Chromosome set doubling and ploidy stability in synthetic auto- and allotetraploid of Eucalyptus: from in vitro condition to the field

• DOI: 10.1007/s11240-019-01627-1
• Publication Date: 2019-05-10T10:47:00Z
• Authors: Alex Junior Silva; Carlos Roberto Ca...; Wellington Ronild...
• Keywords: Polyploid; Germ plasm; Colchicine; Chromosome number

Given the increased demand for wood producing species with fast growth, chromosome set doubling (CSD) is an option to enrich germplasm banks and breeding programs with synthetic polyploids in relatively short time. Here, we aimed to establish a feasible practice of an in vitro procedure to create solid polyploid Eucalyptus, and to verify the DNA ploidy level fidelity in newly synthetized polyploids. We treated 1.0 and 1.5 cm shoot tips of Eucalyptus grandis with colchicine in distinct times and concentrations and achieved between 0 and 66.67% autotetraploids, totaling 87 plantlets from all CSD treatments. However, a reversion to diploidy and/or mixoploidy was observed in 35.5% and 22.0% of total plantlets in the first and second ploidy level assessments, respectively. Based on the results, a second CSD assay was performed for 1.5 cm shoot tips of Eucalyptus grandis, Eucalyptus urophylla, Eucalyptus benthamii and E. urophylla × E. grandis, which we treated with 1.5 mM colchicine for 36 h. Auto- and allotetraploidy rates ranged from 40.8 to 65.5%, and again DNA ploidy level changes were detected in in vitro and ex vitro individuals. In conclusion, fine adjustments of the antitubulin concentration and exposure time are needed for each explant and genotype/species to CSD from apical meristem stem cells. Since ploidy stability was found to be a dramatic problem in Eucalyptus CSD, we promote recurrent DNA ploidy level screening to achieve solid auto- and allotetraploids propagation and to identify undesired mixoploids and diploids in in vitro and ex vitro conditions. Eucalyptus auto- and allotetraploids were obtained, enriching the germplasm banks. Looking for DNA ploidy level, changes were identified in some synthetic tetraploids, evidencing the ploidy instability as a dramatic problem.