[Shade-tolerance indices of maize: selection and evaluation]

A field experiment was conducted to study the morphological, physiological, and yield traits of 24 maize cultivars under 50% shading. Comparing with the control, 50% shading decreased the plant height, stem diameter, leaf net photosynthetic rate (Pn), specific leaf weight (SLW), aboveground dry matter accumulation, ear length and diameter, axis diameter, and kernels per row. The interval from anthesis to silking (ASI) was prolonged, and the grain yield was decreased significantly. The percent changes of ASI, Pn, SLW, and kernels per row were significantly correlated with aboveground dry matter accumulation and grain yield, being able to be used as the indices to evaluate the maize shade-tolerance in field. Cluster analysis using comprehensive shade-tolerance traits as evaluation parameters indicated that 14 maize cultivars including Zhengdan 958, Xundan 20, and Denghai 602, etc. were of shade-tolerance type, and 10 cultivars (Anyu 12 and Yuyu 22, etc. ) were of shade-sensitive type. It was suggested that adopting the morphological, physiological and yield traits as the indices to evaluate the shade-tolerance of maize would be more objective, simple and practical.