The drought resistance of different Camellia oleifera varieties at the seedling stage and their responses to drought stress were studied. The indexes suitable for the drought resistance evaluation and identification of Camellia oleifera were screened, and its drought resistance was comprehensively evaluated, in order to provide a theoretical basis and methods for the breeding of drought-resistant varieties of Camellia oleifera.

28 indexes such as morphology, growth, physiology and biochemistry of different Camellia oleifera varieties under drought stress were determined to study the drought resistance of different Camellia oleifera varieties. Principal component analysis was used to screen out the evaluation or identification indexes suitable for the drought resistance of Camellia oleifera. The drought resistance of Camellia oleifera varieties was comprehensively evaluated by subordinate function value analysis. According to the change of drought resistance coefficients of each index under different drought stress intensities, the response of different Camellia oleifera varieties to drought stress was studied and the drought resistance mechanism was discussed.

The results of the principal component analysis showed that 28 indexes related to drought resistance of Camellia oleifera were summarized into 3 principal components, and the cumulative contribution rate was 100%, which had strong information representation. The first principal component can be summarized as photosynthetic parameters and leaf anatomical parameters, the second principal component can be summarized as growth indexes, and the third principal component can be summarized as stomatal aperture and proline content. The corresponding drought resistance identification indicators were Pn, Gs, Tr, leaf thickness, upper epidermis thickness of leaves, stomatal aperture, stomatal density, dry matter accumulation, plant height growth and proline content. The drought resistance of 4 Camellia oleifera varieties was comprehensively evaluated by subordinate function value analysis, and the order of their drought resistance was Wu2 > Gan190 > Xing46 > Wu12. According to the changes in drought resistance coefficients of different Camellia oleifera varieties under 3 drought treatments, the responses of different Camellia oleifera varieties to drought stress were similar and had their own characteristics. Under drought stress, each Camellia oleifera variety mainly increased the number of lateral roots to improve the water absorption capacity of roots, and enhanced the resistance of plants by increasing the root-shoot ratio and root-to-plant ratio. The water loss was reduced and water use efficiency was improved by increasing leaf compactness, grid-sea ratio, stomatal density and WUE. By increasing the content of antioxidant SOD, the superoxide anion and other harmful substances could be removed to protect cell structures. By increasing the contents of soluble sugar, soluble protein and proline in leaves, the osmotic potential was reduced to regulate osmotic balance and reduce the damage of osmotic stress to plants. By increasing the contents of endogenous hormones such as ABA and MeJA, the drought resistance of Camellia oleifera was enhanced and the damage caused by drought stress was alleviated.

Pn, Gs, Tr, leaf thickness, leaf epidermis thickness, stomatal aperture, stomatal density, dry matter accumulation, plant height growth and leaf proline content can be used as drought resistance identification indexes of Camellia oleifera seedlings. By the comprehensive evaluation of drought resistance, Wu2 has the strongest drought resistance. The response of different Camellia oleifera varieties to drought stress is a multi-way joint response and drought resistance mechanism, which shows both similarities and characteristics. The response of each variety under mild drought stress is different, but under severe drought stress, it is a multi-way joint response mechanism mainly dominated by SOD or ABA.

The differences of fruit traits, seed traits and rootstock traits among different Camellia oleifera varieties were studied, and the correlation between the indexes of fruit, seed and rootstock traits was analyzed, so as to provide theoretical basis for the breeding of excellent rootstocks of C. oleifera.

The 18 indexes of fruit traits, seed traits and rootstock traits of different C. oleifera varieties were determined. The differences of fruit, seed and rootstock traits among different C. oleifera varieties were studied by one-way analysis of variance, and the C. oleifera varieties with better comprehensive performance were selected. The correlation between 18 indexes was obtained by correlation analysis, and the indexes with strong correlation with rootstock traits were selected to provide theoretical basis for the selection of excellent rootstocks.

The results of one-way ANOVA showed that there were significant differences in single fruit mass, fruit longitudinal diameter, fruit transverse diameter, fruit aspect ratio, peel thickness, fruit seed number and seed mass among different C. oleifera varieties. The single fruit mass of 22 C. oleifera varieties ranged from 15.71 to 35.99 g, the fruit longitudinal diameter was 29.81-40.17 mm, the fruit transverse diameter was 29.06-39.99 mm, the fruit shape index was 0.85-1.28, the peel thickness was 1.85-4.19 mm, and the fruit seed number was 2.20-9.67. There were significant differences in single seed mass, seed longitudinal diameter, seed transverse diameter, seed lateral diameter, ratio of longitudinal diameter to transverse diameter, ratio of transverse diameter to lateral diameter and ratio of longitudinal diameter to lateral diameter among different C. oleifera varieties. The single seed mass of 22 C. oleifera varieties ranged from 1.07 to 4.26 g, the seed longitudinal diameter ranged from 16.98 to 27.40 mm, the seed transverse diameter ranged from 13.17 to 23.12 mm, and the seed lateral diameter ranged from 9.00 to 16.93 mm. There were significant differences in epicotyl length, hypocotyl length, epicotyl diameter and hypocotyl diameter among different C. oleifera varieties. The epicotyl length of 22 C. oleifera varieties ranged from 5.38 to 9.08 cm, epicotyl diameter ranged from 1.72 to 2.97 mm, hypocotyl length ranged from 14.35 to 23.97 cm, and hypocotyl diameter ranged from 1.80 to 3.14 mm. The results of correlation analysis showed that the correlation between epicotyl length and fruit transverse diameter, single seed mass, seed lateral diameter and fruit longitudinal diameter was significant. The correlation between hypocotyl length and seed longitudinal diameter, seed lateral diameter, fruit longitudinal diameter and fruit seed number was significant. The epicotyl thickness was significantly positively correlated with single fruit mass, fruit longitudinal diameter, single seed mass, seed longitudinal diameter, seed transverse diameter and seed lateral diameter. The hypocotyl thickness was significantly positively correlated with fruit aspect ratio and fruit longitudinal diameter.

Based on the indexes of fruit, seed and rootstock traits, the C. oleifera varieties suitable for excellent rootstocks were selected as GW 2, GS 83-4, CL 53 and GLSGZY 1. The correlation analysis showed that the four indexes of the rootstock traits were significantly positively correlated with the fruit longitudinal diameter or the correlation was large. Therefore, the fruit with relatively large fruit longitudinal diameter could be selected from the above four C. oleifera varieties suitable for excellent rootstocks for rootstock cultivation.