Maize
Genetics Cooperation Newsletter 80. 2006.
Centro de Investigaciones Geneticas (CIGEN)
University of Buenos Aires
Renessen Seeds
Since the old days, plant breeding has contributed to the increase in content of nutritional elements, as well as to improving the efficiency of their production. Nevertheless, the conscious improvement of nutritional elements may be considered a more recent goal in plant breeding. In 1990, a maize quality breeding program was initiated at the CIGEN, which is located in Llavallol in the province of Buenos Aires, Argentina (22 m.a.s., 34�48�S; 58� 31�W), aimed at developing and selecting high oil, high protein, high starch and high quality protein inbreds for further development of quality single crosses. During the first stage of the program, several maize inbreds were developed, tested and selected following the classic methodology. These inbreds carry single recessive genes (wx, o2, o5, O9, O11, sh4) or may be double recessive (wxsh4; wxo2). Moreover, high oil inbreds were also selected during this phase. In the following stage of breeding, single-cross hybrids were obtained and tested in several complete randomized block design field trials with three replicates conducted in Llavallol. The experimental unit was a 5.5 m long row. The experimental hybrids tested were named from CIG 1 to CIG 104. During the last three years (2003, 2004 and 2005) protein, starch and oil content, as well as kernel density, were evaluated in F2 kernels from a total of 104 single crosses by near infrared reflectance (NIR) using a Tekator Infrated 1227 device. The field trials were kept in isolation from other maize to prevent the influence of foreign pollen on oil content, and protein and starch quality.
In 2003, all hybrids were evaluated in field trials and the results are presented in Table 1. Later, in 2004 and 2005, only eighty and sixty-three single crosses were tested respectively (see Tables 2 and 3). Certainly, the greatest variation among genotypes is for oil and protein content, as the coefficient of variation obtained for starch content and kernel density is truly very low. Only seven hybrids were studied during the three growing seasons. Forty-eight single-cross hybrids were evaluated for two years and the remaining forty-nine crosses were only studied for one year.
Table 1. Results for 104 hybrids evaluated during the first year of trials (2003).
|
|
avg. �
s. |
variance |
c.v.% |
min. |
max. |
|
protein |
9.97 �
0.92 |
0.85 |
9.23 |
8.7 |
12.1 |
|
oil |
5.08 �
0.40 |
0.16 |
7.87 |
4.28 |
6 |
|
starch |
71.6 �
1.13 |
1.28 |
1.58 |
69.1 |
74.1 |
|
density |
1.27�
0.03 |
0.17 |
2.36 |
1.21 |
1.31 |
Table 2. Results for 80 hybrids evaluated during the second year of
trials (2004).
|
|
avg. �
s. |
variance |
c.v.% |
min. |
max. |
|
protein |
10.5 �
0.95 |
0.9 |
9.09 |
8.4 |
12.9 |
|
oil |
5.4 �
0.48 |
0.23 |
8.89 |
4.48 |
6.04 |
|
starch |
70.4 �
0.99 |
0.98 |
1.4 |
68 |
72.8 |
|
density |
1.29 �
0.01 |
0.0001 |
0.78 |
1.25 |
1.31 |
Table 3. Results for 63 hybrids evaluated during the third year of
trials (2005).
|
|
avg. �
s. |
variance |
c.v.% |
min. |
max. |
|
protein |
11.45
� 0.78 |
0.61 |
6.81 |
9.3 |
13.1 |
|
oil |
5.36 �
0.5 |
0.25 |
9.33 |
4.49 |
6.89 |
|
starch |
70.5 �
1.21 |
1.46 |
1.72 |
68 |
73.8 |
|
density |
1.27 �
0.04 |
0.002 |
3.15 |
1.07 |
1.32 |
The average protein content in the whole kernel does not differ significantly among five hybrids studied from 2003 to 2005: CIG6, CIG9, CIG42, CIG58 and CIG59 (ANOVA, F6-12: 0.40; p: 0.87). Nevertheless, highly significant differences in the protein content of each single-cross were detected among years (ANOVA, F2-12: 4.35; p: 0.04), and two different groups were detected through the least significant differences test (LSD, D: 0.937; t12: 2.18; Sx: 0.430; p: 0.05). The differences found in relation to oil content among the seven genotypes evaluated for three consecutive years (ANOVA, F6-12: 2.45; p: 0.09) made it possible to also differentiate two groups (LSD, D: 0.562; t12: 2.18; Sx: 0.258; p: 0.05). No significant differences among years for the same genotype were found in relation to oil content (LSD, D: 0.368; t12: 2.18; Sx: 0.169; p: 0.05).
In relation to the 48 single crosses evaluated for two years, the results showed highly significant differences among genotypes for protein content (ANOVA, F47-47: 1.88; p: 0.016) and also for oil content (ANOVA, F47-47: 1.30; p: 0.18). These hybrids may be divided into nine groups in relation to their protein content (LSD, D: 1.5602; t47: 2.012; Sx: 0.776; p: 0.05) or into seven groups if oil content is considered (LSD, D: 1.03; t47: 2.012; Sx: 0.513; p: 0.05). Protein content differs very significantly through the two years of evaluation (ANOVA, F1-94: 17.37; p: 0.000) and two groups may be distinguished (LSD, D: 0.319; t47: 2.012; p: 0.05). No differences were found in relation to oil content between years (ANOVA, F1-47: 0.11; p: 0.74). No variation (c.v.: 0%) was observed in the oil content of hybrids CIG11, CIG22, CIG38 AND CIG53 through the period evaluated. Therefore, these single crosses containing 4.8% to 6.0% oil may be considered to be very stable for the trait. No significant correlations were found between oil and protein content (r: 0.12). Nevertheless, significant correlations exist between: oil-starch (r: -0.24; p: 0.05); starch-protein (r: -0.71; p: 0.05); oil-density (r: -0.35; p: 0.01) and starch-density (r: -0.53; p: 0.05). The protein content observed in the F2 kernels of the single-cross hybrids studied (e.g.: 13.1% in CIG21, see Tables 1 to 3) is certainly high in relation to the average content of the commercial hybrids commonly grown in Argentina.
The results obtained to this point, reinforced by a significant variation among years for protein content in most of the genotypes, strengthen the already known fact that environment and genotype x environment interaction are extremely important in the determination of this trait. Nevertheless, in spite of this fact, a high level of protein content in F2 kernels resulted from using a very high protein content inbred as female parent. Whether or not most of the single-cross hybrids tested have a high protein content (10.5% to 13.1%) and also a high starch content (70% to 72%), all of them have a high oil content (³ 4.4%).
The
great quality of these single-cross hybrids, accompanied by their performance
and phytosanitary behaviour, will facilitate their use for animal feed and for
obtaining high value-added consumer goods in the near future.
_________________________________________________
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