Roland Vencovsky

Genetic diversity and natural population structure of cacao (Theobroma cacao L.) from the Brazilian Amazon evaluated by microsatellite markers

A sample of 94 accessions of Theobroma cacao L. (cacao), representing four populations from the Brazilian Amazon (Acre, Rondônia, lower Amazon and upper Amazon) were analyzed using microsatellite markers to assess the genetic diversity and the natural population structure. From the 19 microsatellite loci tested, 11 amplified scorable products, revealing a total of 49 alleles, including two monomorphic loci. The Brazilian upper Amazon population contained the largest genetic diversity, with the most polymorphic loci, the highest observed heterozygosity; and the majority of rare alleles, thereby this region might be considered part of the center of diversity of the species. The observed heterozygosity for all the Brazilian populations (Ho = 0.347) was comparable with values reported for other similar upper Amazon Forastero cacao populations, with the Acre and Rondônia displaying the lowest values. The lower Amazon population, traditionally defined as highly homozygous, presented an unexpectedly high observed heterozygosity (Ho = 0.372), disclosing rare and distinct alleles, with large identity with the upper Amazon population. It was hypothesized that part of the lower Amazon population might derive from successive natural or intentional introduction of planting material from other provenances, mainly upper Amazon. Most of the loci exhibited a lower observed heterozygosity than expected, suggesting that self-pollination might be more common than usually assumed in cacao, but excess of homozygotes might also derive from sub-grouping (Wahlund effect) or from sampling related individuals. Most of the gene diversity was found to occur within groups, with small differentiation between the four Brazilian Amazon populations, typical of species with high gene flow.

Genetic diversity of Musa diploid and triploid accessions from the Brazilian banana breeding program estimated by microsatellite markers

Banana (Musa spp.) is one of the most consumed fruits worldwide. Production is based mainly on triploid cultivars, and most genetic improvement programs aim to generate tetraploid hybrids obtained from the crossing of established triploid cultivars with a diploid parent genotype, improved or wild, exhibiting the trait of interest, normally resistance to biotic factors. Microsatellites were used to investigate the genetic variability and relationships between 58 Musa genotypes, including 49 diploids and nine triploid cultivars maintained at the Musa germplasm collection of the Brazilian dessert banana breeding program. Thirty-three primer pairs developed for banana were tested, and nine amplified reproducible and discrete fragments, producing a total of 115 alleles. The average number of alleles amplified per primer was 12.8, ranging from 10 to 15. The diploid genotypes presented the largest genetic variability, demonstrated by the large number of alleles detected, and the low similarity between the clones. The phenetic analysis clustered the triploid cultivars in a separated group, with the exception of the ‘Nanica’ and ‘Gros Michel’ cultivars, which showed high similarity with the diploid cultivar ‘Mambee Thu’. It was not possible to separate the wild diploid genotypes from the cultivated ones, indicating a common origin of these genotypes. A high proportion of duplicated alleles and/or loci was observed for diploid and triploid genotypes. The information gathered about the similarity between diploid and triploid accessions will help to define potential crosses to maximize the recovery of the typical fruit qualities required in Brazil (AAB, Pome and Silk dessert banana).

Estrutura genética e fluxo gênico em populações naturais de cagaita

Este trabalho teve por objetivo o estudo da variabilidade genetica em 10 populacoes de cagaiteiras (Eugenia dysenterica), da regiao Sudeste do Estado de Goias. Foram identificados 54 locos marcadores RAPD, para a caracterizacao da variabilidade genetica, avaliada por meio da analise da variância molecular (AMOVA). Foi verificado que 27,03% da variabilidade genetica esta entre populacoes, e 72,97% dentro de populacoes, indices obtidos a partir do valor de fST igual a 0,2703. Foi estimado o coeficiente de correlacao de Pearson (r) entre a matriz de distâncias geneticas (1 - indice de similaridade de Jaccard) e de distâncias geograficas, tendo sido encontrada forte correlacao positiva. Os resultados sugerem que essas populacoes estao se diferenciando por um processo estocastico havendo fluxo restrito dependente da distribuicao geografica.

Genetic gain in the breeding program of common beans at IAC from 1989 to 2007

The goal of the present work was to evaluate the genetic gain obtained in grain yield for the common bean genotypes from 1989 until 2007, at the Instituto Agronomico de Campinas, in the state of Sao Paulo. Genetic gain has been separated into two research periods; the first, from 1989 to 1996, and the second, from 1997 to 2007. In the first period, a genetic gain of 1.07 % per year was obtained, whereas for the second period, the gain was zero. However, the mean yield of the evaluated lines was approximately 1000 kg ha-1 superior to the figures obtained in the first period. The main cause for the absence of genetic gain in the second period is that the focus of the breeding program was changed to grain quality. The individualized analysis of the genotypes with carioca grains in the second period indicated the lack of genetic gain during the investigated period.

Correlações e análise de trilha de caracteres tecnológicos e a produtividade de fibra de algodão

O objetivo deste trabalho foi avaliar as relacoes entre os caracteres tecnologicos (variaveis independentes explicativas) e a produtividade de fibra do algodao (variavel dependente) e identificar seus efeitos diretos e indiretos pela analise de trilha. Os caracteres tecnologicos foram: finura, resistencia, comprimento, uniformidade de comprimento, alongamento e indice de fiabilidade do fio. Avaliaram-se 12 cultivares de algodoeiro herbaceo, no Estado do Mato Grosso, no ano agricola 2000/2001. Estimaram-se as correlacoes, e fez-se a analise de trilha pelo metodo proposto por Wright. O carater finura apresenta o maior efeito direto sobre a produtividade da fibra. A resistencia, o comprimento e o alongamento tem efeito secundario. A uniformidade de comprimento e a fiabilidade apresentaram efeito indireto via finura. Um esquema de selecao restrito e necessario, para se eliminarem os efeitos indiretos negativos do indice de fiabilidade sobre a finura.

Family by environment interaction in sugarcane: effect on the expected response to selection

Thirty three families obtained in biparental and polycrosses were evaluated at two sites in the State of Sao Paulo - Brazil, Piracicaba and Jau, in order to quantify the Family x Environment (FE) interaction and its effect on the expected response to selection. Stalk height, stalk diameter, number of stalks, sugar content (Brix), cane yield per hectare (TCH) and sugar yield per hectare (TB) were evaluated. Results indicate a significant FE interaction (p<0.01) for all traits measured. Although always less than the family variance (), the FE interaction variance () was from 12,3% to 75,7% of the family variance () for stalk diameter and TBH, respectively. The decomposition of the FE interaction variance, in genotypic and phenotypic components, made evident its complex nature, making it difficult to select families adapted to both sites. Simulated responses to selection (SRf) showed that indirect selection (selection in one environment and expected response in another) has very low efficiency and was in some cases, such as TBH, negative. Selection based on the mean of both sites presented gains, however these gains would have been 62% and 43% greater (for Piracicaba and Jau, respectively) had the selection and response been made on the same site.

Capacidade de combinação em sete populações de melancia

Este trabalho teve como objetivo estimar as capacidades geral (CGC) e especifica (CEC) de combinacao e os efeitos reciprocos (ER) em relacao a precocidade, componentes de producao e caracteristicas do fruto em sete populacoes de melancia. As populacoes foram intercruzadas em dialelo, incluindo os reciprocos. Todas as variaveis avaliadas, com excecao do numero de frutos por planta, apresentaram efeitos da CGC, CEC e ER significativos. Efeitos genicos aditivos foram importantes em relacao ao numero e peso de frutos por planta, assim como em relacao a cor, espessura e teor de solidos soluveis da polpa. Quanto ao numero de dias para o aparecimento da primeira flor feminina e numero de sementes por fruto, ocorreu predominância de efeitos genicos nao-aditivos. Foram identificadas algumas populacoes e algumas combinacoes hibridas superiores, que podem ser exploradas em programas de melhoramento. As populacoes tradicionais P14 e B9, coletadas no Nordeste do Brasil, sao promissoras para serem empregadas em programas que visem melhorar o numero e o peso dos frutos, ao passo que a M7 e promissora em relacao a precocidade. As variedades comerciais Charleston Gray e Crimson Sweet poderao ser empregadas para melhorar o teor de acucar e a cor da polpa.

Paternity analysis reveals significant isolation and near neighbor pollen dispersal in small Cariniana legalis Mart. Kuntze populations in the Brazilian Atlantic Forest

Abstract Throughout the world, large trees are increasingly rare. Cariniana legalis is the tallest tree species of the Brazilian Atlantic Forest, reaching up to 60 m in height. Due to extensive deforestation of the Atlantic Forest, remnant C. legalis populations are small and spatially isolated, requiring the development of strategies for their conservation. For in situ and ex situ genetic conservation to be effective, it is important to understand the levels and patterns of spatial genetic structure (SGS), and gene flow. We investigated SGS and pollen flow in three small, physically isolated C. legalis stands using microsatellite loci. We measured, mapped, and sampled all C. legalis trees in the three stands: 65 trees from Ibicatu population, 22 trees from MGI, and 4 trees from MGII. We also collected and genotyped 600 seeds from Ibicatu, 250 seeds from MGI, and 200 seeds from MGII. Significant SGS was detected in Ibicatu up to 150 m, but substantial levels of external pollen flow were also detected in Ibicatu (8%), although not in MGI (0.4%) or MGII (0%). Selfing was highest in MGII (18%), the smallest group of trees, compared to MGI (6.4%) and Ibicatu (6%). In MGI and MGII, there was a strong pattern of mating among near‐neighbors. Seed collection strategies for breeding, in situ and ex situ conservation and ecological restoration, must ensure collection from seed trees located at distances greater than 350 m and from several forest fragments.

Genetic diversity of Couratari multiflora and Couratari guianensis (Lecythidaceae): consequences of two types of rarity in central Amazonia

We quantified the within-population genetic variation of Couratari multiflora and C. guianensis, two tree species found in terra firme forests of central Amazonia. Both species have some ecological features in common, but they differ in population abundance across their geographic ranges. While C. multiflora has been found only in low-density populations in all sites studied to date, C. guianensis is relatively common in some sites and very scarce in others. In a 400-ha plot, we found 41 and 29 adults of C. multiflora and C. guianensis, respectively. Twenty-two saplings of C. guianensis and 103 seedlings of C. multiflora were also examined. The mean expected heterozygosities (Hem) of seedlings and adults of C. multiflora were 0.431 and 0.436, and the mean fixation indices (Fm), 0.114 and 0.176, respectively. For C. guianensis, saplings and adults presented Hem equal to 0.425 and 0.429, and the Fm were 0.393 and 0.527, respectively. These low-density populations of two congeneric species did not differ in terms of genetic diversity, but rather they differed in terms of mean observed heterozygosity (Hom), and therefore Fm. The species with variable population density had lower Hom and greater Fm relative to the species that is always found in low-density.

Estimadores de componentes de variância em delineamento de blocos aumentados com tratamentos novos de uma ou mais populações

This work compares by simulation estimates of variance components produced by the ANOVA (analysis of variance), ML (maximum likelihood), REML (restricted maximum likelihood), and MIVQUE(0) (minimum variance quadratic unbiased estimator) methods for augmented block design with additional treatments (progenies) stemming from one or more origins (crosses). Results showed the superiority of the MIVQUE(0) estimation. The ANOVA method, although unbiased, showed estimates with lower precision. The ML and REML methods produced downwards biased estimates for error variance (), and upwards biased estimates for genotypic variances (), particularly the ML method. Biases for the REML estimation became negligible when progenies were derived from a single cross, and experiments were of larger size with ratios />0.5. This method, however, provided the worst estimates for genotypic variances when progenies were derived from several crosses and the experiments were of small size (n<120 observations).