Physiological Response Mechanism and Drought Resistance Evaluation of Passiflora edulis Sims under Drought Stress

In order to explore the response mechanism of Passiflora edulis Sims to drought stress, the changes in morphological and physiological traits of Passiflora edulis Sims under different drought conditions were studied. A total of 7 germplasm resources of Passiflora edulis Sims were selected and tested under drought stress by the pot culture method under 4 treatment levels: 75%-80% (Control, CK) of maximum field water capacity, 55%-60% (Light Drought, LD) of maximum field water capacity, i.e., mild drought, 40%-45% (Moderate Drought, MD) of maximum field water capacity, i.e., moderate drought and 30%-35% (Severe Drought, SD) of maximum field water capacity, i.e., severe drought. On the 40th day of drought treatment, 13 indices, including seedling growth morphology, physiology, and biochemistry, were measured. The results showed that under drought stress, the height and ground diameter of P. edulis Sims gradually decreased with increasing drought stress, and there were significant differences in seedling height and ground diameter among the treatments. Drought stress significantly inhibited the growth of seven P. edulis Sims varieties. The contents of soluble sugar (SS), soluble protein (SP), proline (Pro), and other substances in P. edulis Sims basically increased with increasing drought stress. With the aggravation of drought stress, the malondialdehyde (MDA) content of P. edulis Sims tended to increase to different degrees, the superoxide dismutase (SOD) activity and peroxidase (POD) activity both tended to increase at first and then decrease, and the change in catalase (CAT) activity mostly showed a gradual increasing trend. The contents of endogenous hormones in P. edulis Sims significantly differed under different degrees of drought stress. With the aggravation of drought stress, the abscisic acid (ABA) content of P. edulis Sims tended to increase, whereas the contents of gibberellin (GA), indoleacetic acid (IAA), and zeatin nucleoside (ZR) exhibited a downward trend. A comprehensive evaluation of the drought resistance of seven P. edulis Sims varieties was conducted based on the principal component analysis method, and the results showed that the drought resistance decreased in the order XH-BL > XH-TWZ > TN1 > GH1 > ZJ-MT > LP-LZ > DH-JW.