Isoenzymatic variation in the germplasm of Brazilian races of maize (Zea mays L.)

Abstract

There are more than 200 races of maize (Zea mays L.) divided into three groups (ancient commercial races, the recent commercial races, and indigenous races). Although the indigenous races have no commercial value, they have many important characteristics which can be incorporated into maize breeding programs. Most Brazilian indigenous germplasm race stocks were collected at least 40 years ago, and nothing is known of the genetic variability present in this germplasm. The genetic variability was assayed in 15 populations from four indigenous races of maize (Caingang, Entrelaçado, Lenha and Moroti) and five indigenous cultivars, using five isoenzymatic systems encoded by 14 loci. The analysis revealed a low level of variability among the samples studied. Overall, the mean number of alleles/polymorphic locus was three, 64.3% of the loci analyzed being polymorphic and the estimated heterozygosity was 0.352. The mean number of alleles/polymorphic locus per population was 1.6. A mean of 47.5% of the loci were polymorphic. The mean expected heterozygosity was 0.195, the mean genetic identity was 0.821 and the proportion of total genetic diversity partitioned among populations (Gst) was 0.156. A founder effect could explain the low variability detected.<br>Existem mais de 200 raças de milho (Zea mays L.), as quais são divididas em três grupos (raças comerciais antigas, raças comerciais recentes e raças indígenas). As raças indígenas, embora não tenham valor comercial, possuem muitas características importantes que podem ser utilizadas em programas de melhoramento de milho. A maior parte do germoplasma brasileiro das raças de milho indígena foi coletada, no mínimo, 40 anos atrás e nada é conhecido sobre a variabilidade presente neste germoplasma. Quinze populações de 4 raças indígenas de milho (Caingang, Entrelaçado, Lenha e Moroti) e 5 cultivares indígenas foram analisados utilizando-se 5 sistemas isoenzimáticos codificados por 14 locos. A análise revelou um baixo nível de variabilidade entre as amostras estudadas. O número médio de alelos/loco foi três, com 64,3% de locos polimórficos e uma heterozigosidade média esperada de 0,352. Por população, a média de número de alelos por loco polimórfico foi 1,6, em média 47,5% dos locos foram polimórficos e a heterozigosidade média foi 0,195. A distância genética média entre as populações foi 0,821 e a proporção da variabilidade genética, que é atribuída ao componente entre populações (Gst), foi 0,156. Os dados sugerem que um efeito de fundador poderia explicar a baixa variabilidade detectada

Genetic diversity among maize (Zea mays L.) landraces assessed by RAPD markers

“…In contrast, two other accessions, Astecão Branco and Asteca Branco that have been treated by similar names were less related by RAPD showing a similarity of 0.85. Gimenes and Lopes (2000) reported similar results by using isoenzyme analysis. The authors studied 15 maize populations derived from three indigenous maize races and observed that there was no connection between the accessions name and the genetic relationships.…”

Inter- and intra-population variation of local maize (Zea mays L.) populations from Slovakia and Czech Republic

“…Based on the quantitative evaluation of isoenzyme diversity of the Slovak and Czech local maize populations they appertain into the range of populations originating from other areas. This is confirmed for instance by the studies of Brazilian and other tropical maize populations where average numbers of alleles per loci were lower than within our populations -1.6 and 2.0-2.4, respectively (Gimenes & Lopes 2000;Pinto et al 2003). This parameter is also generally affected (decreased) by a low number of analyzed populations (Dubreuil & Charcosset 1998).…”

“…Nevertheless, differences were observed in the frequency of alleles. The low frequency of allele acp1:3 (1.5%) in our populations is similar to Spanish (Lefort- Buson et al 1991) and other European populations (Llaurado et al 1993) and very different from the frequency of this allele in western African (Sanou et al 1997), south-western U. S. (Doebley et al 1988), and Brazilian (Gimenes & Lopes 2000) ones. The almost identical status in comparison with those populations was in the frequency of allele Mdh1:1, less frequented was allele Mdh5:15 and more frequented was allele Pgd1:2.…”

“…High heterogeneity within the analyzed Slovak and Czech local populations could be an effect of grower practices and isolation distances used in the years 1950-1970. The expected heterozygosity (He) revealing both allele numbers and allele frequencies ranged from null to 0.492 (locus acp1) with an average of 0.197 (Table 1), which is less than average He in southwestern Chinese (0.29) (Lu et al 2002), U.S. (0.46) (Kahler et al 1986), Bolivian (0.23) (Goodmann & Stuber 1983) or Mexican (0.21) (Doebley et al 1985) but similar to Brazilian (0.195) (Gimenes & Lopes 2000) populations. Considering that 15% of alleles were rare in the Slovak and Czech local populations a lower level of heterozygosity is explainable by this fact.…”

Isoenzymatic variability in tropical maize populations under reciprocal recurrent selection

“…Maize is one of the major crops in which the genetic variability has been extensively studied at the isoenzymatic level (Doebley et al, 1985;Kahler et al, 1986;Llauradó et al, 1993;Sanou et al, 1997;Gimenes & Lopes, 2000). The simplicity of the isoenzyme assays together with the lower cost, still guarantees its use today (Liu et al, 2001).…”