Variabilidade isoenzimática em populações tropicais de milho sob seleção recorrente recíproca

O milho (Zea mays L.) é uma das culturas em que a variabilidade genética tem sido extensivamente estudada com base em locos isoenzimáticos. A variabilidade genética das populações de milho BR-105 e BR-106, e dos sintéticos IG-3 e IG-4, obtidos após um ciclo de seleção recorrente de elevada intensidade, foi investigada para sete locos isoenzimáticos. Foram identificados 20 alelos, sendo que a maioria dos alelos exclusivos foi detectada na população BR-106. Um ciclo de seleção recorrente recíproca (RRS) causou reduções de 12% no número de alelos em ambas populações. Mudanças nas freqüências alélicas foram observadas entre populações e sintéticos, principalmente para o loco Est 2. As populações mostraram similaridade para número de alelos por loco, porcentagem de locos polimórficos, e para heterozigosidade observada e esperada. Houve decréscimo nas estimativas da variabilidade dos sintéticos em conseqüência dos efeitos da deriva genética e redução do tamanho efetivo populacional. A distribuição da diversidade genética dentro e entre as populações revelou que a maior parte da diversidade permaneceu dentro delas, i.e. BR-105 x BR-106 (G ST = 3,5%) e IG-3 x IG-4 (G ST = 4,0%). A distância genética entre as populações e os sintéticos aumentou em torno de 21%. Houve aumento na divergência genética entre as populações, porém sem comprometer novos procedimentos de seleção.Maize (Zea mays L.) is one of the crops in which the genetic variability has been extensively studied at isoenzymatic loci. The genetic variability of the maize populations BR-105 and BR-106, and the synthetics IG-3 and IG-4, obtained after one cycle of a high-intensity reciprocal recurrent selection (RRS), was investigated at seven isoenzymatic loci. A total of twenty alleles were identified, and most of the private alleles were found in the BR-106 population. One cycle of reciprocal recurrent selection (RRS) caused reductions of 12% in the number of alleles in both populations. Changes in allele frequencies were also observed between populations and synthetics, mainly for the Est 2 locus. Populations presented similar values for the number of alleles per locus, percentage of polymorphic loci, and observed and expected heterozygosities. A decrease of the genetic variation values was observed for the synthetics as a consequence of genetic drift effects and reduction of the effective population sizes. The distribution of the genetic diversity within and between populations revealed that most of the diversity was maintained within them, i.e. BR-105 x BR-106 (G ST = 3.5%) and IG-3 x IG-4 (G ST = 4.0%). The genetic distances between populations and synthetics increased approximately 21%. An increase in the genetic divergence between the populations occurred without limiting new selection procedures

Biologia reprodutiva de etnovariedades de mandioca

The knowledge of the reproductive biology of cassava (Manihot esculenta) is essential for the development of genetic improvement programs and understanding the domestication process. This study evaluates aspects of sexual reproduction, such as floral morphology, pollination ecology, production and viability of pollen grains, apomixis, seed production and seed germination of cassava landraces collected in gardens of "caboclos" and Indians of the Amazon region and São Paulo State, both in Brazil. The aspects of the reproductive biology were studied from field evaluations and collection of flower buds and seeds. The experiments were carried out in Piracicaba, SP. Alteration was verified in the floral morphology of the landrace DG-55, which showed hermaphrodite flowers, and DG-65 and variety Mantiqueira, which presented smaller number of ovules per ovary. Honeybee (Apis mellifera) was the main pollinator of cassava. There was significant variation in the number and viability of pollen grains. The superior anters of the masculine flower presented, significantly, large number of pollen grains. Apomixis was not detected. A larger number of fruits with two or three seeds were detected. However, seeds originating from fruits with a single seed presented higher germination rates. The morphological alterations in the floral structure influenced the seed production and viability. The variation observed in the aspects of the reproductive biology, was probably due to differentiated selective pressure to which the landraces were submitted along the domestication process.O conhecimento da biologia reprodutiva da mandioca é essencial para o desenvolvimento de programas de melhoramento genético e compreensão do processo de domesticação. Este trabalho avalia aspectos que influenciam a reprodução sexuada, tais como morfologia floral, ecologia da polinização, produção e viabilidade dos grãos de pólen, apomixia, produção e germinação de sementes de etnovariedades de mandioca coletadas em roças de caboclos e índios da Região Amazônica e do Estado de São Paulo. Os aspectos da biologia reprodutiva foram estudados a partir de avaliações de campo e coleta de botões florais e sementes. Os experimentos foram realizados em Piracicaba, SP. Constatou-se alteração na morfologia floral da etnovariedade DG-55, a qual possui flores hermafroditas, e DG-65 e variedade Mantiqueira, que apresentaram menor número de óvulos por ovário. A abelha (Apis mellifera) foi o principal polinizador da mandioca. Houve variação significativa no número e viabilidade de grãos de pólen, constatando-se que as anteras do verticilo superior da flor masculina apresentaram, significativamente, maior número de grãos de pólen. Não foi constatada apomixia. Foi detectado maior número de frutos com duas ou três sementes. No entanto, sementes originadas de fruto com semente única apresentaram maior porcentagem de germinação. As alterações morfológicas na estrutura floral influenciaram a produção e viabilidade das sementes. A variação constatada nos aspectos da biologia reprodutiva, provavelmente, ocorreu devido à pressão seletiva diferenciada a que as etnovariedades foram submetidas ao longo do processo de domesticação

Genetic diversity of American wild rice species

Studies on genetic diversity and genetic structure of natural populations are important in order to define strategies for in situ and ex situ conservation actions and for plant pre-breeding programs. Aiming to assess the genetic diversity and genetic structure of three wild American Oryza species with isozyme markers, 14 populations of the diploid O. glumaepatula (AglAgl), 11 populations of the tetraploid O. grandiglumis (CCDD) and five populations of the also tetraploid O. latifolia (CCDD) were studied. They were all originated from Rio Paraguay hydrographic basin and the Amazon. Four enzymes were used and they gave 40 polymorphic bands. The most polymorphic species was O. glumaepatula, followed by O. latifolia and O. grandiglumis. A cluster analysis with the Jaccard similarity coefficient separated the diploid from the two tetraploid species, and also the two tetraploid species. This separation was also evident on a scatter plot from a principal component analysis, suggesting that they should be treated as two separate species, although further studies are necessary to provide support for this affirmative. The AMOVA analyses showed a high intrapopulational variability for O. latifolia (67.6%) and O. grandiglumis (52.2%), when compared to their interpopulational variability (32.4% and 47.8%, respectively), which suggests the hypothesis of a higher degree of outcrossing events within these species. When studying the correlation between the Jaccard dissimilarity coefficient and geographic distances, a spatial genetic structure was observed for O. glumaepatula only. These results are important for defining strategies of both in situ and ex situ conservation.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Baby Cassava: An Alternative Marketing Strategy for Freshly Cut Cassava

There are many procedures for obtaining minimally processed fruits and vegetables, aiming at adding value and maintaining the quality for a longer period. Cassava is a root that adapts to minimum processing technology, because the tissues are more resistant, what helps in obtaining different cut shapes and formats. However, it is a root susceptible to browning and microbiological contamination. In this chapter, methodologies and procedures are described to obtain alternative formats for minimally processed cassava, which was generally denominated “babycassava”, called “babytolete”, “cateto”, and “rubiene”. Besides that, some preharvest and postharvest factors that influence the shape and quality of “babycassava” formats will be addressed. It was verified that preharvest factors could influence the quantitative and qualitative aspects, resulting in browning of the minimally processed root. Some of the factors studied seem to regulate key enzymes in which they mediate oxidative reactions that cause browning, such as polyphenol oxidase and peroxidase, and other enzymes that participate in the reactive oxygen species (ROS) elimination process. In this way, the turning stage of “babycassava” manufacturing removes the parenchyma, minimizing the effect of browning-related enzymes

Isoenzymatic variability in tropical maize populations under reciprocal recurrent selection

Maize (Zea mays L.) is one of the crops in which the genetic variability has been extensively studied at isoenzymatic loci. The genetic variability of the maize populations BR-105 and BR-106, and the synthetics IG-3 and IG-4, obtained after one cycle of a high-intensity reciprocal recurrent selection (RRS), was investigated at seven isoenzymatic loci. A total of twenty alleles were identified, and most of the private alleles were found in the BR-106 population. One cycle of reciprocal recurrent selection (RRS) caused reductions of 12% in the number of alleles in both populations. Changes in allele frequencies were also observed between populations and synthetics, mainly for the Est 2 locus. Populations presented similar values for the number of alleles per locus, percentage of polymorphic loci, and observed and expected heterozygosities. A decrease of the genetic variation values was observed for the synthetics as a consequence of genetic drift effects and reduction of the effective population sizes. The distribution of the genetic diversity within and between populations revealed that most of the diversity was maintained within them, i.e. BR-105 x BR-106 (G ST = 3.5%) and IG-3 x IG-4 (G ST = 4.0%). The genetic distances between populations and synthetics increased approximately 21%. An increase in the genetic divergence between the populations occurred without limiting new selection procedures

Variabilidade genética de etnovariedades de mandioca em regiões geográficas do Brasil Genetic variability of landraces of cassava in geographical regions of Brazil

O manejo empregado nas roças de agricultura autóctone, utilizando etnovariedades de mandioca (Manihot esculenta Crantz), apresenta papel de destaque na conservação in situ dos recursos genéticos. O presente trabalho teve por objetivo analisar a distribuição da variabilidade genética de 141 etnovariedades de mandioca coletadas em roças de diferentes regiões geográficas do Brasil, através de marcadores isoenzimáticos, revelados a partir de eletroforese em gel de amido. Foram avaliados 11 sistemas isoenzimáticos. Dos 15 locos polimórficos analisados a heterozigosidade média observada foi de 0,354. A estimativa coeficiente de diferenciação genética G ST apresentou valor médio de 8,80% da variabilidade genética entre as regiões. Na análise de agrupamento, observou-se a formação de 3 grupos distintos; o primeiro formado pelas roças originadas da Região Amazônica; o segundo constituído pelas roças do Estado de São Paulo; e o terceiro composto pelas roças originadas da Reserva Indígena do Xingu. A maior parte da variabilidade genética das etnovariedades de mandioca revelou-se concentrada dentro das regiões geográficas, confirmando as pressuposições existentes no modelo de dinâmica evolutiva para a espécie.<br>The management practices used in authoctonous agriculture with landraces of cassava (Manihot esculenta Crantz) play an important role in the in situ conservation of genetic resources. The objective of this work was to analyze the genetic variability present in 141 landraces of cassava, collected in gardens of different geographical regions of Brazil using isozyme techniques visualized by starch gel electrophoresis. Eleven enzymatic systems were analised. Of the 15 polymorphic loci evaluated the observed mean heterozigosity was 0.354. G STestimates presented a value of 8.80% for the genetic variability between regions. In cluster analysis, three distinct groups were observed: the first group was formed by the gardens of the Amazon; the second group consisted of gardens of São Paulo State; and the third group was formed by the gardens of the Xingu region. Most of the genetic variability of cassava landraces was restricted within the geographical regions, which confirmed the evolutionary dynamic model for this species