This study comprehensively investigates the physiological and molecular regulatory mechanisms of Camellia oleifera seedlings under drought stress with a soil moisture content of about 30%, where exogenous abscisic acid (ABA) was applied via foliar spraying at concentrations of 50 µg/L, 100 µg/L, and 200 µg/L. The results demonstrated that appropriate concentrations of ABA treatment can regulate the physiological state of the seedlings through multiple pathways, including photosynthesis, oxidative stress response, and osmotic balance, thereby aiding in the restructuring of their drought response strategy. ABA treatment effectively activated the antioxidant system by reducing stomatal conductance and moderately inhibiting the photosynthetic rate, thus alleviating oxidative damage caused by drought stress. Additionally, ABA treatment promoted the synthesis of osmotic regulators such as proline, maintaining cellular turgor stability and enhancing the plant’s drought adaptability. The real-time quantitative PCR results of related genes indicated that ABA treatment enhanced the plant’s response to the ABA signaling pathway and improved disease resistance by regulating the expression of related genes, while also enhancing membrane lipid stability. A comprehensive evaluation using a membership function approach suggested that 50 µg/L ABA treatment may be the most-effective in mitigating drought effects in practical applications, followed by 100 µg/L ABA. The application of 50 µg/L ABA for 7 h induced significant changes in various biochemical parameters, compared to a foliar water spray. Notably, superoxide dismutase activity increased by 17.94%, peroxidase activity by 30.27%, glutathione content by 12.41%, and proline levels by 25.76%. The content of soluble sugars and soluble proteins rose by 14.79% and 87.95%, respectively. Additionally, there was a significant decrease of 31.15% in the malondialdehyde levels.

Oil tea camellia (Camellia spp.) is an important woody oil crop with a high nutritional and economic value. Whole-genome resequencing (WGR) technology can provide an in-depth understanding of the genetic background of this plant as well as a reference for breeding research, germplasm resource conservation, and genetic modification. In this study, we analyzed SNP and InDel variations in 49 individual oil tea camellia germplasm samples collected from five populations located in three provinces of China: Hainan, Guangdong and Guangxi. The samples were analyzed through WGR after the ploidy of the samples was determined through flow cytometry. A total of 239,441,603 high-quality single nucleotide polymorphisms (SNPs) and 23,510,374 high-quality insertion/deletion variation sites (InDels) were obtained. The distribution of SNPs and InDels in different functional regions differed significantly, with a high density of variations in non-coding regions, such as intergenic regions and introns, and a relatively low density of variations in coding regions. Transition was the main type of SNP variation. A population genetic diversity analysis revealed that the sampled oil tea camellia populations exhibited a high genetic diversity and extensive genetic variation. The genetic diversity of the oil tea camellia populations in the Hainan region was higher than inland regions. This study also determined the genetic diversity of and variations between octoploid and decaploid oil tea camellia in the tropics and between Hainan-based and inland oil tea camellia. Such findings provide a reference for the conservation of germplasm resources and the genetic modification of oil tea camellia.

Camellia oleifera C. Abel is a woody oil crop with multiple purposes. This study aims to investigate the mutagenic effects of ⁶⁰Co-γ radiation on C. oleifera seedlings and to screen anthracnose-resistant mutants. Two C. oleifera varieties were investigated: ‘Xianglin 1’ (XL1) and ‘Xianglin 210’ (XL210). Seeds were irradiated with 0 Gy, 30 Gy, 50 Gy, and 80 Gy of ⁶⁰Co-γ, and after one year of planting, the mutagenic lines were studied, and disease-resistant mutants were screened. Results showed that as the radiation intensity was increased, the emergence percentage of both C. oleifera XL210 and XL1 was significantly decreased. Radiation significantly changed the SOD and POD activities in both varieties. Furthermore, 80 Gy irradiated lines showed reduced anthracnose resistance in both varieties. However, 50 Gy irradiated lines showed enhanced disease resistance in XL210 while reducing it in XL1. The 30 Gy irradiated lines did not affect the disease resistance of either variety. Colletotrichum gloeosporioides infection tests were conducted on 94 mutant C. oleifera seedlings, resulting in 8 highly resistant mutants (A3, A8, A10, A19, A21, A32, A35, B17) and 3 susceptible mutants (A4, B15, B27) in XL210 and XL1. Differences in SOD and POD activities led to variations in disease resistance among different mutants. Additionally, the expression levels of CoSOD1, CoPOD, CoIDD4, and CoWKRY78 were varied among the different mutants. This study delivers the screening of disease-resistant mutants in C. oleifera through mutagenic breeding, providing material for the development of new C. oleifera varieties and serving as a resource for further research in mutagenic breeding.