Over the last few years there has been an increase in short-cycle maize harvesting. On the one hand precocious maize has allowed for the broadening of the cultivated area to marginal regions, while semiprecocious types have shown operative and commercial advantages when compared with normal cycle hybrids in typical traditional areas of the Argentine maize belt. Within the breeding plan to obtain precocious materials, which has been under development since 1988, the differential behavior of testers and lines has been determined through the evaluation of their hybrid combinations, revealing crosses (lines x tester) which stood out against the rest, as regards precocity and yield. Two short-cycle materials with flint grain were used as pollinators, tester 1 (t1) and 2 (t2). Tester t2 is Gaspé variety with extreme precocity and t1 is a selected inbred line. They were crossed with seven different lines: B73 and A632 (USA), P465, P1338 and H38 (EEA INTA, Pergamino), AFE and AW (IFSC, UNLP). During the 1993-94 and 1994-95 campaign (F1´s) hybrids were evaluated using a randomized complete-block design with 3 replications. The traits considered were: EL- Ear length, in cm, NKR- Number of kernels per row, NRE- Number of rows per ear, KY- Kernel yield per plot (kg ha-1), HUT- Heat units to tasseling in ?C. A variance analysis was carried out using a hierarchical factorial pattern, Table 1. The difference between tester and lines estimates the general combining ability (GCA) directly. It was estimated as follows: l_i = x_i.- x_.. and l_j = x_.j - x_..; where x_i. is Line mean, x_.j is Tester mean, and x_.. is Grand mean. The interaction tester x line determined the specific combining ability (SCA). A multiple comparisons test, using least significant differences (LSD, 5%), allowed a test of the significance of the individual GCA and SCA (Tables 2, 3, 4).

It was concluded that for HUT, the lines B73 and A632 were those that offered the highest number of alleles for early flowering, the lines P1338 and H38 were significantly different from the rest for EL, and the B73 line offered the highest NRE. Given that the error means square for tester x line interaction depends on the effects of dominance, these would be non-existent for most of the evaluated traits, with the exception of EL. P1338 x t1 and H38 x t1 were the combinations that significantly surpassed the rest (Table 4). It was shown that the behavior of the hybrids may be adequately explained by the GCA, which depends exclusively on the additive and possibly epistatic effects. This would guarantee advancement in selection, in cases where some hybrids may participate in the formation of a synthetic population.

Tester t1 proved to be the one which offers higher grain yield per plot compared with its hybrid combinations. Nevertheless, when considering HUT, this does not show any difference from t2 (of extreme precocity)(Table 1). In conclusion, it has been shown that t1 is the most adequate for use in breeding plans for precocity and grain.

Table 1. F values for each of the traits: EL, NKR, NRE, KY and HUT.
 

S. of Variation	GL	EL	NKR	NRE	KY	HUT
Tester	1	2.61NS	0.03NS	9.52NS	145,000* *	17.64NS
Line	6	5.11*	2.10NS	11.53**	0.61NS	7.68*
Tester X Year	1	6.16*	23.10**	7.16**	0.00NS	1.48NS
Line X Year	6	1.48NS	3.50**	1.09NS	1.73NS	2.16NS
Tester X Line	6	4.46*	1.28NS	1.98NS	1.09NS	2.08NS
Linextesterxyear	6	0.59NS	1.27NS	1.34NS	1.47NS	1.17NS
Error	54

*, ** : Significant at 1 and 5 % respectively. NS : Not significant.

Table 2. Means, LSD 5%. and GCA for lines (l_i).
 

	Lines	Means	LSD: 0.62	li
NRE	B73	13.86	a	0.935
	P465	13.29	a b	0.365
	AFE	13.16	b c	0.235
	P1338	12.96	b c	0.035
	AW	12.65	b c	-0.275
	A632	12.60	c d	-0.325
	H38	11.93	d	-0.995
	Lines	Means	LSD: 1.11	li
EL	P1338	20.03	a	1.615
	H38	20.02	a	1.605
	A632	18.40	b	-0.015
	B73	17.87	b c	-0.545
	AW	17.82	b c	-0.595
	P465	17.53	b c	-0.885
	AFE	17.23	c	-1.185
	Lines	Means	LSD: 44.7	li
HUT	AFE	1,197	a	70
	AW	1,167	a b	40
	P1338	1,140	b c	13
	P465	1,135	b c	8
	H38	1,117	c	-10
	B73	1,067	d	-60
	A632	1,066	d	-61

Table 3. Means, LSD 5%, and GCA for the Tester (l_j)
 

	Tester	Means	LSD:0.71	lj
KY	t1	2.46	a	0.23
	t2	1.99	b	-0.23

Table 4. Means, LSD 5% and GCA for the hybrids.
 

	Hybrid	Means	LSD: 1.08
EL	H38 x t1	21.84	a
	P1338 x t1	21.09	a
	P1338 x t2	18.97	b
	A632 x t1	18.07	b c
	P465 x t1	18.56	b c
	H38 x t2	18.19	b c
	A632 x t2	18.13	b c
	AW x t1	17.93	b c
	B73 x t1	17.92	b c
	B73 x t2	17.82	c
	AW x t2	17.71	c
	AFE x t1	17.35	c d
	AFE x t2	17.12	c d
	P465 x t2	16.49	d

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