In order to understand the reaction and adaption mechanism to water deficit in winter wheat (Triticum aestivum L.) planted in North China Plain, six cultivars (Bima 1 released in the 1950s, Jinan 2 released in the 1960s, Taishan 1 released in the 1970s, Jimai 26 released in the 1980s, Jimai 38 released in the 1990s, and Jimai 22 released in the 2000s) were grown under both irrigated and rain-fed conditions in two successive growing seasons from 2010 to 2012. The photosynthetic characteristics of flag leaf after anthesis and grain yields were compared under two water conditions. The yield of Jimai 22 was significantly higher than that of other cultivars. The increase of yield was along with the significant improvements of photosynthetic rate (Pn) and stomatal conductance (Gs). Under irrigated condition, Jimai 22 showed increases of 54.4%, 39.4%, 23.4%, 18.9%, and 4.2% in yield, 30.0%, 15.9%, 15.2%, 9.8%, and 5.5% in Pn, and 46.1%, 35.9%, 23.1%, 7.3%, and 6.6% in Gs compared with the previous cultivars Bima 1, Jinan 2, Taishan 1, Jimai 26, and Jimai 38, respectively. Under rain-fed condition, Jimai 22 showed increases of 46.0%, 37.6%, 21.5%, 18.8%, and 3.2% in yield, 41.5%, 29.1%, 19.8%, 11.2%, and 6.7% in Pn, and 68.4%, 48.7%, 30.6%, 10.7%, and 10.6% in Gs compared with the previous cultivars, respectively. Under rain-fed condition, the Pn and Gs of all cultivars were lower than those under irrigated condition, and these of Jimai 22 showed the least reduction, indicating that Jimai 22 has higher photosynthetic adaptation to water deficiency. However, compared with the irrigated treatment, the rain-fed treatment showed 6.6–11.7% of yield decrease in different cultivars, with the largest reduction percentage in Jimai 22. Therefore, we concluded that the current wheat cultivars in North China Plain have high-yield potential under water-sufficient condition, but they are sensitive to water deficiency, with a relatively strong photosynthetic adaptation to water deficiency.
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