Characteristics Of Stem Lodging Resistance Of Relay Strip Intercropping Soybean And Its Relationship With Lignin Synthesis At Seedling Stage

Lodging is an important factor that restricts soybean yield and quality in maize-soybean relay strip intercropping pattern. This study was based on the special phenomenon that soybean lodging at seedling stage concurrent with stem vines. The purpose of this study was to screen the suitable comprehensive index to evaluate the lodging resistance ability of relay strip intercropping soybean at seedling stage, as well as to analysis the relationship of soybean resistance ability and stem vine. In this study, we research the stem morphological characteristics, mechanical characteristics, anatomical structural characteristics and lignin content and related lignin synthase activity systematically, then analysis the different formation process of different shade tolerant soybean varieties with different lodging resistance ability, and discuss the effect of different shade degree on the lodging resistance ability. The main results are as follows:1. The comprehensive evaluation system with four lodging resistance index including plant main stem length, stem diameter, stem flexural strength and aboveground biomass were confirmed through identification and screening experiment [(snapping resistance × stem diameter)/(above-ground biomass xmain stem length)]. It is confirmed that the lodging resistance index after sowing for 35 days showed significant negatively correlation with actual lodging percentage, which can accurately reflect the difference of lodging resistance of relay strip intercropping soybean at seedling stage and it is suitable for the evaluation of lodging resistance of relay strip intercropping soybean.2. The stem morphology influence lodging resistance ability greatly. In maize-soybean relay strip intercropping system, the main stem length increased significantly while the stem diameter and aboveground biomass reduced significantly. Soybean cultivars with strong lodging resistance ability changes little under shade conditions. Correlation analysis showed that the actual lodging percentage was significantly positively correlated with main stem length and significantly negatively correlated with stem diameter; meanwhile, the actual lodging percentage was significantly positively correlated with the weighted vining index of stem(r=0.460). In intercropping soybean production, short stem length, thick stem diameter, less degree of stem vine are the concrete manifestation of strong lodging resistance ability.3. The mechanical characteristics influence lodging resistance ability greatly. Relay strip intercropping reduced the stem snapping resistance and lodging resistance index significantly. Correlation analysis showed that the actual lodging percentage was significantly negatively correlated with stem snapping resistance, lodging resistance. Soybean cultivars with strong shade tolerant ability showed bigger stem napping resistance and higher lodging resistance index, exhibiting stronger lodging resistance ability and lower actual lodging percentage.4. The anatomical structure characteristics influence lodging resistance ability greatly. Relay strip intercropping reduced the cross sectional area of the stem, pith area, xylem area, the ratio of xylem in cross-section significantly, increased the ratio of pith in cross-section significantly. Correlation analysis showed that actual lodging percentage was significantly negatively correlated with the cross sectional area of the stem, pith area, xylem area, ratio of xylem in cross-section, significantly positively correlated with the ratio of pith in cross-section. Larger xylem area and the ratio of xylem in cross-section, smaller ratio of pith in cross-section are the anatomical features of strong lodging resistance ability.5. The stem lignin content and related synthetic enzyme activities influence lodging resistance ability greatly. Relay strip intercropping reduced the stem lignin content and related synthetic enzyme activities. Soybean variety with strong shade tolerant ability contains more lignin and higher enzyme activities of phenylalanine aminotransferase (PAL),4-coumarate:CoA ligase (4CL), cinnamic acid dehydrogenase (CAD) and peroxide enzyme (POD). Correlation analysis showed that the lignin content was significantly negatively correlated with actual lodging rate, significantly positively correlated with flexural strength and lodging resistance index, significantly positively correlated with 4CL, CAD at seedling stage, significantly positively correlated with POD,4CL at the symbiotic 34 days. Higher stem lignin content is the physiological foundation of the improvement of lodging resistance ability, while 4CL, CAD enzymatic activity are the enzyme mechanism of lignin synthesis and difference of lodging resistance ability formation.6. Varying degrees of shade have a significant influence on soybean lodging resistance ability. The more severe the degree of shading, the longer the plant stem, the lower the stem diameter, aboveground biomass and lignin content in stems, the smaller the stem flexural strength and Stem lodging index, the weaker the plant lodging resistance ability, the higher the actual lodging percentage. Selection of appropriate maize and soybean varieties and proper wide narrow row configuration can improve the light condition of relay strip intercropping soybean the performance of lodging resistance.