causal agent of leaf blight disease on Aucuba japonica Thunb., and screenings of effective fungicides for its sustainable management

Front Microbiol. 2023 Aug 24:14:1222844. doi: 10.3389/fmicb.2023.1222844. eCollection 2023.

Authors

Ruidong Fan^{1

2

3}, Yanjiang Liu^{2

3

4}, Yalan Bin^{1

2

3}, Jingyi Huang^{1

2

3}, Benlin Yi^{1

2

3}, Xiaoli Tang^{1

2

3}, Yingxue Li^{1

2

3}, Yu Cai^{1

2

3}, Ziyan Yang^{1

2

3}, Mingxuan Yang^{1

2

3}, Jiahao Song^{1

2

3}, Qi Pan^{1

2

3}, Zengliang Liu⁵, Muhammad Imran Ghani^{1

2

3}, Xiaojing Hu^{1

2

3}, Xiaoyulong Chen^{1

2

3

4}

Affiliations

¹ College of Agriculture, College of Life Sciences, Guizhou University, Guiyang, China.
² International Jointed Institute of Plant Microbial Ecology and Resource Management in Guizhou University, Ministry of Agriculture, China Association of Agricultural Science Societies, Guiyang, China.
³ Guizhou-Europe Environmental Biotechnology and Agricultural Informatics Oversea Innovation Center in Guizhou University, Guizhou Provincial Science and Technology Department, Guiyang, China.
⁴ School of Ecology and Environment, Tibet University, Lhasa, China.
⁵ Microbiology Research Institute, Guangxi Agricultural Science Academy, Nanning, China.

Abstract

Aucuba japonica Thunb is an evergreen woody ornamental plant with significant economic and ecological values. It also produces aucubin, showing a variety of biological activities. It is widely planted in the southwest region of China, including karst landscape areas in Guizhou Province. In January 2022, a serious leaf blight disease was observed on the leaves of A. japonica in the outdoor gardens of Guizhou University, Guiyang, Guizhou, China. The causal agent was identified as Colletotrichum aenigma through amplification and sequencing of the internal transcribed spacer (ITS) region, translation of the chitin synthase (CHS) and actin (ACT) genes, and morphological characterizations. Koch's postulates were confirmed by its pathogenicity on healthy leaves, including re-isolation and identification. To our knowledge, this is the first report of C. aenigma causing leaf blight on A. japonica worldwide. To identify pathogen characteristics that could be utilized for future disease management, the effects of temperature and light on mycelial growth, conidia production, and conidial germination, and the effects of humidity on conidial germination were studied. Optimal temperatures for mycelial growth of C. aenigma BY827 were 25-30°C, while 15°C and 35°C were favorable for conidia production. Concurrently, alternating 10-h light and 14-h dark, proved to be beneficial for mycelial growth and conidial germination. Additionally, conidial germination was enhanced at 90% humidity. In vitro screenings of ten chemical pesticides to assess their efficacy in suppressing C. aenigma representative strain BY827. Among them, difenoconazole showed the best inhibition rate, with an EC₅₀ (concentration for 50% of maximal effect) value of 0.0148 μg/ml. Subsequently, field experiment results showed that difenoconazole had the highest control efficiency on A. japonica leaf blight (the decreasing rate of disease incidence and decreasing rate of disease index were 44.60 and 47.75%, respectively). Interestingly, we discovered that C. aenigma BY827 may develop resistance to mancozeb, which is not reported yet among Colletotrichum spp. strains. In conclusion, our study provided new insights into the causal agent of A. japonica leaf blight, and the effective fungicides evaluated provided an important basis and potential resource for the sustainable control of A. japonica leaf blight caused by C. aenigma in the field.

Keywords: Aucuba japonica; Colletotrichum aenigma; agroecological disease; fungicides screening and resistance; leaf blight.