Abstract:

Objective: This study aims to investigate the effect of witches’ broom disease on the hydraulic architechture and carbon metabolism of jujube trees to reveal the pathophysiological mechanism of witches’ broom disease, so as to provide a theoretical basis for the formulation of targeted management measures. Method: The healthy, mild diseased and severe diseased Ziziphus jujuba cv. ‘Huping’ trees were used as the research object. The maximum hydraulic conductivity (K_max), hydraulic vulnerability to embolism (P₅₀), and morphological and anatomical characteristics of the jujube branches and leaves were measured. The water potential, branch percentage loss of conductivity (PLC), gas exchange parameters and nonstructural carbohydrates (NSC) contents of the three types of jujube trees in winter-spring period (November to April of the following year) and growing season (June) were also compared. Result: With the aggravation of the disease, the K_max of the jujube branches and leaves significantly decreased, and the P₅₀ of the branches and leaves significantly increased. The branch K_max of mild and severe diseased jujube trees was reduced by 40.75% and 80.61%, and the leaf K_max of mild and severe diseased jujube trees was reduced by 12.25% and 29.44%, respectively, compared to that of healthy jujube trees. The branch P₅₀ of mild and severe diseased jujube trees increased by 0.18 MPa and 0.63 MPa, and the leaf P₅₀ of mild and severe diseased jujube trees increased by 0.15 MPa and 0.31 MPa, respectively, compared to that of healthy jujube trees. With the aggravation of the disease, the thickness of vessel wall and collapse resistance index of the branches decreased significantly, and the wood density and vessel diameter of the branches of the severe diseased trees were significantly lower than those of the healthy ones. During winter-spring period and growing season, with the aggravation of the disease, branch PLC increased significantly, and phloem water content, phloem cell viability, and NSC content in phloem and xylem of branches decreased significantly. The photosynthetic rate, stomatal conductance and transpiration rate of leaves decreased significantly in the growing season, with photosynthetic rate of leaves of mild and severe diseased jujube trees being reduced by 12.25% and 29.44% compared to that of healthy jujube trees, respectively. Conclusion: The decrease in maximum hydraulic conductivity of leaves and branches is mainly related to the decrease of vessel diameter, and the decrease in hydraulic safety is mainly related to the decrease of vessel wall thickness, vessel collapse resistance and wood density, which may be caused by insufficient carbon supply. The decrease in water transport capacity and safety affects the water status of trees in the winter-spring period and growing seasons, limiting photosynthesis and resulting in carbon limitation, which further constrains the growth and the adaptability of jujube trees to adversity. Hydraulic limitation and carbon limitation are an important reason for the poor growth and dieback of diseased jujube trees.

Key words: witches’ broom disease, hydraulic traits, anatomic structure, nonstructural carbohydrates