Conversion of elite inbred lines into Quality Protein Maize (QPM). 2003. / ConversÃo de linhagens elites em milho de alta qualidade protÃica (QPM).

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The current study was developed to evaluate the potential of the modified backcross procedure proposed by GuimarÃes et al. (2000), and the molecular markers to increase the efficiency in conversion projects of elite inbred lines into Quality Protein Maize. First, it was evaluated the association of the SSR markers umc1066, phi057 and phi112 with the opaque-2 gene, testing their effectiveness to distinguish O2O2, O2o2 and o2o2 genotypes in segregating populations derived from normal and QPM maize inbred lines. Thus, it was showed that the SSR markers were able to identify the recessive allele opaque-2, and that their effective use in marker-assisted selection will depend on the inbred lines used in the crosses and on the objectives of each project. Second, it was evaluated the applicability of RFLP and SSR markers in conversion projects of normal inbred lines into QPM, in which selection was employed in the BC2F1 and BC3F1 generations in two stages. First, heterozygous plants were identified by RFLP in each backcross generation, and then these plants were genotyped by SSRs in order to identify those with a higher proportion of the recurrent parental genome. This strategy was compared with conversion projects where only phenotypic selection was carried out. It was verified that the RFLP marker (EcoRI enzyme + probe 968 pb Opaque-2 gene) was efficient to identify and to early select the heterozygous genotypes in the backcross populations. However, considering the selection strategy and the population size evaluated, the identification of plants with higher recovery of the recurrent parental genome using SSRs did not increased the conversion efficiency, when compared to the projects where only phenotypic selection was employed. Furthermore, linkage drag was detected in the genomic regions flanking the opaque-2 and endosperm modifier genes. In a third study, experimental QPM hybrids obtained from the partial conversion of three elite inbred lines were evaluated. The results indicated that the QPM hybrids obtained by partial conversion of normal inbred lines presented a better protein quality and similar performance for most of the agronomic traits evaluated, including grain yield, when compared with the original hybrids. However, some of the problems specifically associated with QPM hybrids, such as higher lodging, thicker cobs and shorter grains, still remained up to this phase of the process. Both the normal versions and the converted QPM hybrids displayed a worst grain yield performance, when compared to the checks hybrids, indicating a loss in competitiveness in relation to these more recent hybrids.

ASSUNTO(S)

melhoramento genÃtico vegetal hibridaÃÃo. marcador molecular milho linhagem retrocruzamento melhoramento vegetal maize, plant breeding, molecular marker, line, backcross, cross

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