The influence of the cob colour on the yields of flint and dent maizes

--Victor R. Corcuera*, Luis B. Mazoti and Carlos A. Naranjo

*Assistant Technician of C.I.C.

During the growing season 1990/91 two bulks were created at the Instituto Fitotécnico de Santa Catalina. Each one of these bulks was composed of a mixture of seeds of different flint and dent commercial hybrids. The purpose of creating these bulks was: 1. To keep a pool of genes useful for the later development of a breeding plan, through which it is expected to obtain commercial hybrids qualified for industrialization proceedings. 2. To focus on individual plants, genes, and on their diverse combinations.

This system definitely let us keep genes and increase the genetic variability through multiple recombinations. The last is possible, as pollination is not controlled within each bulk.

The bulks were grown in two different locations of the province of Buenos Aires: 9 de Julio and Chás. The first one has soils with a medium fertility degree, whilst the second has high fertility soils. Both bulks were grown during November, using a higher density of plants in Chás (50,000 plants/Ha) than in 9 de Julio (45,000 plants/Ha). At maturation the plants were harvested by hand, and samples were taken at random from each bulk. These samples belonged to flint and dent type in each case.

Thereafter, the samples were measured and analyzed at the laboratory through different descriptors recommended by IBPGR (International Bureau for Plant Genetic Resources). The traits/descriptors measured and evaluated in each ear were: 1. EL, ear length in cm; 2. ED, ear diameter in cm; 3. KR, number of kernel rows per ear; 4. NK, number of kernels per row; 5. EW, ear weight in g; 6. KW, kernel weight (g) per ear; and 7. %C, percentage of cob per ear.

In addition, the colour of the cob was considered for each ear measured. Then for each bulk, four groups of ears were evaluated as follows: flint type and white cob (FWC), flint type and red cob (FRC), dent type and white cob (DWC), and dent type and red cob (DRC).

Finally, the results obtained through the measurements practiced in nearly 600 ears were statistically analyzed.

Tables 1 and 2 show the commonest statistical measurements for each trait in both bulks (means, standard deviation, variability %, variance and range).

Table 1. Statistical measures for ear traits considering the coloration of the cob. (Chás bulk).
 
  Group EL ED KR NK EW KW %C
  FWC 17.49 4.24 14.02 34.83 166.97 137.10 18.10
  FRC 16.63 4.00 13.00 33.71 148.21 120.00 19.27
X DWC 17.62 4.56 15.20 35.20 204.00 161.00 21.22
  DRC 19.42 4.50 14.88 39.56 210.20 173.20 17.53
  FWC 1.97 0.23 1.56 4.51 34.98 31.05 3.88
  FRC 1.82 0.29 1.30 3.54 32.79 27.10 3.59
S.D. DWC 1.51 0.38 3.03 3.27 47.22 39.11 4.09
  DRC 1.48 0.36 1.83 2.93 43.93 35.26 3.62
  FWC 3.88 0.05 2.43 20.34 1223.60 964.10 15.05
  FRC 3.31 0.08 1.69 12.53 1075.18 734.41 12.89
G2 DWC 2.28 0.15 9.18 10.69 2229.73 1529.59 16.73
  DRC 2.19 0.13 3.35 8.58 1929.85 1243.27 13.10
  FWC 11.26 5.42 11.13 12.95 20.95 22.65 21.44
  FRC 10.95 7.25 10.00 10.50 22.12 22.58 18.63
Var % DWC 8.57 8.34 19.93 9.29 23.15 24.29 19.27
  DRC 7.62 8.00 12.30 7.41 20.90 20.36 20.65
  FWC 11.50 3.20 12.00 16.00 90.00 60.00 10.50
  FRC 12.70 3.60 10.00 28.00 70.00 50.00 14.30
Min. DWC 15.50 4.20 12.00 31.00 160.00 115.00 17.60
  DRC 17.00 3.80 12.00 35.00 135.00 110.00 11.80
  FWC 21.00 4.80 18.00 43.00 250.00 220.00 33.40
  FRC 19.30 4.40 14.00 39.00 200.00 160.00 28.60
Max. DWC 19.50 5.20 18.00 40.00 280.00 220.00 28.10
  DRC 23.50 5.50 18.00 46.00 320.00 250.00 25.00

Table 2: Statistical measures for each trait considering the coloration of the cob. (9 de Julio bulk).
 
  Group EL ED KR NK EW KW %C
  FWC 14.67 4.00 13.32 28.64 116.89 96.93 17.21
  FRC 15.44 3.89 13.36 30.89 121.38 100.42 17.34
X DWC 15.11 4.47 15.00 30.36 126.07 100.36 20.56
  DRC 14.07 4.32 13.95 28.73 116.22 94.30 19.31
  FWC 1.75 0.26 1.62 4.53 24.82 21.37 3.85
  FRC 1.82 0.20 1.45 4.38 22.93 19.67 3.32
S.D. DWC 1.33 0.29 1.71 4.94 34.20 28.38 3.67
  DRC 1.65 0.34 1.68 4.82 30.45 25.90 4.75
  FWC 3.06 0.07 2.62 20.52 616.03 456.68 14.82
  FRC 3.31 0.04 2.10 19.18 525.78 386.91 11.02
G2 DWC 1.77 0.08 2.92 24.40 1169.24 805.42 13.47
  DRC 2.72 0.11 2.82 23.23 927.20 670.81 22.56
  FWC 11.93 6.50 12.16 15.82 21.23 22.05 22.37
  FRC 11.79 5.14 10.85 14.18 18.89 19.59 19.15
Var% DWC 8.80 6.49 11.40 16.27 27.13 28.28 17.85
  DRC 11.73 7.87 12.04 16.78 26.20 27.46 24.60
  FWC 11.30 3.50 10.00 18.00 70.00 50.00 9.00
  FRC 12.00 3.60 10.00 24.00 80.00 65.00 12.00
Min. DWC 13.50 3.90 12.00 22.00 80.00 60.00 14.30
  DRC 11.00 3.50 10.00 19.00 60.00 50.00 10.00
  FWC 20.50 5.00 18.00 42.00 220.00 150.00 29.40
  FRC 20.00 4.40 16.00 43.00 180.00 150.00 30.00
Max. DWC 18.80 4.90 18.00 37.00 190.00 150.00 25.00
DRC 18.20 5.00 18.00 41.00 230.00 200.00 33.40  

Tables 3 and 4 show the existence of some statistically significant differences amongst the average values for each trait in each bulk.

Table 3: Differences between means for ear traits of the "Chás" bulk.
 
Group EL ED KR NK EW KW %C
FWC 17.49a* 4.24ac 14.02a 34.83a 166.97ab 137.10a 18.10a
FRC 16.63a 4.00b 13.00b 33.71a 148.21a 120.00b 19.27a
DWC 17.62a 4.56c 15.20ab 35.20a 204.00bc 161.00ac 21.22a
DRC 19.42b 4.50c 14.88c 39.56b 210.20c 173.20c 17.53a
*Individual means within a column followed by different letters are significantly different at 5% level.

Table 4: Differences between means for ear traits of the "9 de Julio" bulk.
 
Group EL ED KR NK EW KW %C
FWC 14.67a* 4.00a 13.32a 28.64a 116.89a 96.93a 17.21a
FRC 15.44b 3.89b 13.36a 30.89b 121.38a 100.42a 17.34a
DWC 15.11ab 4.47c 15.00b 30.36ab 126.07a 100.36a 20.56b
DRC 14.07c 4.32c 13.95c 28.73a 116.22a 94.30a 19.31b
*Individual means within a column followed by different letters are significantly different at 5% level.

From the detailed observation of the data given in the tables, it may be pointed out that:

1. In high fertility soils, dent maizes yielded more than the flints, though when one considers the low fertility situation (9 de Julio) there are not significant differences in yield between these two types (unless considering individual ears).

2. In high fertility soils, the DRC maizes were the highest yielding, and the FRC showed the lowest yields. The opposite occurs in low fertility soils.

Undoubtedly, the data and the general tendencies shown in this issue constitute an interesting fact, which will be deeply studied during the next growing seasons from this time on.

Furthermore, the multiple recombinations occurred in the field during the last growing season (90/91), and according to the results obtained, it can be pointed out that the coloration of the cob influences, although partially, the final yields.

The colour of the cob, as well as pericarp colour, is genetically determined by allelomorphs of the gene P. Thus, it would be convenient to study if there is some kind of association between this gene and the ones determining yield, though this is very complicated as it is a phenomenon of quantitative inheritance. If this fact could be effectively proved, the colour of the cob related to the endosperm texture might be considered in breeding plans to obtain commercial hybrids specifically developed for different areas with a different fertility degree of their soils as well.


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