Evaluation of combining ability of inbred maize lines for precocity and yield
--Aulicino, MB; Naranjo, CA

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: li = xi.- x.. and lj = x.j - x..; where xi. 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 (li).
 
 
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 (lj)
 
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


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

Return to the MNL 71 On-Line Index
Return to the Maize Genome Database Page