Maize Genetics Cooperation Newsletter vol 81 2007

Breeding implication of intra- and interheterotic group crosses as a source of new inbred lines in maize

--Has, V; Has, I

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 the Agricultural Research Station in 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 the following sources of germplasm for inbred line development: 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 a 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 showed good results for grain yield: TC385A, TA428, TE203, TD268, TC365, TC344, TD345; stalk and root lodging resistance: TD273, TD268, TC335, TC365, TC344; kernel dry matter: TD273, TC335, TE210, TC344, TD345, TD348; selection index: TA428, TD268, TC365, TC344, TD345.

In conclusion:

1) The 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.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of authors.

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

Inbred line	Decade of important use	Year finalized	Source of germplasm*	Origin of initial material
Maternal inbreds (m)
T248	1961 – 1970	1964	LCS	Commercial hybrid KS3
T291		1966	RYD	Local variety Ungheni 247
T243		1965	RYD	Commercial variety VIR42
T169a	1971 – 1980	1972	RYD x ?	(W153R x W37A) x Mihalţ256
T158		1971	RYD x ?	(W153R x W37A) x Mihalt 1745
T160		1971	RYD	Commercial hybrid KC3VI
TC243	1981 – 1990	1989	WF9 Group x RYD	Commercial hybrid
TB366		1987	LSC	W182B x T248-I
TC316		1988	? x LCS	S54 x MO17
TC344	1991 – 2000	1995	RYD	Commercial hybrid
TC335		1994	(LSC x RYD) x ID	(T248 x T291) x TB329
TE203		1996	RYD	TD261^2 x T291
Paternal inbreds (n)
LO3	-		ELF	Pop de Lostrano
PI187	-		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 system 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)*
T248^3	- 0.61	- 0.07	6.77	6.09
T291^1	2.17	- 0.34	4.62	6.45
T243^3	- 1.84	- 0.84	- 6.29	- 8.97
-created in �1960	- 0.28	- 1.25	5.10	3.57
T169a^2	- 11.55	2.00	4.88	- 4.67
T158^3	1.33	0.17	- 9.14	- 7.64
T160^3	- 12.98	0.59	2.13	- 10.26
-created in �1970	- 23.20	2.76	- 2.13	- 22.57
TC243^3	8.26	- 1.04	- 2.06	5.16
TB366^2	- 3.07	1.09	- 4.78	- 6.76
TC316^2	- 0.87	- 2.10	0.56	- 2.41
-created in �1980	4.32	- 2.05	- 6.28	- 4.01
TC344^3	7.52	- 0.58	- 0.92	6.02
TC335^2	4.97	0.79	2.80	8.56
TE203^2	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: ¹open-pollinated varieties; ²improved elite inbred lines; ³commercial 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
TC385 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/ TC385A			108.8	99	91.9		98		76.2		101		99
TA428	1999	66	103.5	100	92.0		99		71.9		103		102
	2001	3	127.3	108	82.0		89		81.1		98		95
	2002	67	110.9	106	95.0		99		79.7		98		104
GCA/ TA428			107.7	103	93.3		99		75.9		100		103
TE203	1999	35	98.7	95	92.5		100		76.6		109		104
	2001	85	115.1	98	88.5		96		82.5		100		94
	2002	100	100.9	97	94.3		97		81.9		101		95
GCA/ TE203			106.0	97	91.8		97		81.3		102		96
TD273	1999	13	110.2	97	91.1		98		70.6		101		96
	2001	23	110.5	94	96.3		100		82.6		100		99
	2003	77	81.2	97	98.6		100		84.6		100		98
GCA/ TD273			90.5	96	97.3		100		82.6		100		98
TD268	2001	91	115.2	98	97.1		106		80.8		98		102
	2003	61	86.5	103	96.5		98		82.9		98		100
GCA/ TD268			103.4	100	96.9		103		81.6		98		101
TC335	1999	21	94.9	92	94.0		102		73.3		105		97
	2001	34	108.4	92	93.6		102		82.4		100		94
	2003	29	85.1	102	96.4		98		84.1		100		99
GCA/ TC335			97.0	95	94.7		101		80.7		101		96
TC365	1999	38	109.3	106	93.5		101		70.7		101		108
	2001	22	125.2	107	97.7		106		81.5		99		112
	2002	40	109.5	105	95.7		99		80.2		99		103
	2003	38	88.9	106	95.8		98		84.5		100		106
GCA/ TC365			106.3	106	95.4		100		79.0		100		107
Comparison mean: Saturn, Helga (commercial hybrids)	1999	50	103.5	100	92.5		100		70.1		100		100
	2001	50	117.4		92.0				82.4
	2002	50	104.2		96.5				80.9
	2003	50	83.8		98.2				84.4
Source : commercial hybrids
TE210	1999	29	102.6	99	92.5		100		72.9		104		103
	2001	44	111.5	95	89.5		97		83.5		101		94
	2003	73	86.1	103	92.2		94		85.9		102		98
GCA/ TE210			97.0	100	91.4		96		82.6		102		98
TC344	1999	70	104.0	100	94.0		102		72.8		104		106
	2001	125	119.9	103	92.4		101		82.1		100		102
	2002	112	111.6	107	96.6		100		80.4		99		107
	2003	55	90.8	108	94.4		96		84.5		100		104
GCA/ TC344			109.8	104	94.3		100		80.1		100		105
TD345	1999	34	102.7	99	91.5		98		74.3		106		103
	2001	28	112.7	96	92.0		100		83.1		101		97
	2002	56	107.7	103	95.0		98		82.0		101		103
	2003	37	85.3	102	91.8		93		85.0		101		96
GCA/ TD345			102.2	101	92.9		97		81.2		102		100
TD348	1999	10	102.1	99	95		103		70.2		100		101
	2002	55	101.3	97	96.7		100		81.9		101		99
	2003	60	84.6	101	93.1		95		84.1		100		95
GCA/ TD348			93.3	99	94.8		98		82.0		100		97
Comparison mean: Saturn, Helga (commercial hybrids)	1999	50	103.5	100	92.5		100		70.1		100		100
	2001	50	117.4		92.0				82.4
	2002	50	104.2		96.5				80.9
	2003	50	83.8		98.2				84.4

*GCA of the Turda inbred lines has been compared with the mean of the two hybrids.