In this study, we compared the differences in pulp disease resistance between two melon cultivars, Karakokouqi (KKQ), a specialty cultivar in southern Xinjiang, and Xizhoumi 25 (XZM) as a control. To this end, melons were artificially wounded and inoculated with Fusarium equiseti before refrigerated storage. The results showed that during the whole storage period, XZM underwent respiratory climacteric, while KKQ did not. The onset of Fusarium rot was 5 day later in KKQ than in XZM, and the diameter and depth of rotten spots on the 25th day of infection were 1.26 and 1.19 times higher in XZM than in KKQ, respectively. During the infection period, the expression of the chitinase (CHT) and β-1,3-glucanase (GLU) genes was always higher in KKQ than in XZM, and the relative expression levels of CmGLU, CmCHT1 and CmCHT2 were high on the 5th day, indicating that the expression of resistance protein genes was rapidly induced in KKQ after pathogen infection. CHT and GLU activities tended to increase and then decrease with storage time, and were higher in KKQ than in XZM, indicating that disease resistance in KKQ was closely related to the activities and gene expression of CHT and GLU. The relative expression levels of the ethylene synthesis-related genes CmACS1, CmACS2, and CmACO1 were higher in XZM than in KKQ, and the relative expression levels of the ethylene receptor genes CmETR1 and CmERS1 were significantly higher in KKQ than in XZM, indicating that the ethylene receptor genes negatively regulated ethylene synthesis. Correlation analysis showed that the diameter of the infection lesions on XZM was highly significantly positively correlated with the ethylene receptor genes, suggesting that elevated ethylene-related enzyme activities and gene expression accelerated Fusarium infection in XZM. Thus, elevated disease resistance-related enzyme activities and gene expression hindered infection of KKQ by pathogenic fungi, whereas elevated ethylene-related enzyme activities and gene expression accelerated infection of XZM by pathogenic fungi.

In order to explore the structure and dynamic changes of fungal communities in melon fruit during storage, the internal transcribed spacer (ITS) region of fungi in melon peel and pulp stored for 0, 7, 14, or 21 d was sequenced using Illumina MiSeq high-throughput sequencing technology. Species annotation and species composition analysis were used to determine the dominant fungal communities in the fruit tissues at each storage time point. The results showed that Vishniacozyma, Papiliotrema, and Metarhizium were dominant in the peel on day 0, while Aspergillus, Trichothecium, and Penicillium became dominant as storage time increased. The dominant fungal communities in the flesh also changed as storage time increased, with Vishniacozyma, Trichothecium, and Pichia being the dominant fungi on the 21^th day of storage. Diversity analysis showed that fungal abundance and diversity were higher in the peel than in the flesh. In summary, the abundance and diversity of fungal communities in melon tissues changed significantly during storage, and the interaction of pathogenic fungi such as Aspergillus, Trichothecium, and Penicillium resulted in deterioration of melon fruit quality. This study provides a theoretical basis for the development of preservation methods and biological control strategies for melons in the future.