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The plant cuticle is the outermost layer of the aerial organs and an important barrier against biotic and abiotic stresses. The climate varies greatly between the north and south of China, with large differences in temperature and humidity, but Chinese chestnut is found in both regions. This study investigated the relationship between the wax layer of chestnut leaves and environmental adaptation. Firstly, semi-thin sections were used to verify that there is a significant difference in the thickness of the epicuticular wax layer between wild chestnut leaves in northwest and southeast China. Secondly, a whole-genome selective sweep was used to resequence wild chestnut samples from two typical regional populations, and significant genetic divergence was identified between the two populations in the CmCER1-1, CmCER1-5 and CmCER3 genes. Thirty-four CER genes were identified in the whole chestnut genome, and a series of predictive analyses were performed on the identified CmCER genes. The expression patterns of CmCER genes were classified into three trends—upregulation, upregulation followed by downregulation and continuous downregulation—when chestnut seedlings were treated with drought stress. Analysis of cultivars from two resource beds in Beijing and Liyang showed that the wax layer of the northern variety was thicker than that of the southern variety. For the Y-2 (Castanea mollissima genome sequencing material) cultivar, there were significant differences in the expression of CmCER1-1, CmCER1-5 and CmCER3 between the southern variety and the northern one-year-grafted variety. Therefore, this study suggests that the CER family genes play a role in environmental adaptations in chestnut, laying the foundation for further exploration of CmCER genes. It also demonstrates the importance of studying the adaptation of Chinese chestnut wax biosynthesis to the southern and northern environments. [ABSTRACT FROM AUTHOR]

Castanea species have enormous potential for broad applications in the biomedical sciences and chemical wood industries. Due to the occurrence of fungal diseases, especially chestnut blight, the survival status of Castanea plants is seriously threatened. Castanea plants in China have natural tolerance to chestnut blight. This study investigated the genetic diversity and chestnut blight resistance of Castanea plants in China and searched for germplasm with high tolerance resistance. Cluster and population structure analysis revealed that wild Castanea plants in China could be divided into three groups with significant interspecific boundary, C. henryi var. omeiensis is located between C. mollissima and C. henryi var. henryi. The ABBA-BBAA test showed that significant gene introgression occurred between C. mollissima and C. henryi in Mount Emei, supporting the conclusion that C. henryi var. omeiensis as a natural hybrid resource. The results of disease resistance evaluation showed that the tolerance of wild C. mollissima to chestnut blight was the highest and significantly higher than that of wild C. henryi and C. seguinii. In particular, there is a strong association between disease tolerance in C. henryi var. omeiensis and the level of genetic introgression from C. mollissima. Then, the rIBD fragments of C. henryi var. omeiensis derived from C. mollissima were analyzed to reveal the source of disease resistance using whole genome resequencing data. A total of 203 rIBD segments containing 435 genes were identified. Finally, 41 candidate genes for chestnut blight resistance were selected through multiple omics. In conclusion, this study investigated a type of interspecific disease-resistant hybrid resources, identified a set of candidate genes for chestnut blight resistance, and provided new strategies for disease-resistant breeding of chestnut resources in the future. • The tolerance of wild Castanea including three species to chestnut blight in China was evaluated. • It was confirmed that C. henryi var. omeiensis was an interspecific hybrid with high tolerance to chestnut blight. • A total of 203 rIBD segments and 41 candidate disease resistance genes were identified to enable next-generation precision breeding of chestnuts. [ABSTRACT FROM AUTHOR]