Somaclonal Variation in Chrysanthemum × morifolium Protoplast Regenerants

Abstract

Chrysanthemum × morifolium protoplasts were isolated and regenerated to assess possible protoclonal variation in the regenerants. After a preliminary screening of the potential of different regeneration systems for protoplast regeneration, we produced a series of cut chrysanthemum 'Arjuna' leaf protoplast regenerants through liquid culture. Regenerants (54) were vegetatively propagated and grown under a commercial production system in 2 different seasons. All screened regenerants were significantly affected with regard to either flower number, flower size, flower weight, leaf weight, stalk weight, or plant size. A significant plant size reduction in 43/52 and 48/49 regenerants for both seasons was the most recorded effect. Also a reduction in flowering induction time up to 10 days, altered flower types and colors were observed. Differences between growing seasons were notable. Possible molecular backgrounds including genome size variation and commercial applications in breeding of chrysanthemum are discussed.

Keywords: Asteraceae; flower traits; genome size; in vitro; ornamentals; phenotype; plant breeding; protoclonal variation.

FIGURE 1

Experimental setup. In experiment 1, 16 cut and pot Chrysanthemum × morifolium cultivars were selected and the regeneration potential of protoplasts from 2 different tissues was tested in 2 different culture systems. A regeneration system (cultivar × tissue type × culture type) was selected. The regenerants of the selected cultivar were further referred to as the AR-series. Following, a larger regenerant batch (RS series) was produced through the selected system. In experiment 2, mother plants were grown from all AR and RS regenerants and used for cutting production. These cuttings were compared to the original cultivar through assessment of phenotypic parameters. For a second and independent assessment, new mother plants were produced from the old ones.

FIGURE 2

Morphological variation in Chrysanthemum × morifolium protoplast regenerants: (A) ‘Golden Surfer’ regenerants GSR1, GSR2, and GSR7, all with compact growth and delayed flowering; (B) ‘Le Bonheur’ regenerants LBR1 (normal phenotype), LBR3 (advanced flower bud formation), and LBR5 (compact growth, deformed leaves).

FIGURE 3

Chrysanthemum × morifolium ‘Arjuna’ protoplast regenerants, different phenotypes in 2017: (A) overview of phenotypic greenhouse trials; (B) V-C leaves; (C) AR5 leaves; (D) AR14 leaves; (E) V-C flower; (F) yellowish disk florets (RS25); (G) greenish disk florets and tubular-type flower (RS37); (H) reddish ray florets [RS48(2017)_2]. Scale bar = 5 cm.

FIGURE 4

Phenotypic screening of Chrysanthemum × morifolium ‘Arjuna’ protoplast regenerants: density plots for parameters RT3 (retention time 3), FN (flower number), FS (flower size), FW (flower weight), LW (leaf weight), SW (stalk weight), and PS (plant size) independently assessed in August 2017 (blue) and May 2018 (brown). Controls are indicated.

FIGURE 5

Pearson correlation matrix of phenotypic parameters FN (flower number), FS (flower size), FW (flower weight), LW (leaf weight), SW (stalk weight), and PS (plant size) assessed on Chrysanthemum × morifolium ‘Arjuna’ protoplast regenerants in 2 independent trials in 2017 (upper value) and 2018 (lower value). Significant correlations (P < 0.05) are labeled with *.