| Four buckwheat cultivars with different lodging resistance were used in the field experiment during the 2012～2013 to study the relationship between lodging resistance and mechanical properties, morphological characteristics, anatomical structure and lignin metabolism of culm in buckwheat. Besides, buckwheat cultivar with middle lodging resistance (NQ) was used to discuss the effects of nitrogen fertilizer and planting density on lodging resistance, mechanical properties, morphological characteristics, anatomical structure and lignin metabolism of culm, as well as the yield and yield components of buckwheat by split plot experiment design of two factors with three levels. The main results were as follows:1. The snapping resistance parameter of culm and lodging index varied significantly among buckwheat cultivars with different lodging resistance. Buckwheat cultivar with high lodging resistance (XD), had high snapping resistance parameter of culm, low lodging index and lodging percentage. Correlation analysis showed that the lodging percentage was very significantly negatively correlated with snapping resistance parameter of culm (r=-0.907, P< 0.01), and very significantly positively correlated with lodging index (r= 0.842, P< 0.01). Thus, the snapping resistance parameter of culm and lodging index can be used as important indicator to evaluate lodging resistance of buckwheat.2. The lodging resistance of culm in buckwheat was closely related to the morphological characteristics, anatomical structure and lignin metabolism. Compared with buckwheat cultivar with middle lodging resistance (NQ and XN) and buckwheat cultivar with low lodging resistance (WK), the plant height, gravity center height, H/D, diameter of 2nd internode, mechanical tissue layer number, mechanical tissue thickness, culm wall thickness, large vascular bundle number, vascular bundle area, lignin content and activities of PAL, TAL,4CL, and CAD of buckwheat cultivar with high lodging resistance (XD) significantly increased, while the length of 2nd internode and small vascular bundle number significantly decreased. Correlation analysis showed that the lodging percentage was very significantly negatively correlated with H/D, diameter of 2nd internode, mechanical tissue thickness, culm wall thickness, vascular bundle area, lignin content and activities of PAL,4CL, and CAD (r=-0.955, -0.866, -0.881, -0.947, -0.846, -0.844, -0.872,-0.838, -0.870, P< 0.01), and significantly negatively correlated with large vascular bundle number and mechanical tissue layer number (r=-0.709, -0.806, P< 0.05), and significantly positively correlated with length of 2nd internode (r= 0.820, P< 0.05), but not with plant height, gravity center height, small vascular bundle number and TAL activity (r=-0.595, -0.612,0.529, -0.453, P> 0.05). The lignin content was very significantly positively with activities of PAL,4CL, and CAD (r= 0.984,0.927, 0.862, P< 0.01), but not with TAL activity (r= 0.619, P> 0.05). The MLR analysis between lignin content and activities of PAL, TAL,4CL and CAD showed that the PAL and 4CL were the key enzymes that influenced the lignin content of the 2nd internode. The results indicated that the buckwheat cultivars with high resistance to culm snapping and lodging usually have short and thick 2nd internode, and more mechanical tissue layer number and large vascular bundle number, and large H/D, mechanical tissue thickness, culm wall thickness and vascular bundle area, and high lignin content and activities of PAL,4CL, and CAD.3. Nitrogen fertilizer and planting density significantly influenced the culm characteristics of buckwheat. With the increase of nitrogen fertilizer, the snapping resistance parameter of culm, diameter of 2nd internode, mechanical tissue layer number, mechanical tissue thickness, culm wall thickness, large vascular bundle number, and vascular bundle area increased and then decreased, and the lodging index, plant height, gravity center height, and length of 2nd internode increased, and the H/D, lignin content, and activities of PAL, TAL,4CL and CAD decreased, while the small vascular bundle number had not much changed. Besides, with the increase of planting density, the lodging index, plant height, gravity center height, and length of 2nd internode increased, and the snapping resistance parameter of culm, H/D, diameter of 2nd internode, mechanical tissue layer number, mechanical tissue thickness, culm wall thickness, large vascular bundle number, vascular bundle area, lignin content, and activities of PAL, TAL,4CL and CAD decreased, while the small vascular bundle number had not much changed. The results indicated that the increase of nitrogen fertilizer and planting density result in culm quality deterioration of buckwheat, and lead to the low lodging resistance of buckwheat.4. Nitrogen fertilizer and planting density had very significantly effects on yield and yield components of buckwheat. With the increase of nitrogen fertilizer and planting density, the yield, primary stalk pitch number, branch number, grain number per plant, grain weight per plant, and 1000-grain weight increased and then decreased, and the maximums of them were appeared in nitrogen fertilizer of 45 kg/ha, and planting density of 9 105 plants/ha.From the results we concluded that, the lodging resistance of culm in buckwheat was closely related to the culm characteristics of buckwheat, the snapping resistance parameter of culm and lodging index can be used as important indicator to evaluate lodging resistance of buckwheat. The buckwheat cultivars with high resistance to culm snapping and lodging usually have short and thick 2nd internode, more mechanics tissue layer number and large vascular bundle number, and large H/D, mechanical tissue thickness, culm wall thickness and vascular bundle area, and high lignin content and activities of PAL,4CL and CAD. Besides, the nitrogen fertilizer of 45 kg/ha and planting density of 9 105 plants/ha, which can reduce the competitions of buckwheat plants among groups, and help the growth of plants, and effectively optimize the structures and compositions of cum in buckwheat, and improve the culm quality, and reduce the risk of lodging, and finally increase the yield of buckwheat. |
