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.
|40||3071/4||S3||flint||3, 23, 27, 28 y 33:plots of the tester Z8543|
|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.
Ref.: 2Minimum significant difference (msd): 17.52 for alpha: 0.05
Table 3. Analysis of variance for the g.c.a. trial.
|Non aditive||1||170.88||170.877||1.09||0.2988 NS|
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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