Genetic structure and mating type analysis of the Pyricularia oryzae population causing widespread epidemics in southern Brazil.

Blast is a major disease of rice in Brazil, the largest rice-producing country outside Asia. This study aimed to assess the genetic structure and mating-type frequency in a contemporary Pyricularia oryzae population, which caused widespread epidemics during the 2012/13 season in the Brazilian lowland subtropical region. Symptomatic leaves and panicles were sampled at flooded rice fields in the states of Rio Grande do Sul (RS, 34 fields) and Santa Catarina (SC, 21 fields). The polymorphism at ten simple sequence repeats (SSR or microsatellite) loci and the presence of MAT1-1 or MAT1-2 idiomorphs were assessed in a population comprised of 187 isolates. Only the MAT1-2 idiomorph was found and 162 genotypes were identified by the SSR analysis. A discriminant analysis of principal components (DAPC) of SSR data resolved four genetic groups, which were strongly associated with the cultivar of origin of the isolates. There was high level of genotypic diversity and moderate level of gene diversity regardless whether isolates were grouped in subpopulations based on geographic region, cultivar host or cultivar within region. While regional subpopulations were weakly differentiated, high genetic differentiation was found among subpopulations comprised of isolates from different cultivars. The data suggest that the rice blast pathogen population in southern Brazil is comprised of clonal lineages that are adapting to specific cultivar hosts. Farmers should avoid the use of susceptible cultivars over large areas and breeders should focus at enlarging the genetic basis of new cultivars.

Genetic diversity of the forage peanut in the Jequitinhonha, São Francisco, and Paranã River valleys of Brazil.

Arachis pintoi and A. repens are legumes with a high forage value that are used to feed ruminants in consortium systems. Not only do they increase the persistence and quality of pastures, they are also used for ornamental and green cover. The objective of this study was to analyze microsatellite markers in order to access the genetic diversity of 65 forage peanut germplasm accessions in the section Caulorrhizae of the genus Arachis in the Jequitinhonha, São Francisco and Paranã River valleys of Brazil. Fifty-seven accessions of A. pintoi and eight of A. repens were analyzed using 17 microsatellites, and the observed heterozygosity (HO), expected heterozygosity (HE), number of alleles per locus, discriminatory power, and polymorphism information content were all estimated. Ten loci (58.8%) were polymorphic, and 125 alleles were found in total. The HE ranged from 0.30 to 0.94, and HO values ranged from 0.03 to 0.88. By using Bayesian analysis, the accessions were genetically differentiated into three gene pools. Neither the unweighted pair group method with arithmetic mean nor a neighbor-joining analysis clustered samples into species, origin, or collection area. These results reveal a very weak genetic structure that does not form defined clusters, and that there is a high degree of similarity between the two species.

Genetic parameters and mapping quantitative trait loci associated with tibia traits in broilers.

Abstract: Selection among broilers for performance traits is resulting in locomotion problems and bone disorders, once skeletal structure is not strong enough to support body weight in broilers with high growth rates. In this study, genetic parameters were estimated for body weight at 42 days of age (BW42), and tibia traits (length, width, and weight) in a population of broiler chickens. Quantitative trait loci (QTL) were identified for tibia traits to expand our knowledge of the genetic architecture of the broiler population. Genetic correlations ranged from 0.56 +/- 0.18 (between tibia length and BW42) to 0.89 +/- 0.06 (between tibia width and weight), suggesting that these traits are either controlled by pleiotropic genes or by genes that are in linkage disequilibrium. For QTL mapping, the genome was scanned with 127 microsatellites, representing a coverage of 2630 cM. Eight QTL were mapped on Gallus gallus chromosomes (GGA): GGA1, GGA4, GGA6, GGA13, and GGA24. The QTL regions for tibia length and weight were mapped on GGA1, between LEI0079 and MCW145 markers. The gene DACH1 is located in this region; this gene acts to form the apical ectodermal ridge, responsible for limb development. Body weight at 42 days of age was included in the model as a covariate for selection effect of bone traits. Two QTL were found for tibia weight on GGA2 and GGA4, and one for tibia width on GGA3. Information originating from these QTL will assist in the search for candidate genes for these bone traits in future studies.