Perennial teosinte-Gaspe hybrids: specific relationship of endosperm protein content

Kernel protein content in wild relatives of maize is higher than in the cultivated species. In most cases it is twice the normal content of maize. Endosperm protein content (EPC) is a specific character of Zea taxa (see "Fruit traits" in a previous report in this MNL), apparently associated with other fruit morphological characteristics. The aim of this research is to investigate if EPC is associated with other morphological traits in plants derived from interspecific crossing. Hybrids between Z. perennis and Gaspe are a suitable material for this study: EPC is 24.1% in Z. perennis whereas in Gaspe it is 14.4%.

In general, individuals of F2 and F3 progeny resulting from crosses between Z. perennis and Gaspe have a high EPC, approximating that of Z. perennis.

Thirty four plants that stood out for their definite phenotype: 1) teosintoid, 2) intermediate and 3) maizoid were taken from F2 and F3 populations to study EPC association to other characters. Teosintoid phenotype belongs to those plants that combine mainly perennial teosinte traits: perennial, distichous spike, single spikelets, distichous tassel central spike, high number of tillers, enclosed kernels and narrow leaves. Maizoid phenotype belongs to those plants that combine mainly maize characteristics: annuals, polystichous ears, paired spikelets, polystichous tassel central spike, few tillers, naked kernels and wide leaves. Intermediate phenotype belongs to those plants in which the furthest phenotypic traits are combined. Based on each plant, EPC was analyzed. The average results discriminated by phenotypes are given in Table 1. Teosintoid plants have the same EPC as perennial teosinte, whereas maizoid plants are significantly lower than teosintoid, but superior to Gaspe. EPC of intermediate phenotypes is also intermediate, but no statistical difference was detected when compared with the extreme phenotypes.

These results point out a significant association, although it is not the expected one, between EPC and plant phenotype. Maizoid plants retain a high protein content. When association between EPC and plant individual characteristics is analyzed it may be inferred, as shown in Table 2, that: 1) those plants with later pollen production have high EPC; 2) those plants with a high number of tillers have high EPC; 3) those plants with distichous spikes have higher protein content than those with polystichous ones; 4) those plants with single female spikelets have higher EPC than those with paired ones; 5) plants whose spikes have a low number of kernel rows have high protein content. Despite the fact that the variation amplitude of EPC is not that which might be expected, a clear association between EPC and some specific characters exists within the restricted variability. Since this is a significant association, it can be stated that EPC is a specific trait, linked to other morphological characteristics that distinguish maize from perennial teosinte.

It is interesting to mark the fact that, even in those plants whose phenotype is clearly maizoid, the protein content is maintained considerably high. This suggests that high protein content transference into maize might take place without great inconvenience, although this high protein content may not be completely retained in maize. The fact that EPC is not wholly associated with specific traits suggests that a good part of the genes of the polygenic complex that conditions protein content segregate independently, and most of them may be dominant instead of having additive effects.

Table 1: Endospem protein content of different phenotypes

Table 2: Correlation coefficients (r) between endosperm protein content (EPC) and several mornholopical traits. *-- significant at 5 % level, **-- significant at 1 % level.

Liliana Ferrari and Jorge Luis Magoja


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