More about Gaspé germplasm for red flint corn improvement

--Mónica B. Aulicino and Jorge L. Magoja

In the last years, Argentina has expanded the maize cultivation areas to larger latitudes. Early hybrids must be used because of their precociousness, low thermal requirements and quick grain ripeness. They are foreign corns mainly of the dent type.

We are interested in developing precocious materials with red flint kernel type. These cultivars could better respond to Argentine production and would be adapted to the new cultivation areas.

This research started evaluating the ability of Gaspé as a precocity donor (see Aulicino, MB and Magoja, JL, MNL 65:40). It is necessary to know the possibility of introducing precocity from Gaspé into red flint inbreds with normal evolutive cycle.

Seven inbred lines of red flint corn were used in the present experiment: P465, P1338, H38, AD3, P21 obtained from INTA Pergamino, and DYW and CFE from Llavallol. These have been maintained by selfing and it is assumed that they are homozygous.

The inbred lines were used as female parents (P2) and Gaspé as the male (P1). Several F1's were obtained from these crossings. Likewise, other generations are derived from F1 individuals: F2 @ (by selfing) and F2 sib (by crossing "inter se" F1 individuals). The backcrosses were obtained by crossing F1's x Gaspé (BC1) and F1's x lines (BC2).

The following traits were evaluated in parents and in the other generations: days to tassel from planting (T), plant height in cm (PH), ear insertion height in cm (EIH), stalk diameter in cm (SD), number of rows per ear (NRE), number of kernels per row (NKR), ear length in cm (EL), ear diameter in cm (ED), kernel weight per ear in g (KWE). Means (X), standard deviation (SD) and phenotypic variation coefficient (CV%) were calculated (Table 1).

Table 1. Means (X), standard deviation (SD) and coefficient of variation (CV %).
 
    P1 P2 F1 F2 @ F2 sib BC1 BC2
  X 40.62 68.67 54.33 57.29 56.29 49.96 62.62
T SD 1.03 4.32 1.74 1.99 2.07 1.90 3.47
  CV% 2.54 6.29 3.20 3.47 3.68 3.80 5.55
  X 88.00 191.44 170.11 151.39 160.93 126.43 180.19
PH SD 3.06 20.01 10.94 11.56 9.90 11.98 12.91
(cm) CV% 3.48 10.45 6.43 7.64 6.15  9.48 7.16
  X 13.62 79.74 51.09 47.66 49.95 28.70 66.05
EIH  SD 1.70 12.52 6.97 8.32 7.52 5.62 10.36
(cm) CV% 12.49 15.70 13.64 17.46 15.06 19.60 15.66
  X 1.35 1.42 1.41 1.35 1.43 1.30 1.36
SD SD 0.05 1.19 0.14 0.14 0.10 0.18 0.11
(cm) CV% 3.92 13.13 9.70 10.70 7.55 13.97 8.10
  X 9.32 12.73 11.23 11.79 11.68 10.86 12.28
NRE SD 0.42 1.09 0.66 0.85 1.01 0.82 1.07
  CV% 4.55 8.54  5.89  7.18 8.6 7.52 8.75
  X 17.14 23.28 24.67 19.97 21.53 18.85 23.98
NKR SD 1.90 6.44 4.38 2.36 3.59 3.88 4.54
  CV% 11.10 27.65 17.75 11.83 16.68 20.56 18.92
  X 11.24 13.51  13.61 11.7 12.61 11.40 13.16
EL SD 0.79 2.78 1.55 1.26 1.51 1.75 1.73
(cm) CV% 7.03 20.58 11.40 10.25 11.98 15.37 13.13
  X 3.08 3.56 3.50 3.45 3.46 3.41 3.55
ED SD 0.08 0.15 0.16 0.21 0.18 0.18 0.22
(cm) CV% 2.49 4.13 4.48 5.96 5.32 5.36 0.34
  X 19.70 52.94 45.62 31.88 38.09 26.78 44.62
KWE SD 4.28 24.07 7.89 7.13 8.21 9.71 13.94
(g) CV% 21.72 45.47 17.29 22.38 21.56 36.2 31.94

See abbreviations in the text.

Two techniques for estimating heritability were used:

a. Method of parent-offspring regression (%H): A coefficient of regression was calculated using sib means of F2's, derived from different crosses over the phenotype values of F1's. The b's calculated are the %H (Table 2).

Table 2. Heritability (%H), method of parent-offspring regression.
 
  T PH (cm) EIH (cm) SD (cm) EL (cm) ED (cm) NRE NKR
%H 28.41 62.93 54.76 26.66 5.77 59.73 34.73 5.50

See abbreviations in the text.

b. Method of the backcrosses (h2): This method estimates the heritability using the variances of the segregating populations (F2) and both of the backcrosses, see Warner (Agron. J. 44:427-430, 1952). It allows estimations of additive variances. The efficiency of any plant breeding program depends upon their relative magnitudes (Table 3).

Table 3. Heritability (h2), method of the backcrosses.
 
  NRE EL (cm) ED (cm) NKR SD (cm) EIH (cm) PH (cm)
P465 <0 <0 <0 <0  0.67 0.82 0.10
H38 0.49 <0 0.58 <0 0.28 0.11 0.28
P1338 0.32 0.14 0.25 <0 <0 0.81 0.76
AD3 0.83 0.25 0.82 0.29 <0 0.99 0.2
DYW 0.53  0.39 0.37 0.58 <0 <0 <0
CFE <0 0.54 <0 <0 0.75 <0 <0

See abbreviations in the text.

The heritability values calculated for most of the traits show that the greatest part of the variation is genetic, especially for PH, EIH and ED. Nevertheless, the traits T, SD and NRE overtook greater values than 25%.

The heritability values (h2) calculated for NRE and EP traits in the materials derived from H38, P1338, AD3 and DYW were in agreement with the %H values found. The negative values (<0) could be explained by genetic inference of the parents on their backcrosses. All the same, the parents are capable of modifying the variance values of their backcrosses in a non-predictable manner. This fact explains the differential behavior of the inbred lines with respect to Gaspé germplasm.

Some ear and plant traits were positively correlated with earlier tasseling date (P). Furthermore, high heritability values obtained point out that selection will be effective for them. This will ensure a positive advance in future breeding.


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