Can Knowledge of Genetic Distances, Genome Sizes and Chromosome Numbers Support Breeding Programs in Hardy Geraniums?

Abstract

Breeding programs in ornamentals can be facilitated by integrating knowledge of phylogenetic relatedness of potential parents along with other genomic information. Using AFLP, genetic distances were determined for 59 Geranium genotypes, comprising 55 commercial cultivars of the three subgenera of a total collection of 61 Geranium genotypes. A subgroup of 45 genotypes, including intragroup and intergroup hybrids, were selected and further characterized for genome sizes and chromosome numbers. The variation in genome size ranged from 1.51 ± 0.01 pg/2C to 12.94 ± 0.07 pg/2C. The chromosome numbers ranged from 26 to 108-110 with some hybrids showing an aberrant number of chromosomes based on their parents' constitution. All chromosome numbers of Geranium are an even number, which presumes that unreduced gametes occur in some cross combinations. Overall, parental difference in genome size and chromosome number were not limiting for cross compatibility. Good crossing compatibility was correlated to a Jaccard similarity coefficient as parameter for parental relatedness of about 0.5. Additionally, parent combinations with high differences in the DNA/chromosome value could not result in a successful cross. We expect that our results will enable breeding programs to overcome crossing barriers and support further breeding initiatives.

Keywords: 2C value; AFLP; Geraniaceae; Jaccard similarity coefficient; chromosome counts; cross compatibility; hybridization; hybrids.

Figure 1

PCoA based on AFLP data of 61 genotypes of Geranium with the X- and Y-axis comprising 17.6% and 13.8% of the variation, respectively.

Figure 2

PCoA based on AFLP data of genotypes of subgenus Geranium (in total 45 plants) with X and Y-axis explaining 21.9% and 9.9% of the variation, respectively.

Figure 3

Chromosome counts of Geranium genotypes: (A) G. phaeum ‘Angelina’—3.52 pg/2C and 2n = 28; (B) G. wallichianum ‘Sylvia’s surprise’—6.78 pg/2C and 2n = 38; (C) G. × riversleaianum ‘Mavis Simpson’—4.31 pg/2C and 2n = 38; (D) G. ‘Azure Rush’—8.90 pg/2C and 2n = 42; (E) G. ‘Catherine Deneuve’—6.95 pg/2C and 2n = 54; (F) G. himalayense ‘Derrick Cook’—7.49 pg/2C and 2n = 56; (G) G. sanguineum ‘Blushing Turtle’—7.80 pg/2C and 2n = 66; (H) G. ‘Tiny Monster’—12.94 pg/2C and 2n = 108/110 (bar = 10 µm).