Search

Chilling requirement (CR) for bud dormancy completion determines the time of bud break in apple (Malus × domestica Borkh.). The molecular control of bud dormancy is highly heritable, suggesting a strong genetic control of the trait. An available Infinium II SNP platform for genotyping containing 8,788 single nucleotide polymorphic markers was employed, and linkage maps were constructed in a F1 cross from the low CR M13/91 and the moderate CR cv. Fred Hough. These maps were used to identify quantitative trait loci (QTL) for bud break date as a trait related to dormancy release. A major QTL for bud break was detected at the beginning of linkage group 9 (LG9). This QTL remained stable during seven seasons in two different growing sites. To increase mapping efficiency in detecting contributing genes underlying this QTL, 182 additional SNP markers located at the locus for bud break were used. Combining linkage mapping and structural characterization of the region, the high proportion of the phenotypic variance in the trait explained by the QTL is related to the coincident positioning of Arabidopsis orthologs for ICE1, FLC, and PRE1 protein-coding genes. The proximity of these genes from the most explanatory markers of this QTL for bud break suggests potential genetic additive effects, reinforcing the hypothesis of inter-dependent mechanisms controlling dormancy induction and release in apple trees.

Elionurus muticus is a native aromatic grass from the Pampa biome that produces an essential oil that is rich in citral. Despite the importance of citral, few studies have examined this species. The aims of this work were to evaluate the genetic structure and to characterize cytogenetically natural populations collected from Brazil. Genetic characterization was performed using AFLP markers, and cytogenetics assessed the chromosome number, karyotype and meiosis. The studied populations had genetic variability, especially within populations, indicating the possibility of selecting plants with relevant characters. High variability also suggests the preferential occurrence of outcrossing in natural populations. Regular meiosis was observed in the cytogenetic analysis with chromosome number 2n=20. The karyotype of the species is presented for the first time, with the karyotype formula 3sm + 4a + 1saSAT.

Genetic variability is the basis of plant breeding. In corn, a large and diverse genetic pool permits manipulation of different genotypes, but the genetic diversity of tropical germplasm has been little studied. With the objective of analyzing the amplitude of the genetic variability in 15 hybrids released in different periods by three different seed companies, phenotypic and molecular characterization was carried out in three environments and at two plant densities. The phenotypic assessment showed great similarity among the hybrids, suggesting that the breeding programs have developed genotypes with similar phenotypic traits. The dendogram of the molecular analysis showed clustering according with the different companies suggesting that each corn breeding program make use of different germoplasms. However, although the germplasm was different, it could be inferred that the selection pressure used by the breeders followed the same traits such as plant height, number of rows per ear and kernel weight among others analyzed in the present study, that contributed to the phenotypic uniformity of the genotype.O acesso e o uso da variabilidade genética de uma cultura são as bases do melhoramento de plantas. Em milho, um grande e diverso pool gênico permite a manipulação de diferentes genótipos. No entanto, a diversidade genética do germoplasma tropical ainda é pouco estudada. Com o objetivo de analisar a amplitude da variabilidade genética em 15 híbridos lançados em diferentes épocas e provenientes de três diferentes empresas de sementes, foi realizada a caracterização fenotípica e molecular dos genótipos em três ambientes e em duas densidades de semeadura. A avaliação fenotípica revelou uma grande similaridade entre os híbridos, sugerindo que os programas de melhoramento têm desenvolvido genótipos com caracteres fenotípicos semelhantes. A análise molecular, por sua vez, sugere que os programas de melhoramento de milho exploram germoplasma distinto, uma vez que o dendograma mostrou um agrupamento conforme as empresas. Entretanto, apesar de o germoplasma ser distinto, é possível inferir que a pressão de seleção utilizada pelos melhoristas tem seguido a mesma linha, isto é, há uma pressão de seleção por parte das empresas em relação a caracteres, tais como estatura de planta, número de fileiras de grãos e peso de grãos, entre outros analisados no presente trabalho, o que contribuiu para a uniformidade fenotípica dos genótipos.