Drought Resistance Evaluation of Camellia oleifera var. "Xianglin 210" Grafted onto Different Rootstocks

Abstract

As a key economic tree in southern China, Camellia oleifera faces severe yield losses under drought. Grafting onto drought-tolerant rootstocks offers a potential mitigation strategy. To elucidate the impact of rootstocks on the drought resistance of the superior Camellia oleifera Abel. cultivar "Xianglin 210", grafted seedlings with five scion-rootstock combinations, were subjected to gradient drought stress. Key physiological and biochemical indices related to photosynthesis, antioxidant enzymes, and osmotic adjustment were measured. Drought resistance was comprehensively evaluated using membership function analysis, and the expression of stress-responsive genes was quantified via quantitative real-time PCR (qRT-PCR). The results demonstrated that under drought stress, (1) stomatal conductance (Gs) decreased by 31.2-48.7%, while instantaneous water use efficiency (WUE) increased by 18.5-35.4%; (2) proline (Pro) and soluble sugars (SS) accumulated significantly, with increases of 2.3-4.1-fold and 1.8-3.2-fold, respectively; (3) activities of antioxidant enzymes were enhanced by 56-127%, mitigating oxidative damage; (4) membership function analysis ranked drought resistance as follows: Xianglin 27 (0.812) > Guangxi Superior Germplasm (0.698) > C. yuhsienensis (0.654) > Hunan Superior Germplasm (0.591) > Xianglin 1 (0.523); (5) qRT-PCR revealed significant upregulation of ABA signaling pathway genes (CoPYL6, CoPP2C75/51/24/26, CoSnRK2.8, and CoABI5) and transcription factors (CoLHY and CoWRKY70), indicating activation of drought-responsive regulatory networks. These findings provide a theoretical foundation for selecting drought-tolerant rootstocks and optimizing cultivation practices in Camellia oleifera, and provide practical criteria for selecting drought-tolerant rootstocks, facilitating sustainable Camellia oleifera cultivation in water-limited regions.

Keywords: Camellia oleifera; comprehensive evaluation; drought stress; gene expression.

Figure 1

Effects of different soil moisture content on five different rootstock C. oleifera grafting combinations Pn (A), Gs (B), Ci (C), Tr (D), Fv/Fm (E), and WUE (F). Different uppercase letters indicate significant differences in the mean values of different combinations under the same soil moisture content (p < 0.05), and different lowercase letters indicate significant differences in the mean values of the same combination under different soil moisture contents (p < 0.05). T1, T2, T3—soil moisture treatments corresponding to 6, 8, and 10 days of water withholding, respectively; C1, C2, C3, C4, C5—different rootstock–scion grafting combinations (see Table 1 for details). Pn—net photosynthetic rate; Gs—stomatal conductance; Ci—intercellular CO₂ concentration; Tr—transpiration rate; WUE—water use efficiency; Fv/Fm—theoretical maximum photochemical efficiency.

Figure 2

Effects of different soil moisture content on five different rootstock C.a oleifera grafting combinations: Pro (A), TP (B), SS (C), and MDA (D). Different uppercase letters indicated significant differences in the mean values of different combinations under the same soil moisture content (p < 0.05), and different lowercase letters indicated significant differences in the mean values of the same combinations under different soil moisture contents (p < 0.05). T1, T2, T3—Soil moisture treatments corresponding to 6, 8, and 10 days of water withholding, respectively; C1, C2, C3, C4, C5—different rootstock–scion grafting combinations (see Table 1 for details). MDA—malondialdehyde; Pro—proline; SS—soluble sugars; TP—total phosphorus.

Figure 3

Effects of different soil moisture content on five different rootstock C. oleifera grafting combinations: SOD (A), POD (B), CAT (C), and GSH (D). Different uppercase letters indicated significant differences in the mean values of different combinations under the same soil moisture content (p < 0.05), and different lowercase letters indicated significant differences in the mean values of the same combinations under different soil moisture contents (p < 0.05). T1, T2, T3—soil moisture treatments corresponding to 6, 8, and 10 days of water withholding, respectively; C1, C2, C3, C4, C5—different rootstock–scion grafting combinations (see Table 1 for details). SOD—superoxide dismutase; POD—peroxidase; CAT—catalase; GSH—reduced glutathione.

Figure 4

Effects of different soil moisture contents on the expression levels of five combinations of CoRbcL (A), CoLHY (B), CoGI (C), CoGATA8 (D) and CoWRKY70 (E). Vertical bars indicate standard deviation of the mean (n = 3). T1, T2, T3—soil moisture treatments corresponding to 6, 8, and 10 days of water withholding, respectively; C1, C2, C3, C4, C5—different rootstock–scion grafting combinations (see Table 1 for details).

Figure 5

Effects of different soil water contents on the expression levels of CoPYL6 (A), CoPP2C16 (B), CoPP2C24 (C), CoPP2C51 (D), CoPP2C75 (E), CoSnRK2.8 (F), CoABI5 (G), and CoSAUR32 (H) in five combined grafting seedlings. Vertical bars indicate standard deviation of the mean (n = 3). T1, T2, T3—soil moisture treatments corresponding to 6, 8, and 10 days of water withholding, respectively; C1, C2, C3, C4, C5—different rootstock–scion grafting combinations (see Table 1 for details).