No abstract

It takes approximately 14 yr to produce a new rice (Oryza sativa L.) variety, that is, from initial hybridization to its commercial release. Currently, new varieties are identified based on morphological descriptors, which have been efficient over time. However, due to the main constraints on seed type impose to other breeding objectives and the pressure of continuous release of varieties, high degree of parentage, and genetic and morphological uniformity has been observed in the breeding populations. The objectives of this study were: to determine the genetic variability of Chilean and foreign commercial rice varieties, and determine, identify, and certify the genetic relationships among varieties, using simple sequence repeat (SSR) markers. A total of 16 commercial varieties, some of them closely related, were included in the study, which were genetically analyzed using 54 microsatellites. The 54 microsatellite loci allowed the discrimination among the 16 varieties. The number of alleles ranged between 2 and 8 with a mean of 3.54 alleles per locus, while the polymorphism information content (PIC) presented a mean of 0.44. The genetic distance and diversity parameters between pairs of varieties indicate a limited diversity among these genotypes. The cluster analysis indicated that varieties were grouped according to their grain type and pedigree. Results demonstrate that the identification and certification of varieties using microsatellite markers could be a good complement to existing agro-morphological data when varieties are closed related.

Rice Breeding Program (RBP) of the Instituto de Investigaciones Agropecuarias (INIA) at Chillán, Chile, has a rice (Oryza sativa L.) germplasm collection that consists of 1200 accessions, mainly temperate japonica rice accessions, well adapted to the local conditions. Most of the new introduced accessions adapt very poorly to Chilean agroecological conditions because of requirements of long days and cold tolerance. The objectives of this study were to use microsatellites to evaluate level of polymorphism of a representative sample of this collection and determine its genetic diversity and relationships with cultivated germplasm from different geographical origin. A total of 249 genotypes were analyzed with 30 selected polymorphic microsatellites. Total number of alleles scored across 249 genotypes was 183 with an overall mean of 6.1 alleles per locus, ranging 2-14. The mean major allele (most common) frequency was 0.61 and mean minor allele frequency was 0.028. The overall mean gene diversity across 30 SSR loci was 0.52. Mean heterozygosity was 0.01, and mean polymorphism information content (PIC) value was 0.47. The accessions were organized by structure analysis into three main groups and revealed a fairly consistent genetic relationship with dendrogram and Principal Coordinates Analysis (PCoA). The temperate japonica accessions can be further subdivided into three subpopulations where long and short Chilean varieties were grouped into different clusters. The three populations showed different level of admixture, admixture probably due to previous breeding work through years. Results indicate that polymorphism levels of Chilean rice temperate japonica collection has similar magnitude as temperate japonica germplasm reported in the literature.