Abstract: A field experiment was conducted to study the differences of main agronomic traits, yield and SPAD value of 36 wheat (Triticum aestivum L.) varieties (lines) from Southwest Wheat Region under two nitrogen levels of no nitrogen application (N0) and normal nitrogen application (N1, pure nitrogen application rate of 135 kg/hm²) , in order to provide reference for nitrogen-efficient wheat breeding. Based on the grain yield, the varieties (lines) were divided into three types: high yield type, middle yield type and low yield type. The average yield of high yield type was 7 334.60 kg/hm², which was 1.70 times that of low yield type and 1.27 times that of the middle yield type. Based on yield differences under two nitrogen application levels, the wheat varieties (lines) were classified into four categories: dual-efficient type, low-N-efficient type, high-N-efficient type, and dual-inefficient type. Among them, 10 varieties (lines) were dual-efficient type, 6 varieties(lines) were high-N-efficient type, 7 varieties(lines) were low-N-efficient type, and 13 varieties(lines) were dual-inefficient type. The average yield showed significant differences among the four nitrogen efficiency types, following the order of dual-efficient type, high-N-efficient type, low-N-efficient type and dual-inefficient type from high to low. However, no significant differences were observed in spikelet number, leaf length, spike length, and plant height among these four types. Yunmai 83, Yunmai 80, Chuanmai 1648, Yunmai 56, Chuanmai 84, and Yunmai 68 were not only dual-N-efficiency varieties (lines), but also high yield varieties (lines). Consequently, these varieties could serve as nitrogen-efficient wheat germplasm resources for breeding applications.

Key words: wheat(Triticum aestivum L.), nitrogen efficiency type, yield, agronomic characters, Southwest Wheat Region