A wide range of percent amylose and total percent starch has been reported among the major endosperm mutants, including ae, du, fl, fl2 h, o2, su, and su2. Multiple combinations of corn endosperm mutants affecting amylose-amylopectin ratios have been shown to have considerable genetic information. We studied the ten possible double combinations of endosperm mutant genes among 5 genes, including fl2, h, o2, su2, and du all in the inbred line W64A background. Interactions were studied through a diallel analysis (Table 1). A wide range of mean values for five variables measured was observed (Table 2).
Although differences among the ten double mutants were significant for all five variables, a Duncan multiple range test indicated no significant differences existed between any two means for the variables studied except percent amylose. Variance associated with general combining ability (GCA) for amylose synthesis was four times larger than for specific combining ability (SCA), and both were significant at the 1% level. We would suggest that the multiple combinations of endosperm mutants could be effective in upgrading percent amylose. Both GCA and SCA for percent starch were significant at the 5% level. Variance associated with GCA for 100 kernel weight was not significant; however, SCA for the same trait was significant. Specific gene combinations could change morphological traits.
GCA estimates of the endosperm mutant for the five variables reflect the general characteristics of each mutant involved in the double combinations (Table 3). The results imply an inverse relationship of percent amylose and percent starch, although the magnitude of the effect was different among the five mutants. The results could also suggest that it may be possible to find a favorable gene which is more efficient in total starch synthesis with no or little reduction in amylose synthesis. The incorporation of the selected favorable gene or genes and the ae gene may be considered as a possible step to increase both amylose and starch content.
The 10 double mutants were regrouped into 5 double mutant groups, each group representing one of the double combinations involving fl2, h, o2, su2, or du. The correlation coefficients for the 5 groups were computed separately (Table 4). It could also reflect the characteristics of the mutants involved in double combinations. A very high positive correlation between 100 kernel weight and starch weight/100 kernels for all the 5 double mutant groups was indicated. Correlations between percent amylose and percent starch were not significant or were significantly negatively correlated. It is not likely to upgrade both percent amylose and percent starch through double combinations of genes. However, in our data we could assume a possible candidate for incorporation with ae is the h gene, since it had the highest positive GCA estimate for percent starch and starch weight/100 kernels and also appeared to have no reduction in amylose weight/100 kernels. Correlation between percent amylose and percent starch was not significant for the double combination group involving h. We don't have data to support this assumption, and further studies should be conducted in this regard.
H. S. Chang and M. S. Zuber
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