BREEDING IMPLICATION OF INTRA- AND INTERHETEROTIC GROUP CROSSES AS SOURCE OF NEW INBRED LINES IN MAIZE

Voichita Has, Ioan Has

Agricultural Research Station, Turda; CP 401100, Turda,

Agriculturii, 27 Street, Jud. Cluj;

Tel. +40-0264-311680; Fax +40-0264-311792;

E-mail: hasvoichita@yahoo.com

Advanced cycle pedigree breeding is the most common method for developing maize inbreds. Many of the current elite maize inbreds are derived from only a few progenitor inbreds; this breeding process systematically leads to a narrow maize germplasm within heterotic groups. Maize breeders have sometimes used commercial hybrids as a source of new inbreds. The effects of disrupting heterotic patterns in maize, by selfing from commercial hybrids, are not well understood.

The objective of this study was to compare intra- and interheterotic group crosses as sources of new inbred lines. We evaluated 425 inbred lines, created at Agricultural Research Station – Turda, Romania. The inbred lines have been derived from different sources of germplasm using conventional breeding techniques of pedigree selection and early-generation yield testing. We used in inbred lines development the following sources of germplasm: local varieties 3%, composites 14%, improved elite inbred lines 47% and commercial hybrids 36%.

Twelve of these inbred lines were selected by the year when they were finalized (Table 1). The inbred lines have been crossed with two testers - inbred lines, belonging to flint heterotic pattern. The testcrosses were evaluated in randomised complete block design in two locations for 2 years. Analysis of variance was performed for grain yield, stalk and root lodging, kernel dry matter and selection index. (Table 2).

The new elite inbred lines were crossed with more testers (7-8 inbred lines per year) from different heterotic patterns. They were evaluated (Table 3) by their GCA for the main characters.

The testcross means classified the inbred lines in, good for:

- grain yield: TC 385A, TA 428, TE 203, TD 268, TC 365, TC 344, TD 345;

- stalk and root lodging resistance: TD 273, TD 268, TC 335, TC 365, TC 344;

- kernel dry matter: TD 273, TC 335, TE 210, TC 344, TD 345, TD 348;

- selection index: TA 428, TD 268, TC 365, TC 344, TD 345.

In conclusion:

1) Last years were characterized by a genetic gain in inbred lines development.

2) GCA effects for the main characters were more favourable for inbred lines derived from improved elite inbreds and commercial hybrids.

3) The local populations would be used as sources of inbred lines only after they were improved in a special program by recurrent or reciprocal-recurrent selection.

4) The relative usefulness of intra- versus intergroup populations as sources of new inbreds depends on the particular inbreds used and/or on finding a suitable tester.

Table 1. « Turda » inbred lines are listed by four decades of important use

Inbred line	Decade of impotant use	Year of finalized	Source of germoplasm *		Origin of initial material
Maternal inbreds « m »
1. T 248	1961 – 1970	1964	LCS		Commercial hybrid – KS 3
2. T 291		1966	RYD		Local variety – Ungheni 247
3. T 243		1965	RYD		Commercial variety– VIR 42
4. T 169a	1971 – 1980	1972	RYD x ?		(W153R x W37A) xMihalţ 256
5. T 158		1971	RYD x ?		(W153R x W37A) x Mihalt 1745
6. T 160		1971	RYD		Commercial hybrid – KC 3VI
7. TC 243	1981 – 1990	1989	WF 9 Group x RYD		Commercial hybrid
8. TB 366		1987	LSC		W182B x T 248-I
9. TC 316		1988	? x LCS		S 54 x MO 17
10. TC 344	1991 – 2000	1995	RYD		Commercial hybrid
11. TC 335		1994	(LSC x RYD) x ID		(T 248 x T 291) x TB 329
12. TE 203		1996	RYD		TD 261^2 x T 291
Paternal inbreds « n »
LO 3	-		ELF	Pop de Lostrano
PI 187	-		ELF	PTF x Pop Italia

RYD - Reid Yellow Dent; LSC - Lancaster Sure Crop ID - Iodent ; ELF - European Late Flint

Table 2. Additive genetic effects (ĝm) for m=12 inbred lines, n=3;

- a factorial crossing systems “m x n” (12 x 3) x 2 locations x 2 years -

Trait	Grain yield	Dry matter of grain at harvest	Percent of plants not stalk lodging at harvest	Selection Index
Inbred lines « m » *
1. T 248^3	- 0.61	- 0.07	6.77	6.09
2. T 291^1	2.17	- 0.34	4.62	6.45
3. T 243^3	- 1.84	- 0.84	- 6,29	- 8.97
-created in ‘1960	- 0.28	- 1.25	5.10	3.57
4. T 169a^2	- 11.55	2.00	4.88	- 4.67
5. T 158^3	1.33	0.17	- 9.14	- 7.64
6. T 160^3	- 12.98	0.59	2.13	- 10.26
- created in ‘1970	- 23.20	2.76	- 2.13	- 22.57
7. TC 243^3	8.26	- 1.04	- 2.06	5.16
8. TB 366^2	- 3.07	1.09	- 4.78	- 6.76
9. TC 316^2	- 0.87	- 2.10	0.56	- 2.41
- created in ‘1980	4.32	- 2.05	- 6.28	- 4.01
10. TC 344^3	7.52	- 0.58	- 0.92	6.02
11. TC 335^2	4.97	0.79	2.80	8.56
12. TE 203^2	6.67	0.36	1.45	8.48
- created in ‘1990	19.16	0.57	3.33	23.06
DL 5%	3.14	0.40	3.47	-

* Inbred lines were derived from: ¹= open-pollinated varieties; ² = improved elite inbred lines; ³ = commercial hybrids.

Table 3 General combining ability (GCA) specific to 11 new “TURDA” inbred lines in maize

Inbred line	Year of testing	No. crosses	Grain yield (DMG = 15,5%)		Percent of plants not stalk lodged at harvest		Dry matter of grain at harvest		Selection index % *
			q/ha	% *	%	% *	%	% *
Source: BK of elite inbred lines
1. TC 385 A	1999	41	101.3	98	92.0	99	72.0	103	100
	2001	27	114.6	98	91.2	99	81.3	99	95
	2002	35	113.1	109	91.6	95	80.2	99	102
GCA/ TC 385A			108.8	99	91.9	98	76.2	101	99
2. TA 428	1999	66	103.5	100	92.0	99	71.9	103	102
	2001	3	127.3