Lomas de Zamora, Argentina
Universidad Nacional de Lomas de Zamora
Stability analysis for yield and expansion volume in popcorn hybrids --Burak, R, Broccoli , AM Popcorn culture is actually in expansion in Argentina, and native open-pollinated varieties have been replaced by simple hybrids introduced from the USA. Our work is focused on the study of adaptability for grain yield and popping expansion of these hybrids in a non-traditional region in the milk belt of Buenos Aires (Cuenca del Salado) at 34o 38’LS and 58o 48’ Long. 14 popcorn hybrids of current commercialization (H1-H14) were evaluated conducting 10 trials in 5 locations during 1998 and 1999, using standard experimental units. The variables analyzed were yield, grain yield per experimental unit (kg) and popping expansion or expansion volume (exvol), expanded volume of a 100 popcorn grain randomized sample within each experimental unit. Analysis of variance was made in a randomized complete block design , with a simple factorial including 14 treatments x 3 replications x 10 environments under the model:

yijk = µ+ b(E)jk + Gi + Ej + (G*E)ij + eijk

Here yijk is the observation of the kth replication of the ith genotype of the jth environment, m is the population overall mean, Gi is the fixed effect of ith treatment, Ej is the randomized effect of jth environment, (g*a)ij is the genotype x environment interaction effect, b(E)jk is the replications nested in environments effect and eijk is the experimental error randomized variable.

Stability analysis was made using bilinear regression models (Verma et al., 1978, Silva et al., 1985, Cruz et al, 1989). Each genotype is described by three parameters: two regression coefficients (b1 and b2) and the variance of regression deviation S2di. Coefficient b1 indicates genotype response in unfavorable environments and b1 + b2 measures response in the favorable ones. Environmental indexes are the independent variables of this multiple regression method and the zero value is the intercept of each one. The advantage of using this method is the ability to evaluate genotypes also under unfavorable environmental conditions. The model is:

E(Yij) = B0 + B1 Ij + B2Jj

Expected observation of the ith genotype in the jth environment, B0 is the mean for each genotype, B1 is the unfavorable environments regression coefficient, B1 + B2 is the favorable environments regression coefficient for each genotype, Ij = the environmental index (Eberhart and Russel, 1966), Jj = Ij(+) — Îj(+) the environment index of favorable ones minus their average.

The following matricial equation represents Yij values:

Xb + E = Y

The X matrix has three columns, the unity, the environmental effects, and thirdly, the favorable environmental effects minus its average. Unfavorable effects have zero value. b is the vector of the unknown regression coefficients and E is the vector of the experimental error for each genotype. Y is the vector of the observations. Applying the minimum square method we obtain the following system:

X'Xb = X'Y

( X' is the trans X matrix and b the regression coefficients estimations vector)

Table 1 shows genetic x environment significant effect results; effects for genotypes and environments also were significant.

Table 1. Analysis of variance for (YIELD) and (EXVOL) .(**p<0.01, *p<0.05).
 
S V / G L
Variables
Environments
9
Rep(Env.)
20
Treatments
13
Treat x Env
117
Error
260
VC(%)
(YIELD) 93.43** 0.631 0.822** 0.188** 0.097 12.34
(EXVOL) 22052** 1923.4 5707.4** 1461.6** 1154.2 9.09

Tables 2a and 2b show the environment average for each hybrid in two conditions: unfavorable (E(-) ) and favorable (E(+)). B0 is the overall mean including both environment conditions. The slopes (B) feature responses for genotypes on each environment (B1 y B1 + B2). R2 is the determination coefficient, which measures fitness for the model and Sdi is the regression device mean squares, measuring stability response of the hybrids. For each genotype, yield shows high R2 values; expansion volume (exvol) shows high R2 values except for H3, H9, H11 genotypes.

For yield, all genotype slopes are 1 despite the environment (Table 2a) However, for H1, H6 , H9, H10, H14, Sdi was significant. The hybrids differ not in their responses but in their stability. For the mentioned hybrids, behavior is not predictable on the environment range of this experiment.

Table 2a. Stability parameters for (YIELD).

Test t student for B1=1 y B1+ B2 =1 .(*p<0.05). Test F.(*p<0.05).
 
HYBB E(-) E(+) B0 B1 B2 B1+ B2 R2 Sdi
1 0.993 3.796 2.675 1.056 0.213 1.269 96.37 0.383*
2 1.006 3.757 2.657 1.035 -0.06 0.972 98.61 0.126
3 1.094 3.752 2.689 1.000 0.177 1.177 99.45 0.049
4 0.877 3.488 2.442 0.981 0.034 1.015 98.25 0.148
5 0.748 3.260 2.255 0.935 -0.275 0.660 97.67 0.166
6 0.981 3.491 2.487 0.947 0.021 0.968 94.51 0.450*
7 0.999 3.898 2.739 1.089 -0.664 1.023 99.16 0.084
8 0.732 3.583 2.442 1.066 -0.192 0.874 98.86 0.107
9 0.861 3.715 2.574 1.063 -0.117 0.945 97.58 0.233*
10 1.254 3.792 2.777 0.949 0.214 1.163 97.51 0.211*
11 0.901 3.506 2.464 0.979 0.175 1.154 98.74 0.11
12 0.850 3.200 2.260 0.885 0.078 0.963 98.95 0.073
13 0.893 3.659 2.553 1.040 -0.151 0.890 99.33 0.059
14 0.849 3.435 2.407 0.972 -0.048 0.924 97.34 0.218

Table 2b. Stability parameters for the variable (EXVOL).

Test t student for B1=1 y B1+ B2 =1 .(*p<0.05). Test F.(*p<0.05).
 
HYB E(-) E(+) B0 B1 B2 B1+ B2 R2 Sdi
1 351.87 389.14 366.78 1.034 -0.482 0.552 68.02 917.4
2 379.76 427.11 398.70 1.162 -0.448 0.713 53.18 2198*
3 351.39 370.47 359.02 0.455* -0.812 -0.357* 28.11 1013
4 325.11 386.80 349.79 1.397 -1.365 0.032 69.18 1517
5 362.61 405.17 379.63 1.021 0.042 1.062 58.18 1533
6 340.24 394.30 361.87 1.306 -0.018 1.288 57.27 2566*
7 347.59 394.94 366.53 1.261 -0.608 0.653 72.06 1122
8 352.17 395.50 369.50 1.036 0.051 1.087 72.63 830
9 388.16 397.56 391.92 0.221* 0.929 1.151 27.21 1229
10 372.86 425.49 393.91 1.354 1.101 2.455* 96.24 191
11 371.93 385.39 377.31 0.435* 0.263 0.697 24.94 1404
12 347.76 411.81 373.38 1.730* 0.710 2.440* 82.37 1476
13 361.87 390.29 373.24 0.651 0.201 0.852 45.98 1109
14 356.25 390.79 370.07 0.935- 0.435 1.370 66.25 1046

H10 and H7 had yield upper values in both environments, but H10 was unstable while H7 was stable and predictable in this evaluation (Fig 1). For exvol, genotype responses differ under unfavorable environments. For H3, H9 and H11 B1 <1 and for H2 B1>1. In favorable environments, for H3, B1+B2 < 1 while for H10 and H12 >1. Sdi was significant only for H2 and H6. Even when H2 showed the best popping expansion, H9 retained its capability in both environment situations, becoming better for this character (Fig. 2).

Table 3 shows means and the environment index for both variables. For yield, environments 1, 4, 5, 6, 3 and 2 were profitable, for exvol environments 7, 8, 1, 3 were. Instead of profitability of environment 1 for both characters, we found that a favorable environment for one is unfavorable for the other. This agrees with other classical studies describing a negative correlation between yield and expansion volume. These results contribute to aiding farmers in selecting better genotypes with yield stability, quality properties and adaptation for this no traditional zone.

Table 3. Means and environments. (+) favorable. (-) unfavorable.
 
Env (YIELD) (EXVOL)
  Mean Ij Ij(+) Mean Ij Ij(+)
1 4.41 (+) 1.88 0.81 390.4 (+) 16.71 -7.08 
2 3.56 (+) 1.03 -0.032 364.5 ( -) -9.19 -
3 2.66 (+) 0.13 -0.94 380.2 (+) 6.50 -17.29
4 4.26 (+) 1.73 0.67 362.7 ( -) -10.99 -
5 3.97 (+) 1.44 0.37 360.5 ( -) -13.21 -
6 2.71 (+) 0.18 -0.89 362.8 ( -) -10.88 -
7 1.13 ( -) -1.41 - 412.0 (+) 38.31 14.51
8 0.79 ( -)  -1.73 - 407.3 (+) 33.65 9.85
9 0.81 ( -) -1.72 - 346.1 ( -) -27.56 -
10  0.98 ( -) -1.54 - 350.4 ( -) -23.34 -

Figure 1. Genotype H7

Figure 2. Genotype H9
 
 
 
 


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