Marcia Flores da Silva

Estimating the effects of population size and type on the accuracy of genetic maps

Based on simulation studies, it was shown that the type and size of experimental populations can exert an influence on the accuracy of genetic maps. A hypothetical genome map (one chromosome with nine equidistant molecular markers) was generated for the following population types: F2 with dominant and co-dominant markers, backcrossing, recombinant inbred lines (RIL) and double-haploid. The population sizes were 50, 100, 150, 200, 500 and 1000 individuals and 100 simulations were made for each population. The inaccuracies of the populations with the lowest number of individuals were shown by inversions in the order of the markers and the establishment of more than one linkage group in up to 38% of the simulations, depending on the population type. Stress and variance values of the distances between adjacent markers were significantly reduced with the increased size of the population. More accurate maps were obtained for the co-dominant F2 and RIL whereas the maps for the dominant F2 population were less accurate. The higher the number of individuals, the more precise was the map. In all populations, a total of 200 individuals were considered as being sufficient for the construction of reasonably accurate genetic maps. Although this paper deals with plant populations this approach is equally applicable to other organisms.

Parâmetros genéticos em café Conilon

O objetivo deste trabalho foi avaliar a produtividade e obter as estimativas de parâmetros geneticos e nao geneticos de 40 materiais geneticos do programa de melhoramento genetico de cafe Conilon do Incaper, no Estado do Espirito Santo. Foram analisados dados de dois experimentos, nos municipios de Marilândia e Sooretama, ES, nas safras de 1996, 1997, 1998, 1999, 2000, 2001 e 2002, em que se avaliaram 16 caracteristicas. Realizou-se, inicialmente, a analise de variância individual, por local em cada ano, com base na media de parcelas, em blocos ao acaso. Posteriormente foi feita a analise de variância conjunta. Os genotipos apresentaram grande variabilidade genetica para a maioria das caracteristicas avaliadas. Os elevados coeficientes de determinacao genotipico e coeficientes de variacao geneticos, associados as altas produtividades e a variabilidade genetica indicam a possibilidade de obtencao de exitos em programas de melhoramento genetico para diferentes caracteristicas avaliadas nos dois municipios.

Repetibilidade e número de colheitas para seleção de clones de cana-de-açúcar

This work aimed at the establishment of the repeatability coefficients (r), determination of the predictability degree (R2) and the needed measurement numbers for tons of cane per hectare, percentage of pol (sucrose) in the juice of cane and tons of pol in the juice of cane per hectare in sugarcane genotypes. A randomized block experimental design, with three replicates in four experiments and four replicates in the other experiments was used. The repeatability estimates were obtained by the statistical methods: anova; main components based on correlation matrix; and structural analysis (correlation, average r). The estimates of the repeatability coefficients showed values with very similar magnitude. The general average repeatability for those three traits was above 0.60, therefore showing regularity in the genotype performance at several measurements (cuts) and reliability in the genotype discrimination that was higher than 87%. The results showed that for those three traits there is a need for the use of, at least, three cuts so that the selection can be accomplished with predictability of a real value above 80% for the genotype.

Validação de marcadores microssatélites para a seleção assistida de resistência de soja ao nematóide-de-cisto raças 3 e 14

O objetivo deste trabalho foi validar marcadores microssatelites associados a resistencia as racas 3 e 14 do nematoide-de-cisto (Heterodera glycines Ichinohe) da soja (Glycine max L.), para serem utilizados em programas de selecao assistida por marcadores moleculares (SAM). Microssatelites dos grupos de ligacao A2, D2 e G da soja foram testados em duas populacoes, e suas eficiencias de selecao foram determinadas. As populacoes foram 65 familias F2:3, do cruzamento Msoy8001 (resistente) x Conquista (suscetivel), e 66 familias F2:3, do cruzamento S5995 (resistente) x Renascenca (suscetivel), avaliadas para a resistencia as racas 3 e 14, respectivamente. Familias com indice de femeas de ate 30% foram consideradas moderadamente resistentes. Marcadores dos grupos de ligacao A2 e G apresentaram associacao com a resistencia a raca 3. Os marcadores Satt309 e GMENOD2B explicaram a maior proporcao da variância fenotipica nos diferentes grupos. As combinacoes Satt309+GMENOD2B e Satt309+Satt187 apresentaram eficiencia de selecao de 100%. A resistencia a raca 14 foi associada com marcadores do grupo de ligacao G, e a eficiencia de selecao da combinacao Satt309+Satt356 foi de 100%. Os diferenciais de selecao fenotipica e de selecao assistida mostraram que os dois tipos de selecao podem proporcionar ganhos similares.

Inheritance of resistance to soybean cyst nematode races 3 and 14 in soybean RIL and F2 populations

The objective of this work was to evaluate the soybean inheritance of resistance to cyst nematode races 3 and 14. The following populations where evaluated: one population of recombinant inbred lines (RILs) [Hartwig (resistant) x Y23 (susceptible line)] for races 3, 14 and 9; one population of families F2:3 [M-SOY 8001 (resistant) x MB/BR 46 - Conquista (susceptible)] for race 3; and one population of families F2:3 [(S5995 (resistant) x BRSMG Renascenca (susceptible)] for race 14. In RIL populations, four epistatic genes were identified which conditioned resistance to race 14, and three epistatic ones for resistance to races 3 and 9. The lack of one gene provided moderate resistance under all situations. The highest number of genes for resistance to race 14 points out that genes responsible for lower effects might be involved. In population F2:3 from M-SOY 8001 x MB/BR 46 - Conquista, one recessive gene for moderate resistance and two recessive genes complete resistance to race 3 were identified. Two recessive genes conditioning moderate resistance to race 14 were identified in population F2:3 from the crossing S5995 x BRSMG Renascenca. These results will be useful in designing crossings, involving these parentals, with higher possibility to accumulating genes that provide resistance to several SCN races.