Ronan Xavier Corrêa

RAPD markers linked to a block of genes conferring rust resistance to the common bean

Abstract Rust, caused by the fungus Uromyces appendiculatus , may cause a significant loss to common bean ( Phaseolus vulgaris L.) yield.RAPD markers tightly linked to the resistance genes may be used in breeding programs to aid the development of rust-resistant b eancultivars. In this sense, the objective of the present work was to identify RAPD markers linked to a rust resistance gene block present inthe cultivar Ouro Negro. Two hundred and fourteen F 2 individuals from a cross between the resistant cultivar Ouro Negro and thesusceptible cultivar US Pinto 111 were inoculated with a mixture of eight races of U. appendiculatus . The segregation ratio obtainedsuggested that resistance is monogenic and dominant. Bulked segregant analysis was used in conjunction with the RAPD technique tosearch for markers linked to rust resistance genes. Two molecular markers flanking the rust resistance gene block were identifi ed, one at5.8 ± 1.6 cM (OX11 630 ) and the other at 7.7 ± 1.7 cM (OF10

Mapeamento de genes de resistência do feijoeiro à ferrugem, antracnose e mancha-angular usando marcadores RAPD

Molecular markers were used to study the organization of rust, anthracnose and angular leaf spot resistance genes in common bean (Phaseolus vulgaris) Ouro Negro cultivar. A segregant population of 154 recombinant inbred lines (RIL´s) from the crossing between Ouro Negro and Ruda cultivars was inoculated under controlled conditions with seven races of Uromyces appendiculatus, three of Colletotrichum lindemuthianum and four of Phaeoisariopsis griseola. DNA samples of each RIL were amplified by polymerase chain reaction using 70 decamer primers. Segregation analysis of rust, anthracnose and angular leaf spot resistance suggested specific resistance inheritance to each physiologic race. Genetic linkage analysis revealed the grouping of different rust and anthracnose resistance genes in the same linkage group. Angular leaf spot resistance genes also were mapped together, but in another linkage group. The utility of RAPD markers linked to common bean resistance genes, previously identified in the literature, was restricted. Only five out of 38 molecular markers tested were validated on the RIL´s population as linked to rust and anthracnose resistance genes. Three new molecular markers (OBA16669 and OAB16583 to 10.4 cM in coupling and OAD93210 to 13.9 cM in repulsion) were identified that are linked to to the angular leaf spot resistance gene block in Ouro Negro cultivar.

Genetic distances in soybean based on RAPD markers

Four methods were applied to determine pairwise genetic distances among five soybean genotypes which are potential genitors for a mapping population. Additionally, individual plants from the most divergent pair of genotypes were evaluated by the RAPD technique to determine their degree of homozygosity. Genetic distances based on RAPD data were calculated by the modified Rogers distance, and also by the following arithmetical complements of similarity: simple match, Nei and Li, and Gower. These genetic distances were similar, presenting a correlation coefficient ranging from 0.99 to 1.00. In all four methods lines UFV 91-717 and Ichigowase were the most divergent ones (4.53 to 21.43%). DNA samples from five plants from each of the two most divergent genotypes were amplified with 28 different primers. Among the amplified products, only five were polymorphic in each group (2.10%), demonstrating their high intragroup degree of homozygosity. These homozygosity were maintained when DNA samples from 12 plants from each of the two most divergent genotypes were amplified. These parameters were extremely useful for the confirmation of the chosen pair of genitors to generate a mapping population.

Herança da resistência à mancha-angular do feijoeiro e identificação de marcadores moleculares flanqueando o loco de resistência

Angular leaf spot, caused by the fungus Phaeoisariopsis griseola, is one of the most important diseases affecting the common bean (Phaseolus vulgaris). Molecular markers linked to a few resistance genes have been identified, however, they are insufficient to monitor all the different sources of resistance. For this reason, in this work we aimed at studying the inheritance of resistance to P. griseola pathotypes 63.39 and 31.23 in populations derived from Ouro Negro (ON) and US Pinto 111 (PT), and identifying molecular markers linked to the resistance loci present in these two cultivars. The genitor ON, F1 (ON x PT) and ¾ of the F2 population were resistant to pathotype 63.39. The genitor PT and ¼ of F2 plants were susceptible. When pathotype 31.23 was used, the genitor PT and ¼ of F2:3 families were resistant and all the other families were susceptible indicating that resistance of ON to pathotype 63.39 is conferred by a dominant gene while resistance of PT to pathotype 31.23 is conferred by a recessive gene. These two loci segregated independently. DNA samples extracted from F2 plants were amplified by the Random Amplified Polymorphic DNA (RAPD) technique and analyzed through the bulk segregant strategy. Two markers, OPM02460C and OPAA19600C, located at 5.3 and 10 centimorgans (cM) of the resistance locus, respectively, were identified in ON. These markers flank the resistance locus and their selection efficiency was 97.4% when used simultaneously. No markers were identified linked to the resistance locus present in PT.

Caracterização de uma população de cacaueiro para mapeamento de genes de resistência à vassoura-de-bruxa e podridão-parda

O cacaueiro (Theobroma cacao) e alvo de diversas enfermidades, sendo que a podridao-parda, causada por Phytophthora spp. e a principal delas mundialmente. Entretanto, no Brasil, a vassoura-de-bruxa causada por Crinipellis perniciosa, e a mais devastadora. A busca de fontes de resistencia as doencas e a etapa basica para programas de melhoramento genetico e, nesse sentido, este estudo objetivou caracterizar quantitativamente uma progenie oriunda do cruzamento entre os clones SIC-864 e CCN-51, dois genotipos contrastantes para diversas caracteristicas, inclusive para resistencia a vassoura-de-bruxa e podridao-parda. Foram avaliados em condicoes de campo o numero medio de frutos por planta por ano, porcentagem de frutos sadios, porcentagem de frutos com vassoura-de-bruxa, porcentagem de frutos com podridao-parda, numero medio de vassouras vegetativas por planta por ano e numero medio de vassouras de almofada floral por planta por ano, durante um periodo de quatro anos. As estatisticas descritivas da produtividade e da resistencia a doencas foram calculadas considerando os valores maximo, medio e minimo, o desvio padrao, o coeficiente de variacao, e a distribuicao da frequencia. O coeficiente de repetibilidade foi calculado para estimar a acuracia da variacao fenotipica por efeitos ambientais pelos metodos da analise de variância, componentes principais e analise estrutural. Foi demonstrado o carater segregante dessa progenie para resistencia a vassoura-de-bruxa e a podridao-parda e para outras caracteristicas, mostrando a utilidade da populacao para estudos de mapeamento genetico utilizando marcadores moleculares, visando identificar genes de resistencia e quantitative trait loci (QTLs) dissimilares dos encontrados no clone Scavina-6, tradicionalmente usado em programas de melhoramento genetico do cacaueiro.

Caracterização de linhagens endogâmicas recombinantes e mapeamento de locos de características quantitativas associados a ciclo e produtividade do feijoeiro-comum

O objetivo deste trabalho foi caracterizar 154 linhagens endogâmicas recombinantes por meio da avaliacao de caracteristicas quantitativas, morfologicas, moleculares e de resistencia a doencas e mapear locos de caracteristicas quantitativas associados a ciclo e produtividade do feijoeiro-comum. Adotando o valor do limite de deteccao (LOD) de 4,0 e uma frequencia maxima de recombinacao de 0,40, foram mapeados 43 marcadores em nove grupos de ligacao cobrindo uma distância de recombinacao total de 247,8 cM. A distância entre marcadores adjacentes variou entre 0 e 28 cM, com media de 7,3 cM. Os grupos de ligacao variaram em tamanho de 2,3 a 61,2 cM. Os genes de resistencia a ferrugem e a antracnose ficaram localizados no mesmo grupo de ligacao. Foram mapeados locos associados as oito caracteristicas quantitativas estudadas, e a explicacao da variância fenotipica pelos marcadores variou de 14,03% a 40,14%. Os resultados encontrados lancam bases para o desenvolvimento de mapas especificos saturados e de utilidade em programas de melhoramento do feijoeiro-comum.

Diversidade genética de Chenopodium ambrosioides da região cacaueira da Bahia com base em marcadores RAPD

Chenopodium ambrosioides L. is known in many parts of Brazil for its medicinal properties, mainly used to control intestinal worms. Its genetic diversity is little studied. The objective of this work was to evaluate the genetic variability of 16xa0accessions of C.xa0ambrosioides from the cocoa region of Bahia State, Brazil, by the RAPD technique (Random Amplified Polymorphic DNA). Only 6.9% of the 216xa0amplified RAPD bands were polymorphic and the pattern of dispersion of individuals showed no clustering related to sample site. Therefore, there is low variability among accessions and it is distributed among the accessions from the entire sampled region.

Evaluation of the genetic diversity of a set of parents of Eucalyptus spp. by using microsatellite markers to direct matings

Background To obtain genetically superior cultivars in a breeding program, methods and procedures are necessary to allow the identification of selected individuals over several cycles of selection while at the same time maintain broad genetic base of the breeding populations. This is crucial to guarantee continuous genetic gains along the program. The establishment of efficient breeding strategies depends on methods and analytical tools. The assessment of genetic diversity with molecular markers of parents used in mating designs could aid optimizing the recombination phase. Microsatellites provide good information content and require small amounts of DNA and may be transferable between species of the same genus. In this study we evaluated the genetic diversity in a set of Eucalyptus parent trees and indicated those to be preferentially crossed in a recombination process to potentially maximize variation in the offspring for individual selection of clones.