Heterochromatin and rDNA 5S and 45S sites as reliable cytogenetic markers for castor bean (Ricinus communis, Euphorbiaceae)

The increasing need for renewable energy resources has led to higher demands for biofuel, a scenario where the castor bean (Ricinus communis L.) seed oil represents a promising source of raw material. Despite that, information regarding the genome organization of R. communis is still scarce, impairing the application of modern biotechnological and breeding procedures. The present work brings the first evaluation of the mitotic chromosomes of this species, including 10 potentially interesting accessions for cultivation in semi-arid environments aiming at the biofuel production. The approach included standard staining, fluorochrome staining (CMA/DAPI), fluorescent in situ hybridization (FISH) with rDNA 5S and 45S, as well as silver impregnation. All accessions were diploid with 2n = 2x = 20, displaying mainly metacentric chromosomes, with CMA-positive bands (GC-rich) in all pairs of the complement. After silver impregnation, one to 14 nucleoli were observed, while the FISH with rDNA 45S revealed two large sites and a variety of minor dots, and the DNAr 5S hybridized in a single pair. The observed features were discussed and compared with literature data regarding pachytene bivalents.