GISH-based comparative genomic analysis in Urochloa P. Beauv.

Area of Science:

• Plant genetics and genomics
• Forage crop improvement
• Cytogenetics

Background:

• The Urochloa genus is economically vital for forage production.
• Previous genomic proposals for U. brizantha (BBB¹B¹) and U. decumbens (B¹B¹B²B²) are incomplete, lacking the origin of B and B¹ genomes.
• U. ruziziensis is identified as the donor of genome B² in U. decumbens, but diploid ancestors for B¹ remain unknown.

Purpose of the Study:

• To elucidate the genomic constitution and interrelationships among diploid and tetraploid genotypes of U. brizantha, U. decumbens, and U. ruziziensis.
• To identify the ancestral donors of the B¹ genome in Urochloa allotetraploids.
• To verify chromosome number and genome size in diploid Urochloa genotypes.

Main Methods:

• Genomic in situ hybridization (GISH) was employed to analyze genomic constitution and relationships.
• Chromosome counts and DNA flow cytometry were used to determine chromosome number and genome size.
• GISH probes from diploid accessions were hybridized to chromosomes of tetraploid accessions.

Main Results:

• Diploid U. brizantha and U. decumbens possess 18 chromosomes and distinct DNA contents (1.79 pg and 1.44 pg, respectively).
• High homology was observed between diploid U. brizantha and U. decumbens, suggesting recent divergence.
• GISH analysis revealed that both diploid U. brizantha (B¹B¹) and U. decumbens (B¹'B¹') are the likely donors of the B¹ genome found in tetraploid Urochloa species.

Conclusions:

• The genomic constitution of diploid U. brizantha and U. decumbens has been proposed as B¹B¹ and B¹'B¹', respectively.
• These diploid genotypes are identified as the progenitors of the B¹ genome in allotetraploid Urochloa forages.
• The findings clarify the genomic origins, contributing to a better understanding of Urochloa evolution and breeding.