High-quality protein maize with normal genotype: Inheritance of lysine content

Previous reports (MNL 52:37, 1978 and 55:66, 1981) presented the finding of high-quality protein maize (high content of lysine) without the use of mutants which modify the structure of the endosperm, such as opaque-2. These maizes, obtained by the selection of the progeny as a result of crossing a normal line with floury-a of high lysine, have normal phenotype (hard endosperm) and are of "normal genotype" because they do not have in their genetic background any floury mutant.

The purpose of this work is to report preliminary experiences, performed with the aim of interpreting the inheritance of the lysine level in these normal maizes.

A line of maize (red flint), with high level of lysine in the endosperm (3.2g/16gN) was crossed with another normal line of low content (2.3 g/16gN). The segregation among 112 F2 kernels, analyzed by its lysine content in the endosperm is shown in Figure 1. This kind of segregation can be interpreted as the effect of dosage in the endosperm, of two independent genes which accumulate their individual effects. According to this criterion 1/16 of the F2 kernels would have no active allele, 3/16 two, 4/16 three, 3/16 four, 2/16 five and 1/16 six--the last ones being of the same high level of lysine as the progenitor of high lysine.

The segregation in the lysine level found among F2 kernels can be explained by the effect of cumulative dosage for two major genes which segregate independently. These two genes would be the ones that were previously referred to as lysine-1 and lysine-2 (MNL 52:37, 1978). Actually, the real situation is that these genes repress by the effect of dosage, in a greater or lesser extent, the synthesis of zein (MNL 55:66, 1981). Consequently, the level of lysine varies, the content for this amino acid in the absence of repression being normal, and maximum when the individual repressive effects of the six active alleles are combined. The intermediate lysine levels, between the progenitor extremes, are a consequence of intermediate levels of zein (Magoja et al., Mendeliana V (2), 1981, in press).

The results presented here are incomplete because they were performed in only one F2 ear. Actually we are studying other F2 segregations and also the backcrosses with the same line with high lysine content and "normal genotype" employed in the current paper, but also with other selected lines with greater lysine content (3.6 g/16gN). These lines are of the red flint type of maize.

We can consider from the results obtained up to now that, in the inheritance of the level of lysine in these normal maizes, at least two major genes might be involved, but perhaps there might also exist small effects of other modifiers. It can be considered from the experiments performed that the lysine level of maize endosperm can be improved without the use of mutants that modify the structure of the endosperm.

Figure 1.

Jorge Luis Magoja and Angel Alberto Nivio


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