Perennial teosinte-Gaspe hybrids: inheritance of pericarp, thickness

Pericarp thickness is a fruit trait that allows differentiation not only between maize and teosinte but also within teosinte (MNL 59:61, 1985). The aim of this article is to amplify on the data we have presented (MNL 59:68, 1985) on pericarp thickness in hybrids between perennial teosinte (Zea perennis) and maize (Gaspe). As previously pointed out (MNL 59:68, 1985) pericarp thickness was studied in 20 plants of perennial teosinte, 20 plants of Gaspe, 50 plants F1 (Gs x Zp), 50 plants F1 (Zp x Gs) and 150 plants F2 (Zp x Gs).

Although it seems unnecessary, it is important to remark that as the pericarp is maternal tissue, evaluation was performed on F2 kernels (F1 pericarp) and F3 kernels (F2 pericarp). The study was carried out considering individual plants from each of the 5 populations analyzed. As shown in Table 1, Gaspe has more than four times the pericarp thickness of perennial teosinte. Variability is low in both parents, probably pointing out lack of environmental effect over phenotypic expression. Reciprocal F1 averages as well as F2 are similar. The variation range and phenotypic variation coefficient are close.

The results presented in Table 2 show that the main variation is genetic and therefore the heritability of this character calculated from these data is high (0.80). The trait variability that can yet be observed in both reciprocal F1s is similar to that from F2. Consequently this led us to think that pericarp thickness "segregates" within F1 plants. This particular phenomenon, that can be attributed to metaxenia, may be explained upon the basis of the marked influence exerted by the underlying genotype (F2 seed) upon F1 pericarp thickness. The germ or the endosperm or both (products of genetical recombination) present several F2 genotypes, and probably these tissues may produce some metabolite which may influence pericarp thickness during kernel development. The fact that all F2 kernels may have a F1 pericarp with the same genotype led us to suppose "a priori" that this genotype ought to express a unique phenotype (thickness more or less constant). The only acceptable explanation, since there is low environmental influence on this character (as it is expressed in the parents) is metaxenia phenomenon. Metaxenia has been demonstrated on fruit traits in other vegetable species such as the genus Solanum (Andeew, 1969), apple (Kovacs, 1976) and palm (Ream, 1978). Such as in our case, Andeew (1969) pointed out that metaxenia is produced in hybrids between species genetically far apart.

Comparison among average values of pericarp thickness for the studied populations are shown in Table 3. No significant differences can be detected between F1 in relation to F2. This fact reinforces the hypothesis that the trait "segregates" in F1 generation (F1 pericarp and F2 seed).

Figure 1 shows the distribution of frequencies of the studied trait. It can be observed that F1 and F2 distributions are similar, moving towards the left, that is to say towards perennial teosinte. This fact together with the results given in Tables 1 and 2 points out strongly that thin pericarp (perennial teosinte) partially dominates over thick pericarp (maize). It is important to remark that those F2 kernels (F1 pericarp) developed on F1 plants of this interspecific cross, are wholly enclosed in fruit cases such as perennial teosinte. Despite this fact there is thickness segregation, whereby, as was reported previously (MNL 59:68, 1985), pericarp thickness segregates independently from naked/enclosed kernels.

In short, the results obtained point out that: 1) pericarp thickness is quantitatively inherited, 2) thin pericarp is partially dominant over thick pericarp, 3) there is predominance of genes with dominant and also with additive effect, and 4) metaxenia effect conditions trait "segregation" in F1 generation.

Tables 1 and 2.

Table 3 and Figure 1.

L.M. Bertoia and J.L. Magoja
 
 


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