General combining ability of flint, waxy and dent maize early inbreds
--Corcuera, VR, Sandoval, MC, Naranjo, CA

The characterization of the foundational materials as well as their inbreeding generations through the utilization of multiple descriptors is useful and important to describe and evaluate them. Nevertheless, it is not enough to select amongst different genotypes, being necessary to submit them to field trials capable of determining the ability of yielding offspring distinguished by the high expression of their yields when they are used in hybrid combinations. This measure constitutes the general combining ability (g.c.a.) of the genotypes under study. Inbred development could be considered as a sequential process in which the worst genotypes are removed in the initial stages because of their performance or they can also be removed later based on specific combining ability tests.

During November 1996 at the Institute a 7 x 8 lattice design with 4 replicates was sown to analyze the performance of 43 single crosses between an equal number of flint, waxy and dent early inbreds developed since 1990/91 and two heterozygote testers. The crossings to obtain the F1 plants tested through this trial, were practised during the growing season 1995/96. The testers used were Z8340 and Z8543, and tests were evaluated during both seasons (1995/96 and 1996/97).

The list of participants as well as their inbreeding generation and endosperm type is shown in Table 1. The average yield for testers and each test-cross is presented in Table 2. As these values constitute a measurement of the inbreds' general combining ability (g.c.a.), all those yielding over the average of the tester used were selected. According to this, the 43 inbreds analyzed were divided into two groups, depending on the tester to which they were crossed. Inbreds showing good g.c.a. when crossed to Z 8340 are: 3011/5 (flint), 3012/6/1 (waxy), 3012/9 (waxy), 3016/7/1 (waxy), 3033 (dent), 3033/2 (dent), 3040/2 (flint), 3043/1 (flint), 3070/3 (flint), 3070/7 (flint), 3071 (flint) and 3071/3 (flint). On the other hand the inbreds denoting good g.c.a. with Z 8543 are:3008/2/1 (flint), 3008/2/4 (flint), 3011 (flint), 3012/6/2 (waxy), 3012/8 (waxy), 3016/1 (waxy) and 3040/2 (flint). This points out that 18 inbreds of the whole analyzed, show good g.c.a , yielding more than 5,700 or 6,700 Kgs kernel/Ha depending on the tester to which they were crossed.

Yields were analyzed through ANOVA-2 (Table 3). There are statistically significant differences among blocks (replicates) and treatments (participants). There is a difference of 9.86% between the average yields of blocks 1 and 3. Blocks 2 and 4 show similar average yields.

Table 1. List of participants in the g.c.a. trial.
 
No TC(A) Gn Type No  TC(B) Gn Type
4 3016/7/1 S3 waxy 1 3008/2/ S3 flint
8 3014/3/1 S2 waxy 2 3012/ S2 waxy
9 3016/7/1 S3 flint 5 3016/5/3 S4 waxy
10 3016/5/3 S4 waxy 6 3008/2/4 S3 flint
11 3043/1 LE waxy 7 3012/8 S3 waxy
14 3033/2 S3 waxy 12 3012/6/2 S3 dent
15 3016/5/3 S3 flint 13 3016/1 S2 waxy
16 3012/3 S2 waxy 17 3008/2/1 S3 waxy
18 3020/3 S3 waxy 25 3011 S2 flint
19 3016/1/0 S2 flint 31 3103 S4 flint
20 3012/6/1 S3 waxy 32 3104 S4 flint
21 3011/5 S2 flint 37 3071/1 S3 flint
22 3012/9 S3 dent 42 3071 S2 flint
24 3033/4 S3 flint 44 3070/3 S3 flint
26 3027 S2 flint 45 3033/2 S3 dent
29 3033 S2 wx/o2 46 3009 S2 dent
30 3033/3 S3 wx/o2 47 3013 S2 waxy
34 3070/7 S3 flint 49 3040/2 S2 flint
38 3071/3 S3 flint 50 3014 S2 waxy
39 3070/3 S3 flint        
40 3071/4 S3 flint 3, 23, 27, 28 y 33:plots of the tester Z8543      
43 3071 S2 flint        
48 3040/2 S2 flint        
53 3033/2 S3 dent 35, 36, 41,51 y 52: plots of the tester Z8340      

Ref.: TC(A):Test-crosses with Z 8340. TC(B): Test-crosses with Z 8543. Gn: Inbreeding generation. Type: Endosperm type of the inbred tested.

Table 2. Results of the g.c.a. trial expressed as yield in Kgs/ha.
 
Participant Average2 S.D. Variance C.V. %
1 5,358 17.29 299.10 32.28
2 5,102 7.15 51.15 14.02
4 8,404 14.10 198.84 22.00
5 5,203 9.27 86.03 17.83
6 7,400 5.43 29.52 7.34
7 9,745 9.91 98.26 10.17
8 4,678 7.90 62.40 16.89
9 4,606  5.22 27.27 11.34
10 5,151 5.84 34.17 11.35
11 8,538 10.16 103.27 11.90
12 7,366 16.14 260.50 21.91
13 7,088 7.55 56.98 10.65
14 7,014 3.20 10.27 4.57
15 4,722 6.27  3.93 13.28
16 4,891 2.22 4.93 4.54
17 7,882 7.39 54.59 9.37
18 5,547 16.17 261.45 29.15
19 5,524 7.25 52.51 13.12
20 7,111 40.09 1606.90 65.37
21 6,434 3.90 15.23 6.07
22 5,791 12.47 155.53 21.53
24 5,254 8.67  75.14 16.50
25 7,574 4.46 19.93 5.90
26 4,533 9.38 88.04 20.70
29 6,370 10.24 104.79 16.07
30 5,168 12.16 147.78 23.52
31 6,200 17.76 315.29 27.92
33 8,628 10.80 116.76 17.43
32 5,623 15.73 247.39 18.23
34 6,361 16.81 282.72 29.90
35 9,789 16.00 255.92 25.15
37 5,340 11.30 127.53 11.54
38 6,417 11.24 148.11 21.06
39 8,730 12.17 251.65 18.96
40 6,360 15.86 95.52 18.17
42 6,281 9.77 553.48 15.36
43 6,071 23.53 43.25 37.46
44 6,176 6.58 30.58 10.83
45 6,412 5.53 2.59 8.95
46 8,790 1.61 44.24 2.51
47 5,416 6.65 307.37 7.57
48 6,571 17.53 262.68 32.27
Z 8340 5,700 5.77 33.35 10.13
Z 8543 6,700 10.82 117.12 16.15

Ref.: 2Minimum significant difference (msd): 17.52 for alpha: 0.05

Table 3. Analysis of variance for the g.c.a. trial.
 
Fountain D.F. S.S Mid Square F Probability
Blocks 3 1648.19 549.398 3.49 0.0172 *
Treatments 52 34969.56 672.492 4.27 0.0000 *
Error 156 24540.71 157.312    
Non aditive 1 170.88 170.877 1.09 0.2988 NS
Residual 155 24369.84 157.225    
TOTAL 211 61158.47      

General average: 63.726. Total Sum per treatments: 13509.930. Total number of plots: 212.

Coefficient of variation : 19.68%. Categorical variables: Blocks 1-4 and Treatments 1.


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