Postharvest apple immunity: a key factor in shelf life and fruit quality

Postharvest losses in fruits, particularly apples, are a significant global issue. New research sheds light on how the immune system of apple fruits interacts with their microbiomes during storage, playing a crucial role in maintaining fruit health and preventing spoilage. By investigating the dynamics of the apple microbiota and immune gene expression during postharvest storage, researchers have uncovered a temporal shift in microbial communities that correlates with a decline in the fruit's immune response, suggesting a direct link between immune collapse and the growth of spoilage microbes. This study paves the way for novel strategies to enhance fruit preservation.

The microbiome of fruit, which includes beneficial microbes that contribute to fruit health, undergoes significant changes postharvest, especially as fruits age. Understanding how these shifts in the microbiome, coupled with changes in immune gene expression, lead to decay could provide insights into prolonging fruit shelf life. In particular, the plant immune system, which governs the microbiome, has been implicated in maintaining a healthy balance of microbes on the fruit surface. However, little is known about how the immune system of apples functions after harvest. This research highlights the importance of immune responses in fruit preservation. Based on these challenges, or due to these issues, there is a need for deeper studies into how postharvest treatments can strengthen fruit immunity.

The study, conducted by researchers at Michigan State University and Duke University, was published (DOI: 10.1093/hr/uhaf063) in Horticulture Research in February 2025. The researchers explored the interactions between the apple fruit microbiome and its immune system during storage. They found that, as fruit ages, the immune response weakens, allowing spoilage microbes like Alternaria and Gluconobacter to thrive, causing decay. Interestingly, artificially boosting the immune response with a peptide (flg22) delayed the onset of rot, suggesting that strengthening immune defenses could be a valuable strategy for improving postharvest fruit health.

Using a combination of microbial sequencing and gene expression analysis, the study tracked the fungal and bacterial community shifts on apple skin and pulp during postharvest storage. It revealed that, over time, the diversity of beneficial microbes like Sporobolomyces decreased, while pathogens like Alternaria increased. The study also examined key immune-related genes, such as MdFLS2 and MdBAK1, whose expression significantly decreased as fruits aged, coinciding with the appearance of spoilage. Moreover, when the fruit's immune response was artificially triggered with flg22, it delayed the development of fungal rot caused by Penicillium expansum. This finding highlights the potential of immuno-boosting treatments for extending shelf life and preventing fruit decay.

"Understanding the relationship between the fruit immune system and its microbiome during storage is critical for improving postharvest fruit health," said Dr. George Sundin, co-author of the study. "Our research shows that the immune response, which normally helps maintain a healthy microbial balance, weakens over time, leading to fruit decay. This suggests that enhancing immunity could be a key strategy for reducing postharvest losses."

These findings open the door to innovative approaches for reducing food waste by extending the shelf life of fruits. By manipulating the immune systems of apples, it may be possible to prevent the onset of decay and maintain fruit quality for longer periods, benefiting both producers and consumers. Further research could explore similar strategies for other fruits and vegetables, potentially leading to more sustainable postharvest management practices across the food industry.

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References

DOI

10.1093/hr/uhaf063

Original Source URL

https://doi.org/10.1093/hr/uhaf063

Funding information

Hannah McMillan is supported by a Postdoctoral Fellowship in Biology from the National Science Foundation (Award Number 2208939). Sheng Yang He is an investigator at Howard Hughes Medical Institute. Roselane Kithan-Lundquist was supported by a fellowship from the US National Institutes of Health Plant Biotechnology for Health and Sustainability Training Program at Michigan State University (Grant nos: NIH T32-GM110523).

About Horticulture Research

Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.