Enhancement of Growth, Flowering and Corm Freesia Hybrida Plant via Rice Organic Residue Application and Chelated Zinc Spray

A pot trial was conducted to identify the effect of adding rice organic residues (ROR) to the potting soil and spraying chelated zinc (CZn) on the growth, flowering, and corm characteristics of the Freesia hybrida plant. An RCBD experiment was adopted with two factors and three replicates. ROR comprised three levels (0, 4, and 8%), and CZn included three concentrations (0, 20, and 40) mg.L−1. The findings revealed that applying ROR at 8% and spraying CZn at 20 mg.L−1 significantly increased leaf number, shoot dry weight, total chlorophyll content in fresh leaves, and total soluble carbohydrate content in dry leaves (6.66 leaves. plant−1, 8.76 g DW, 48.79 mg.100 g−1 FW, and 1.50 g DW) respectively. Also, the same treatment combination realized significant results for the number of florets per inflorescence, floret diameter, floret vase life, number of corms per plant, and corm diameter by (12.85 florets. inflorescence−1, 7.03 cm, 8 days, 3.66 corms. plant−1, and 2.33 cm) consecutively. Further, adding ROR at 8% and spraying CZn at 40 mg.L−1 significantly increased the number of inflorescences (5.33 inflorescences. plant−1) and inflorescence length (39.10 cm).

Identification and Evaluation of Aromatic Volatile Compounds in 26 Cultivars and 8 Hybrids of Freesia hybrida

Freesia hybrida is a group of cultivars in the genus Freesia with a strong floral scent composed of diverse volatile organic compounds (VOCs). In this study, the VOCs of 34 F. hybrida were extracted and analyzed by headspace solid phase microextraction and gas chromatography mass spectrometry (HS-SPME-GC-MS). A total of 164 VOCs whose relative contents were higher than 0.05% were detected. The numbers of VOCs in all germplasms differed between 11 to 38, and the relative contents ranged from 32.39% to 94.28%, in which most germplasms were higher than 80%. Terpenoids, especially monoterpenes, were the crucial type of VOCs in most germplasms, of which linalool and D-limonene were the most frequently occurring. Principal component analysis (PCA) clearly separated samples based on whether linalool was the main component, and hierarchical clustering analysis (HCA) clustered samples into 4 groups according to the preponderant compounds linalool and (E)-β-ocimene. Comparison of parental species and hybrids showed heterosis in three hybrids, and the inherited and novel substances suggested that monoterpene played an important role in F. hybrida floral scent. This study established a foundation for the evaluation of Freesia genetic resources, breeding for the floral aroma and promoting commercial application.

Effect of Planting Time and Corms Treatment with Gibberellic Acid on Growth, Flowering, and Vase Life of Freesia hybrida ‘Corona’

Freesia hybrida is one of the most important cut flowers with a short vase life. The present study was conducted to explain the effect of the two planting dates December 1st and 15th and soaking corms before planting in gibberellic acid at concentrations of 0, 75, and 150 mg·L−1 on the growth, flowering, and flowers quality of Freesia hybrida ‘Corona’. A larger diameter of the inflorescence stem and floret head, fresh weight of inflorescence, and longer vase life were obtained when planted on December 1st. Soaking the corms in a GA3 solution of 150 mg·L−1 before planting significantly extended the vase life compared to the control. Finally, it can be concluded that the planting of corms soaked in a solution of 150 mg·L−1 GA3 on December 1st in unheated greenhouses can improve the growth, development, and quality of flowers of Freesia hybrida ‘Corona’.

Enzymatic and transcriptomic analysis reveals the essential role of carbohydrate metabolism in freesia (Freesia hybrida) corm formation

Starch and sucrose metabolism plays a crucial role in the formation and development of bulbs in bulbous plants. However, these mechanisms remain unclear and unexplored in the corms of Freesia hybrida. Herein, we investigated the dynamics of the major form of carbohydrates and related enzyme activities and profiled the transcriptome of freesia corms at four developmental stages with the aim to reveal the relation between the expression of genes involved in the metabolism of carbohydrates and the accumulation of carbohydrates in corm developmental stages for further exploring the mechanism on the starch and sucrose metabolism regulating the formation and development of corms in F. hybrida. The content of starch, sucrose and soluble sugars followed an overall upward trend across the corm developmental stages. Activities of the adenosine diphosphoglucose pyrophosphorylase, starch branching enzyme and β-amylase generally followed the pattern of the starch and sucrose levels. Activities of sucrose phosphate synthase increased from corm formation till the initial swelling stage and subsequently reached a plateau. Activities of invertase and sucrose synthase peaked at the later rapid swelling stage. These suggested that the starch and sucrose dynamics paralleled corm swelling under the action of metabolic enzymes. A total of 100,999 unigenes were assembled in the transcriptomic analysis, and 44,405 unigenes of them were annotated. Analysis based on Clusters of Orthologous Groups suggested that carbohydrate transport and metabolism (9.34% of the sequences) was prominent across the corm developmental process. In total 3,427 differentially expressed genes (DEGs) were identified and the enrichment analysis detected starch and sucrose metabolism as a critical pathway in corm development, especially at the rapid swelling stage. Further, DEGs encoding key carbohydrate-metabolizing enzymes were identified and correlated to enzyme activities and carbohydrate accumulation. The results construct a valuable resource pool for further molecular-level studies, which are helpful for metabolic regulation of carbohydrates and improvement in F. hybrida.

Analysis of Relative Scent Intensity, Volatile Compounds and Gene Expression in Freesia “Shiny Gold”

Scent is one of the most important economic traits in Freesia hybrida. “Shiny Gold”, a popular cultivar in South Korea, is widely cultivated for its scent. The relative scent intensity of “Shiny Gold” was approximately 16% higher in full-bloomed flower when compared to the yellow bud stage, while tissue-specifically, tepals showed higher intensity in electronic-nose (e-nose) analysis. E-nose analysis also showed that the scent intensity of “Shiny Gold” was higher and lower than “10C3-424” and “10C3-894”, respectively, and was similar to “Yvonne”. These results correlated to those of the olfactory tests. In total, 19 volatile compounds, including linalool, β-ocimene, D-limonene, trans-β-ionone were detected in gas chromatography–mass spectrometry analysis. Among these, linalool was the major volatile compound, accounting for 38.7% in “Shiny Gold”. Linalool synthase and TPS gene expression corresponded to the scent intensity of the four cultivars, with the lowest expression in the “10C3-424”. TPS 2, TPS 3, TPS 5, TPS 6 and TPS 8 were highly expressed in both bud and flower in “Shiny Gold”, while the expression of TPS 4 was lower, relative to other TPS genes in both the flowering stages. These results may aid in enhancing scent composition in Freesia cultivars using marker-assisted selection.

MYB repressors and MBW activation complex collaborate to fine-tune flower coloration in Freesia hybrida

Floral anthocyanin has multiple ecological and economic values, its biosynthesis largely depends on the conserved MYB-bHLH-WD40 (MBW) activation complex and MYB repressors hierarchically with the MBW complex. In contrast to eudicots, the MBW regulatory network model has not been addressed in monocots because of the lack of a suitable system, as grass plants exhibit monotonous floral pigmentation patterns. Presently, the MBW regulatory network was investigated in a non-grass monocot plant, Freesia hybrida. FhMYB27 and FhMYBx with different functional manners were confirmed to be anthocyanin related R2R3 and R3 MYB repressors, respectively. Particularly, FhMYBx could obstruct the formation of positive MBW complex by titrating bHLH proteins, whereas FhMYB27 mainly defected the activator complex into suppressor via its repression domains in C-terminus. Furthermore, the hierarchical and feedback regulatory loop was verified, indicating the synergistic and sophisticated regulatory network underlying Freesia anthocyanin biosynthesis was quite similar to that reported in eudicot plants.

Dynamics and Transcriptome Analysis of Starch and Sucrose Metabolism During Corm Development in Freesia Hybrida

Background Starch and sucrose metabolism plays a crucial role in the formation and development of bulbs in bulbous plants, which, however, remains unclear and unexplored in the corms of Freesia hybrida, one kind of famous bulbous flower. Herein, we investigated the dynamics of the major form of carbohydrates and related enzyme activities and profiled the transcriptome of freesia corms at four developmental stages with the aim to reveal the relation of starch and sucrose metabolism to corm development and the transcriptional regulation of this metabolic process.Results The content of starch, sucrose and soluble sugars followed an overall upward trend across the corm developmental stages. Activities of the adenosine diphosphoglucose pyrophosphorylase, starch branching enzyme and β-amylase generally followed the pattern of the starch and sucrose level. Activities of sucrose phosphate synthase increased from corm formation till the initial swelling stage and subsequently reached a plateau. Activities of invertase and sucrose synthase peaked at the later rapid swelling stage. Transcriptome analysis revealed a total of 100,999 unigenes, out of which 44,405 unigenes were annotated. Analysis based on Clusters of Orthologous Groups suggested that carbohydrate transport and metabolism (9.34% of the sequences) was prominent across the corm developmental process. Totally 3427 differentially expressed genes were identified and the enrichment analysis directed starch and sucrose metabolism a critical pathway in corm development especially at the rapid swelling stage. Genes encoding key carbohydrate-metabolizing enzymes were identified and their differential expression related to corm development was explored.Conclusions The comparative transcriptome analysis discloses essential roles of starch and sucrose metabolism and the genetic mechanism related to the corm development. The results construct a valuable resource pool for further molecular-level studies, which are helpful for metabolic regulation of carbohydrates and improvement in molecular breeding of Freesia hybrida.