Effects and Allelopathy of Leek-cucumber Crop Rotation in Controlling Cucumber Blight

Purpose To investigate the control effects of cucumber-leek crop rotation on cucumber blight, and the effect of different tissue volatiles and extracts of leek on cucumber seed germination and the inhibitory activity of Phytophthora melonis.

Methods The leeks and cucumbers were rotated, and the cucumbers were inoculated with P. melonis in the first crop. According to the incidence rate, the control effect of crop rotation mode on cucumber blight was analyzed. Broad-leaf leek and narrow-leaf leek were used as experimental materials. The germination of cucumber seeds were counted under the influence of different weights of volatiles from stems and leaves and different mass concentrations of extracts, and the allelopathic substances from different tissues of leek on cucumber seed germination were analyzed. Antibacterial tests of different weights of leek volatiles and different mass concentrations of extracts on the mycelium of P. melonis were conducted, and the effects of allelopathic substances from different tissues of leek on the germination of P. melonis mycelium, spores rest, and germination of resting spores were analyzed.

Results The utilization of leek and cucumber crop rotation could effectively control the occurrence of cucumber blight caused by continuous cropping, and the inhibition rate was 24.37%. The Logistic curve based on the incidence rate fitting showed that leek and cucumber crop rotation could reduce the maximum instantaneous growth rate of the incidence rate of cucumber blight. Both volatiles and extracts of leek were able to effectively inhibit the mycelial growth of P. melonis, and also interfere with the free-swimming spores and resting spore germination of P. melonis, in which, the extracts of leek stems were more effective than the leaves. In addition, leek volatiles were also able to promote cucumber seed germination at low weight.

Conclusion The leek and cucumber crop rotation pattern can interfere with the infection process of P. melonis through allelopathy, effectively inhibiting the occurrence spread of the disease.