During the period from 1985 winter to 1993 autumn, two normal sweet corn lines (Yitain No. 83 and Yitain No. 33) and one super sweet corn line (Yitain dwarf No. 1) were developed. These lines have been tested and used in hybrid production as new germplasm resources. Three lines are maintained by and are available from the Institute of Genetics, Academia Sinica.

(1) Yitain No. 83 and Yitain No. 33: These lines were developed by continued inbreeding and selection from the sweet corn varieties A and B. They impart high general and specific combining ability. Yield of young ears of the cross combination Yitain No. 83 x Yitain No. 33 and Yitain No. 83 x Yitain No. 185 (baby corn) were high and stable, and were 24.0% and 35.9% higher than the control, normal sweet corn No. 8701 (ck), respectively. The two lines are also fairly resistant to Helminthosporium turcicum, H. maydis, Fusarium graminearum, and Diplodia maydis and D. macrospora. The degree of resistance to H. turcicum is 1, indicating polygenes or horizontal resistance. They are mid-late in maturity, mid-tall in plant and ear height. Stalks are fair, roots are vigorous, leaves are semi-erect and mid-sized. They usually have two or three cylindrical young ears per plant and produce yellow kernels on white cobs.

(2) Yitain dwarf No. 1: We bred this line by using continued inbreeding and dwarf selection from improvement population I sh2 which was bred by recurrent selection. Yitain dwarf No. 1 has good general and specific combining ability. The yield of the cross combination Yitain dwarf No. 1 x Yitain No. 20m is high, and is higher than the control (ck).

Yitain dwarf No. 1 showed a wide spectrum of resistance and ideal plant morphology. The degree of resistance is 1, which indicates polygenes or horizontal resistance. It is medium in maturity and medium in plant and ear height. Stalk and root qualities are good. The percentage of double ears per plant is high.

The lines have different responses to different types of cms (Table 1).

Table 1. Fertile reaction of three lines to different cms types.
 

	Cytoplasm
Line	T	S	C
Yitain No. 83	-	-	+
Yitain No. 33	-	+	-
Yitain dwarf No. 1	-	-	-

Notes: +, full restoration; -, full maintenance.

To sum up, three inbred lines were developed by different methods from various sweet corn materials. Though each possessed its own characters and specific properties, all showed good disease resistance, superior agronomic characters and high combining ability. The lines have different responses to different types of cms. The breeding of the three inbred lines has enriched the maize germplasm in our country. 

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