Effects of uniconazole on the lignin metabolism and lodging resistance of culm in common buckwheat (Fagopyrum esculentum M.)

Lodging is one of the major factors contributing to common buckwheat (Fagopyrum esculentum M.) yield and quality reduction. This study was conducted to determine whether lignin metabolism and lodging resistance of culm in common buckwheat could be affected by uniconzole. Two common buckwheat cultivars, Youqiao2 (lodging-tolerant cultivar; YQ2) and Ukraine daliqiao (lodging-susceptible cultivar; UD), were used to investigate the effects of uniconzole on the common buckwheat lodging behavior, lignin metabolism in culm and its relation to lodging resistance. In one experiment, seed dressing with uniconazole at the rate of 0 (CK1), 100 (P1), 200 (P2), and 300 (P3) mg kg−1 were applied. In the second experiment, foliar spraying with uniconazole at the rate of 0 (CK2), 25 (S1), 50 (S2), 75 (S3), and 100 (S4) mg L−1 were applied at the four-leaf stage. Results showed that the lignin content was significantly and positively correlated with culm snapping resistance, while significantly and negatively correlated with lodging index and lodging percentage. The lodging index and lodging percentage decreased and then increased with the increase of the concentration of uniconazole, and their minimum values appeared in the P2 and S3 treatments. The yield, culm snapping resistance, lignin content, and the enzyme activities of phenylalanine ammonia-lyase (PAL), 4-coumarate:CoA ligase (4CL), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD) increased and then decreased with the increase of the concentration of uniconazole, and their maximum values appeared in the P2 and S3 treatments. These results suggested that the lignin content is closely related to the lodging resistance of common buckwheat, and higher lignin content could strengthen the lodging resistance of common buckwheat. Uniconazole significantly decreased the risk of lodging occurred by increasing the lignin content and its related enzymes activities of culm, and the concentrations which showed the greatest effects were 200 mg kg−1 with seed dressing and 75 mg L−1 with foliar spraying.