Table 1. Effects of polyamine on the yield and yield components of winter wheat.

Year	Cultivar	Treatment	Spike number (×104 hm−2)	Grain number per spike	1000-grain weight (g)	Grain yield (t hm−2)
2011–2012	Zhoumai 18	Spd	415.1 a	33.4 a	51.6 a	7.3 a
		Spm	414.3 a	33.5 a	51.3 a	7.3 a
		Put	414.9 a	33.1 a	48.9 b	6.7 b
		CK	415.0 a	32.8 a	49.6 b	6.8 b
	Xinong 538	Spd	452.3 a	33.9 a	41.9 a	6.7 a
		Spm	450.9 a	34.3 a	42.3 a	6.7 a
		Put	451.8 a	33.5 a	39.5 b	6.0 b
		CK	451.8 a	33.7 a	40.1 b	6.1 b
2012–2013	Zhoumai 18	Spd	406.8 a	34.5 a	52.1 a	7.3 a
		Spm	407.7 a	34.4 a	52.2 a	7.4 a
		Put	405.3 a	34.2 a	49.3 b	6.8 b
		CK	405.9 a	33.9 a	49.7 b	6.8 b
	Xinong 538	Spd	443.6 a	32.8 a	42.5 a	6.2 a
		Spm	442.4 a	33.4 a	42.6 a	6.3 a
		Put	441.8 a	32.4 a	39.5 b	5.7 b
		CK	442.3 a	32.5 a	39.8 b	5.7 b

Values within a column for the same cultivar and the same year followed by different letters are significantly different at P = 0.05. S1: external Spd application on panicles; S2: external application of Spm on panicles; P1: external application of Put on panicles.