Yulin Cheng et al., Microorganisms
As the major postharvest disease of citrus fruit, postharvest green mold is caused by the necrotrophic fungus Penicillium digitatum (Pd), which leads to huge economic losses worldwide.
Fungicides are still the main method currently used to control postharvest green mold in citrus fruit storage.
Investigating molecular mechanisms of plant–pathogen interactions, including pathogenicity and plant resistance, is crucial for developing novel and safer strategies for effectively controlling plant diseases.
Despite fruit–pathogen interactions remaining relatively unexplored compared with well-studied leaf–pathogen interactions, progress has occurred in the citrus fruit–Pd interaction in recent years, mainly due to their genome sequencing and establishment or optimization of their genetic transformation systems.
Recent advances in Pd pathogenicity on citrus fruit and fruit resistance against Pd infection are summarized in this review, arranged through the following index:
2. Infection Characteristics of Pd on Citrus Fruit
2.1. Infection Process
2.2. Influence Factors of Pd Spore Germination
2.3. Mycotoxin during Pd Infection
3. Pathogenic Mechanisms of Pd
3.1. Transcription Factors in Pd Pathogenicity
3.2. Cell Wall-Related Enzymes in Pd Pathogenicity
3.3. Protein Kinases in Pd Pathogenicity
3.4. Transporters in Pd Pathogenicity
3.5. Other Genes in Pd Pathogenicity
4. Fruit Resistance against Pd Infection
4.1. Reactive Oxygen Species and Nitric Oxide in Citrus Fruit Resistance
4.2. Plant Metabolism in Citrus Fruit Resistance
4.3. Resistance Mediated by Other Fruits
5. Open Questions
5.1. What Are the Roles of Virulence-Associated Effectors in Pd Pathogenicity?
5.2. Can the Revolutionary Genome Editing Biotechnology Be Used to Generate Citrus Varieties Resistant to Postharvest Green Mold?
Postharvest fungal diseases on fruit have received increased attention from researchers in different fields mainly including horticulture, plant protection, and food science. Synthetic fungicides, which have noticeable health or environmental risks, are still the main method used to control them in current fruit storage.
Although many nonchemical treatments, mainly including biocontrol agents, natural compounds, UV, hot water treatment, and salts have been used for controlling postharvest fungal diseases on fruit [142,143], these diseases still lead to huge economic losses worldwide every year.
Increasing evidence reveals that investigating molecular mechanisms of plant–pathogen interactions is essential for developing novel and safer strategies for durably controlling plant diseases.
Thus, this review focused on recent advances in the citrus fruit–Pd interaction, providing significant insights into fruit–pathogen interactions and is beneficial for developing novel and safer strategies for controlling citrus postharvest green mold.
A total of 19 Pd genes mainly encoding transcription factors, cell wall-related enzymes, protein kinases, and transporters are required for Pd pathogenicity. Of these Pd pathogenicity factors, PdChsVII and PdGcs1 are ideal targets for new drugs to control citrus postharvest green mold. Whether HIGS or SIGS of Pd pathogenicity factors can be used to control citrus postharvest green mold remains to be investigated.
In addition, several fruit resistance responses, including ROS, NO, secondary metabolites, and primary metabolites, are involved in citrus fruit resistance against Pd interaction. No other citrus gene has yet been reported to regulate citrus fruit resistance.
Identification and functional analysis of citrus genes that regulate citrus fruit resistance against Pd infection will be conducted using transgenesis or genome editing.
Citrus Postharvest Green Mold: Recent Advances in Fungal Pathogenicity and Fruit Resistance
Yulin Cheng, Yunlong Lin, Haohao Cao, and Zhengguo Li
Microorganisms 2020 Mar; 8(3): 449.
Published online 2020 Mar 23. doi: 10.3390/microorganisms8030449