Abstract: 【Objective】The relay-strip intercropping can expand planting area, increase production, and alleviate the domestic imbalance between supply and demand in soybean industry. However, soybean is suffered from shade stress by taller maize at seedling stage in relay-strip intercropping system. Under the shade stress, soybean morphogenesis and some physiological and biochemical characters changed significantly, which induced yield and quality reduction. The aims of this work were to study the shade tolerance of different genotypes, and provide the simple, effective, and suitable evaluation indicators of shade tolerance, and identify shade tolerance at seedling stage, and provide fine basic materials in soybean.【Method】After 20 days of emergence, twenty four morphological, biomass and physiological indexes correlating with shade tolerance of 19 soybean materials were determined under normal light (1 000 µmol·m^-2·s^-2) and weak light (400 µmol·m^-2·s^-2), such as plant hight (PH), stem diameter (SD), nodes of main stem (HN), hypocotyl length (HL), leaf area (LA), leaf thickness (LT), dry weight (DW), chlorophyⅡ a content (Chla), net photosynthetic rate (Pn), transpiration rate (Tr), initial fluorescence (Fo′), maximum fluorescence in light (Fm′) and so on. Shade tolerance coefficient (STC) of all indexes from both treatments were analyzed by using principal component analysis, membership function method, hierarchical cluster analysis and stepwise regression analysis. 【Result】 Compared with the control, the changing trend and range of morphological and physiological index were different. Six independent comprehensive components were obtained from 24 single indexes by principal component analysis, which reflected 87.65% information of all traits information. The contribution ratio of 6 principal component factors were 30.50%, 21.24%, 12.00%, 10.71%, 8.02% and 5.18%, respectively. The comprehensive shade tolerance values (D) were calculated from the membership function methods, and 19 soybean materials were divided into three shade tolerance types by cluster analysis, 2 materials were high shade tolerance type (class Ⅰ), 5 materials were medium shade tolerance type (class Ⅱ), and 12 materials were shade intolerance type (class Ⅲ). A mathematical evaluation model for soybean shade tolerance was established by stepwise regression equation: D=-0.301+0.419LDW+0.169Gs+0.031PH+0.255Fm(R²=0.959). The predictive values (VP) were basically consistent with the comprehensive shade tolerance value (D), which indicated that the use of the four indexes including leaf dry weight (LDW), stomatal conductance (Gs), plant height (PH) and maximum fluorescence in dark (Fm) to predict the shade tolerance in soybean at seedling stage is feasible. The LDW, Gs and PHof high shade tolerance type were intermediate among three types. The PH and STC of the four indexes in high shade tolerance type were the highest.【Conclusion】A comprehensive evaluation system established by multivariate statistics was used to identify shade tolerance at soybean seedling stage. In same condition, four indicators (LDW, Gs, PH, and Fm) can be used for rapid identification and prediction of soybean materials.

Key words: soybean, shade tolerance, membership function method, comprehensive evaluation, agronomic characters