ABSTRACT
In Venezuela, pedigree analyses indicate that the rice varieties currently under cultivation are closely related. Effective breeding programs, based on knowledge of the genetic diversity of cultivars, are needed to broaden the genetic bases of rice germplasm in the country. In this study, we used a set of 48 simple-sequence-repeat (SSR) markers to assess the genetic diversity of 11 Venezuelan rice cultivars, released by the National Rice Breeding Program between 1978 and 2007. A total of 203 alleles were detected, the number of alleles (NA) per marker ranged from 2 to 9, with an average of 4.23. The average genic diversity (H) over all SSR loci for the 18 genotypes was 0.524, ranging from 0.105 to 0.815. Positive correlations were found between H at each locus, NA, the allele size range and the maximum number of repeats. Venezuelan cultivars showed lower H (mean = 0.37) and NA (total = 124, mean = 2.58) than the whole sample. UPGMA-cluster-analysis based on genetic distance coefficients clearly separated all the genotypes, and showed that the Venezuelan rice varieties are closely related. Molecular identification of 7 Venezuelan cultivars could be done with 9 primers pairs which produced 10 genotype-specific-alleles. Although the genetic diversity was low, SSRs proved to be an efficient tool in assessing the genetic diversity of rice genotypes. Implications of the low genetic diversity detected and relatedness of Venezuelan cultivars are discussed.
Subject(s)
Genetic Markers , Oryza/genetics , Alleles , Venezuela , Genetic Variation/geneticsABSTRACT
Microsatellite polymorphism was studied in a sample of 39 traditional rice (Oryza sativa L.) varieties and 11 improved varieties widely planted in Cuba. The study was aimed at assessing the extent of genetic variation in traditional and improved varieties and to establish their genetic relationship for breeding purposes. Heterozygosity was analyzed at each microsatellite loci and for each genotype using 10 microsatellite primer pairs. Between varieties genetic relationship was estimated. The number of alleles per microsatellite loci was 4 to 8, averaging 6.6 alleles per locus. Higher heterozygosity (H) was found in traditional varieties (H TV = 0.72) than in improved varieties (H IV = 0.42), and 68 percent of the total microsatellite alleles were found exclusively in the traditional varieties. Genetic diversity, represented by cluster analysis, indicated three different genetic groups based on their origin. Genetic relationship estimates based on the proportion of microsatellite loci with shared alleles indicated that the majority of traditional varieties were poorly related to the improved varieties. We also discuss the more efficient use of the available genetic diversity in future programs involving genetic crosses.
ABSTRACT
La bacteriosis vascular de la yuca es una destructiva enfermedad en Sur América y África, causada por la bacteria Xanthomonas axonopodis pv. manihotis (Xam). Produce pérdidas entre el 12 por cien y 100 por cien de los cultivos. Algunos estudios se han realizado a nivel bioquímico y citoquímico para conocer las respuestas de defensa de la yuca a Xam; sin embargo,las bases moleculares de los mecanismos de defensa no han sido aún caracterizadas. Con el propósito de identificar genes diferencialmente expresados durante la respuesta de la planta al patógeno, se ha construido una librería sustractiva, usando el método de Sustracción Diferencial en Cadena (DSC), con 1536 clones de dos variedades resistentes(MBRA 685 y SG 107-35). De esta librería fueron seleccionados al azar 110 clones para ser secuenciados y realizar búsquedas de similitud en bases de datos públicas. El análisis de secuencia mostró 14 clones con similitud a genes previamente reportados como involucrados en procesos de defensa en plantas, 70 clones con similitud a genes de plantas sin función conocida o que no presentaron similitud, representando nuevos genes potencialmente involucrados en las respuestas de defensa de la yuca. Finalmente fueron construidos microarreglos de ADNc, usando los clones seleccionados de las librerías sustractivas para confirmar su expresión diferencial durante el desarrollo dela infección.