Constituição genômica e relações entre espécies de Urochloa P. Beauv.

Abstract

The genus Urochloa P. Beauv. (sin. Brachiaria (Trin.) Griseb.) comprises species of great economic relevance as forages. The genomic constitution for the alotetraploid species U. brizantha (cv. Marandu) and U. decumbens (cv. Basilisk) and the diploid U. ruziziensis was previously proposed as BBB¹B¹, B¹B¹B²B² and B²B², respectively. Evidence indicates U. ruziziensis as the ancestral donor of genome B² in U. decumbens alotetraploidy, but the origin of the genomes B and B¹ is still unknown. There are diploid accessions of U. brizantha e U. decumbens that may be potential ancestors of the tetraploids. The aim of this study was to determine the genomic constitution and relationships between accessions of U. brizantha (2x and 4x), U. decumbens (2x and 4x) and U. ruziziensis (2x) via genomic in situ hybridization (GISH). Additionally, chromosome number and genome size were verified for the diploid accessions. The diploids U. brizantha and U. decumbens presented 2n = 2x = 18 chromosomes and DNA content of 1.79 and 1.44 pg, respectively. The GISH analysis revealed high homology between the diploids U. brizantha and U. decumbens, which suggests relatively low divergence time. The GISH using genomic probes from the diploid accessions on the tetraploid accessions chromosomes presented similar patterns, highlighting the genome B¹ present in both of the tetraploids. Based on GISH results, the genomic constitution was proposed for the diploid accessions of U. brizanhta (B¹B¹) and U. decumbens (B¹’B¹’) and both were pointed as donors of genome B¹ (or B¹’), present in the alotetraploid accessions.