Insights into the Adaptation of Geotrichum citri-aurrantii in Highly Acidic Environments

Niu, Qian; Zheng, Jie; Liao, Wenbin; Qian, Ju; Tan, Xiaoli; Ouyang, Qiuli; Li, Lu; Tao, Nengguo

doi:10.3390/jof12020091

Open AccessArticle

Insights into the Adaptation of Geotrichum citri-aurrantii in Highly Acidic Environments

by

Qian Niu

^†,

Jie Zheng

^†,

Wenbin Liao

,

Ju Qian

,

Xiaoli Tan

,

Qiuli Ouyang

,

Lu Li

^*

and

Nengguo Tao

^*

School of Chemical Engineering, Xiangtan University, Xiangtan 411105, China

^*

Authors to whom correspondence should be addressed.

^†

These authors contributed equally to this work.

J. Fungi 2026, 12(2), 91; https://doi.org/10.3390/jof12020091

Submission received: 4 December 2025 / Revised: 7 January 2026 / Accepted: 26 January 2026 / Published: 29 January 2026

(This article belongs to the Section Environmental and Ecological Interactions of Fungi)

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Abstract

Sour rot is a significant postharvest disease affecting citrus fruit, causing sourness and decay in various cultivars, particularly lemons. How the pathogen, Geotrichum citri-aurantii, adapts to the highly acidic environment of citrus fruit remains inadequately understood. In this study, the growth characteristics, morphological and structural changes, gene expression profiles, and adaptive mechanisms of G. citri-aurantii under highly acidic conditions were elucidated. The findings indicated that G. citri-aurantii modified the environmental pH by either alkalizing (pH < 3.00) or acidifying (pH > 3.00) the host tissue. It exhibited strong adaptability at pH 2.2, showing shortened and aggregated hyphae, delayed spore germination, and increased vacuoles. Transcriptomic analysis and qRT-PCR identified the significant regulation of key differentially expressed genes involved in cell wall remodeling, cell membrane component synthesis, carbon metabolism, and signal transduction. These regulatory changes enable the pathogen to prevent an influx of external acids and maintain the energy supply under acid stress conditions. Additionally, the Pal/Rim pH signaling pathway genes exhibit distinct response patterns in citrus cultivars with different acidities. These findings enrich the comprehension of the pathogenic process of G. citri-aurantii and offer a theoretical foundation for preventing and managing citrus sour rot.

Keywords: acid tolerance; Geotrichum citri-aurantii; citrus fruit; Pal/Rim pH signaling pathway

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MDPI and ACS Style

Niu, Q.; Zheng, J.; Liao, W.; Qian, J.; Tan, X.; Ouyang, Q.; Li, L.; Tao, N. Insights into the Adaptation of Geotrichum citri-aurrantii in Highly Acidic Environments. J. Fungi 2026, 12, 91. https://doi.org/10.3390/jof12020091

AMA Style

Niu Q, Zheng J, Liao W, Qian J, Tan X, Ouyang Q, Li L, Tao N. Insights into the Adaptation of Geotrichum citri-aurrantii in Highly Acidic Environments. Journal of Fungi. 2026; 12(2):91. https://doi.org/10.3390/jof12020091

Chicago/Turabian Style

Niu, Qian, Jie Zheng, Wenbin Liao, Ju Qian, Xiaoli Tan, Qiuli Ouyang, Lu Li, and Nengguo Tao. 2026. "Insights into the Adaptation of Geotrichum citri-aurrantii in Highly Acidic Environments" Journal of Fungi 12, no. 2: 91. https://doi.org/10.3390/jof12020091

APA Style

Niu, Q., Zheng, J., Liao, W., Qian, J., Tan, X., Ouyang, Q., Li, L., & Tao, N. (2026). Insights into the Adaptation of Geotrichum citri-aurrantii in Highly Acidic Environments. Journal of Fungi, 12(2), 91. https://doi.org/10.3390/jof12020091

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Insights into the Adaptation of Geotrichum citri-aurrantii in Highly Acidic Environments

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