Lomas de Zamora, Buenos Aires, Argentina

Universidad Nacional de Lomas de Zamora

Association between yield components, grain morphological traits and volume expansion in popcorn hybrids cultivated in Argentina --Broccoli, AM, Burak, R Improvement in quality generally is considered the most important objective of popcorn breeding programs. Expansion volume, defined as the volume of popped corn per gram of unpopped corn, is the quality trait of greatest importance. High expansion volume is associated with increased kernel tenderness (Brunson, 1937). Also, from a commercial standpoint, popcorn genotypes with high expansion volumes will produce more popped corn than genotypes with low expansion volumes.

Compared to dent corn, popcorn kernels contain a high proportion of translucent (hard endosperm) relative to opaque (soft) endosperm. Starch contained in translucent endosperm expands upon heating, while starch contained in opaque endosperm remains relatively unchanged. (Hoseney et al, 1983). Willer and Brunson (1927) concluded that, of all kernel characteristics studied, the proportion of translucent endosperm was most highly correlated with expansion volume.

Popping expansion is a heritable character and the variability of individual ears within an open pollinated variety is similar to other cases of quantitative inheritance controlled by many genes. Significant correlations have been determined between popping expansion and size of kernel and proportion of soft starch, which are quantitatively inherited characters too.

Breeders could achieve popcorn desirable characters including all of the attributes of a good cultivar of flint or dent corn and must include high expansion volume and tenderness. Both characters seem to be closely correlated. The absence of a coarse hull and the presence of good flavor are also desirable.

Because of negative correlation between top yields and superior popping expansion it is difficult to combine both characters in the same genotype. So, some compromise must be made in either yield or popping expansion or both to secure the best results from the utility standpoint.

A smaller inbred depression occurs in popcorn when compared with dent corn. This possibility of finding comparative"per se" productive inbreds makes easy the simple hybrid seed utilization, largely in commercial production. This simplifies the seed production problems and makes possible a most uniform market product.

In Argentina, the traditional popcorns were open-pollinated varieties obtained from a wide range of genetic variability contained in native races.

With the advent of the MERCOSUR (global market of South America) the interest in this crop and the cultivated area increases substantially year by year, but the absence of locally achieved hybrids makes the commercial breeders import these genotypes principally from the USA.

Field trials at six enviroments of fourteen commercially available hybrids were carried out in order to evaluate yield components, popping expansion and genotype by enviroment interaction. To determine the relationships between some kernel characteristics and popping expansion (PE), kernel length (KL), width (KW), thickness (KTH),density of expanded (KED) and not expanded ones (KNED), were determined on a sample taken from the middle sector of the ear. Length (EL) and diameter (ED) of each one was measured. Yield (kg/ha) and prolificacy are positively correlated .

The correlation coefficients of popping expansion with these characters are presented in Table 1.

Table 1. Phenotipic correlations between the investigated traits. (*, **) Significant at the 0.05 and 0.01 probability, respectively.
 
  PE YIELD KTH KW KL ED EL KED KNED
YIELD *

-0.16

- - - - - - - -
KTH **

0.46

-0.11 - - - - - - -
KW 0.09 -0.02 **

0.32

- - - - - -
KL **

-0.18

**

0.52

-0.03 **

0.18

- - - - -
ED *

-0.15

**

0.51

-0.01 -0.02 **

0.57

- - - -
EL -0.01 **

0.55

**

0.23

**

0.17

**

0.37

**

0.48

- - -
KED 0.02 **

0.21

-0.08 -0.09 0.12 **

0.19

**

0.21

- -
KNED **

-0.98

*

0.15

**

-0.46

-0.11 **

0.19

*

0.16

0.01 -0.014 -
PI 0.03 **

0.32

**

0.19

*

0.17

0.11 0.011 **

0.28

0.004 -0.04

As expected, high positive correlation coefficients of yield with components like KL and KDI exist. PI was also strongly associated because of some hybrids' tendency to produce two ears of uniform type. In agreement with current bibliography, yield components have a negative association with popping expansion, so it is difficult for the breeders to achieve hybrids with both characters simultaneusly.

Analyzing kernel morphological traits, there appears to be some definite association with PE and kernel size and shape. A high positive correlation (r = 0.46**) was verified with KTH and a negative one with KL (r = -0.18**).

Measuring densities of kernels, initial or without expanding KED has no correlation with KNED, but final density of the expanded kernels KNED has a strong association (r =0.93**) and would be an effective selection criterion.

These data are in agreement with basic information, even though the hybrids evaluated may be related because of the common origin of some of them, and certainly there is a restricted genetic base that includes some of the best American lines previously evaluated in many Argentine enviroments.
 
 


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