A major constraint affecting the quality and productivity of chrysanthemum is the unusual period of low temperature occurring during early spring, late autumn, and winter. Yet, there has been no systematic investigation on the genes underlying the response to low temperature in chrysanthemum. Herein, we used RNA-Seq platform to characterize the transcriptomic response to low temperature by comparing different transcriptome of Chrysanthemum nankingense plants and subjecting them to a period of sub-zero temperature, with or without a prior low temperature acclimation. Six separate RNA-Seq libraries were generated from the RNA samples of leaves and stems from six different temperature treatments, including one cold acclimation (CA), two freezing treatments without prior CA, two freezing treatments with prior CA and the control. At least seven million clean reads were obtained from each library. Over 77% of the reads could be mapped to sets of C. nankingense unigenes established previously. The differentially transcribed genes (DTGs) were identified as low temperature sensing and signalling genes, transcription factors, functional proteins associated with the abiotic response, and low temperature-responsive genes involved in post-transcriptional regulation. The differential transcription of 15 DTGs was validated using quantitative RT-PCR. The large number of DTGs identified in this study, confirmed the complexity of the regulatory machinery involved in the processes of low temperature acclimation and low temperature/freezing tolerance.

Chrysanthemum is among the top ten traditional flowers in China, and one of the four major cut flowers in the world, but the growth of chrysanthemum is severely restricted by high temperatures which retard growth and cause defects in flowers. DREB (dehydration-responsive element-binding) transcription factors play important roles in the response to abiotic and biotic stresses. However, whether the DREB A-6 subgroup is involved in heat tolerance has not been reported conclusively. In the present study, CmDREB6 was cloned from chrysanthemum (Chrysanthemum morifolium) ‘Jinba’. CmDREB6, containing a typical AP2/ERF domain, was classed into the DREB A-6 subgroup and shared highest homology with Cichorium intybus L. CiDREB6 (73%). CmDREB6 was expressed at its highest levels in the leaf. The CmDREB6 protein localized to the nucleus. Based on the yeast one hybrid assay, CmDREB6 showed transcription activation activity in yeast, and the transcriptional activation domain was located in the 3 ‘end ranging from 230 to 289 amino acids residues. CmDREB6 overexpression enhanced the tolerance of chrysanthemum to heat. The survival rate of two transgenic lines was as high as 85%, 50%, respectively, in contrast to 3.8% of wild-type (WT). Over-expression of CmDREB6 promoted the expression of CmHsfA4, CmHSP90, and the active oxygen scavenging genes CmSOD and CmCAT. In this study, DREB A-6 subgroup gene CmDREB6 was cloned from chrysanthemum ‘Jinba’. Overexpression of CmDREB6 enhanced heat tolerance of chrysanthemum by regulating genes involved in the heat shock response and ROS homeogenesis.

ICE (Inducer of CBF Expression) family genes play an important role in the regulation of cold tolerance pathways. In an earlier study, we isolated the gene CdICE1 from Chrysanthemum dichrum and demonstrated that freezing tolerance was enhanced by CdICE1 overexpression. Therefore, we sought to determine the mechanism by which ICE1 family genes participate in freezing tolerance.

The objective of this study was to identify the major volatile compounds and their relative concentrations in flowers of different chrysanthemum cultivars and their wild relatives. The volatile organic components of fresh flowers were analyzed using a headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry. In total, 193 volatile organic components were detected; the major scent components were monoterpenoids and oxygenated monoterpenoids, which accounted for 68.59%–99.93% of the total volatiles in all tested materials except for Chrysanthemum indicum collected from Huangshan, in which they accounted for only 37.45% of total volatiles. The major volatile compounds were camphor, α-pinene, chrysanthenone, safranal, myrcene, eucalyptol, 2,4,5,6,7,7ab-hexahydro-1H-indene, verbenone, β-phellandrene and camphene. In a hierarchical cluster analysis, 39 accessions of Chrysanthemum and its relatives formed six clusters based on their floral volatile compounds. In a principal component analysis, only spider type flowers were located closely on the score plot. The results of this study provide a basis for breeding chrysanthemum cultivars which desirable floral scents.

Sustained monoculture often leads to a decline in soil quality, in particular to the build-up of pathogen populations, a problem that is conventionally addressed by the use of either fungicide and/or soil fumigation. This practice is no longer considered to be either environmentally sustainable or safe. While the application of organic fertilizer is seen as a means of combating declining soil fertility, it has also been suggested as providing some control over certain soil-borne plant pathogens. Here, a greenhouse comparison was made of the Fusarium wilt control efficacy of various treatments given to a soil in which chrysanthemum had been produced continuously for many years. The treatments comprised the fungicide carbendazim (MBC), the soil fumigant dazomet (DAZ), the incorporation of a Paenibacillus polymyxa SQR21 (P. polymyxa SQR21, fungal antagonist) enhanced bio-organic fertilizer (BOF), and applications of BOF combined with either MBC or DAZ. Data suggest that all the treatments evaluated show good control over Fusarium wilt. The MBC and DAZ treatments were effective in suppressing the disease, but led to significant decrease in urease activity and no enhancement of catalase activity in the rhizosphere soils. BOF including treatments showed significant enhancement in soil enzyme activities and microbial communities compared to the MBC and DAZ, evidenced by differences in bacterial/fungi (B/F) ratios, Shannon–Wiener indexes and urease, catalase and sucrase activities in the rhizosphere soil of chrysanthemum. Of all the treatments evaluated, DAZ/BOF application not only greatly suppressed Fusarium wilt and enhanced soil enzyme activities and microbial communities but also promoted the quality of chrysanthemum obviously. Our findings suggest that combined BOF with DAZ could more effectively control Fusarium wilt disease of chrysanthemum.