Teosintes have pericarps and aleurone layers that are thinner than maize. The pericarp especially is thinner, since maize has a considerable variation in aleurone layer thickness. In order to study the inheritance of these characters in hybrids between perennial teosinte and maize (Gaspe), we analyzed the results obtained which, up to now, come from measurements made on Gaspe, Zea perennis and F2 kernels from reciprocal crosses between both parents.
Kernels were prepared for measurement according to Tracy et al. (MNL 52:60, 1978). Pericarp and aleurone layer thickness were evaluated on 20 Gaspe and perennial teosinte kernels, making 5 measurements on each. These traits were also evaluated on 100 F2 reciprocal grains (50 of Gs x Zp and 50 of Zp x Gs). Results obtained are shown in Table 1. Perennial teosinte has less than one fourth the pericarp thickness of Gaspe. The F1 reciprocal pericarp thickness is significantly different, probably pointing out some cytoplasmic effect on character expression. Thin pericarp (perennial teosinte) is partly dominant over thick pericarp (Gaspe). F1 pericarp thickness is nearer to the parental than to perennial teosinte, thus it may be inferred that the wild character (thin pericarp) does not behave as a dominant.
It is important to remark that in both reciprocal F1's the pericarp thickness is a highly variable character (range: 15 to 70 microns). This points out that: 1) gametes with different information for pericarp thickness are brought in by perennial teosinte, and 2) pericarp thickness does not have simple inheritance but the action of genes with additive effect prevails. It is also appropriate to point out that thin pericarp is not associated with enclosed kernels, as it can be observed that every F2 grain is enclosed in a fruit case like Z. perennis, but has pericarp thickness similar to maize. In short, the enclosed-naked kernel character segregates independently from thick-thin pericarp character.
From the analysis of aleurone layer data, it must be especially remarked that in this particular case, perennial teosinte's aleurone layer is thicker than maize's (Gaspe). No significant difference was found on means in reciprocal F2, according to crossing direction. That is to say, no cytoplasmic effect is detected. The mean thickness of aleurone in F2 kernels is superior not only to that of the parent but also to the thicker parent (Z. perennis). This may occur because in hybrids between perennial teosinte and Gaspe a particular phenomenon takes place: high frequency production of kernels with multilayer aleurone. The frequency distribution of aleurone layer thickness in F2 kernels is transgressive in the positive direction and varies from 36 to 143 microns. Preliminary results allow distinguishing not only between maize and its wild relatives, but also between different teosintes, and seem to point out that they are the consequence of quantitative inheritance and not associated to the enclosed-naked kernel characteristic.
Table 1: Pericarp thickness (PT) and aleurone layer thickness (AT) in perennial teosinte (Zp), Gaspe (Gs) and their reciprocal F1 and F2 (thickness in microns)
Luis M. Bertoia and Jorge L. Magoja
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