A Fumigation-Based Surface Sterilization Approach for Plant Tissue Culture

Herbal smoke fumigation for controlling Penicillium crustosum in fresh walnuts

Fresh walnuts have a high water content and are susceptible to decay, and controlling fungal contamination during storage is vital to walnut marketing. In this research, the dominant pathogenic fungus of fresh walnuts was first identified as Penicillium crustosum by morphological and molecular methods. The antifungal effect of herbal smoke fumigation was tested in vitro and in vivo, including Myristica fragrans Houtt., Aucklandia lappa Decne., Eugenia caryophyllata Thunb., Atractylodes lancea (Thunb.) DC., Shiraia bambusicola Henn., Artemisia argyi Lévl. et Vant. The results demonstrated that smoke from all six herbs successfully inhibited P. crustosum growth, and A. argyi smoke produced the best antifungal effect, which contained higher contents of phenol (17.1%), eugenol (13.7%), hexacosane, tetracontane, heneicosane, linolenic acid and other antimicrobial components by gas chromatography-mass spectrometry. Interestingly, optical transmittance data were found to correlate with antifungal capacity, revealing that a formed physical barrier combined with the above antimicrobial compositions, to participate in mold controlling together. Finally, fumigation with A. argyi smoke was tested in a real storage situation at proper dose, which not only dramatically controlled fungal contamination (>70%), but also maintained better odor and taste without oxidative rancidity or other adverse effects. This is the first report in which herbal smoke fumigation was adopted to preserve fresh walnut, providing a new way to reduce mold contamination and maintain quality of fresh walnuts in a natural and safe manner. More research on the application of herbal smoke fumigation to agricultural products in post-harvest storage is needed to explore the conditions and products for which it can be used successfully.

Optimization of callus induction and proliferation of Paeonia lactiflora Pall. and Agrobacterium-mediated genetic transformation

Paeonia lactiflora Pall. is an important ornamental plant with high economic and medicinal value, which has considerable development prospects worldwide. The lack of efficient tissue culture techniques and genetic transformation systems has become a master obstacle for P. lactiflora research. The purpose of the present study focuses on obtaining an efficient and stable genetic transformation method using callus as the receptor and exploring an efficient protocol for callus induction and proliferation associated with P. lactiflora. Callus induction and proliferation were performed using MS medium with various concentrations of 2,4-Dichlorophenoxyacetic acid (2,4-D), 1-Naphthaleneacetic acid (NAA), 6-Benzylaminopurine (6-BA) and thidiazuron (TDZ). The sensitivity of callus to kanamycin and cefotaxime was determined. Several parameters such as Agrobacterium cell density, infection time and co-culture duration were studied to optimize transformation efficiency. Agrobacterium strains EHA105 and pBI121 binary vector harboring the β-glucuronidase (GUS) gene were used for transformation. Expression of the GUS reporter gene was detected by GUS assay, polymerase chain reaction (PCR) and Quantitative Real-time PCR (RT-qPCR). The MS medium containing 1.0 mg·L^-1 NAA, 0.5 mg·L^-1 2,4-D and 0.5 mg·L^-1 TDZ was optimal for callus induction and MS medium containing 0.5 mg·L^-1 NAA, 1.0 mg·L^-1 2,4-D and 0.5 mg·L^-1 TDZ was the best for callus proliferation. The concentrations of kanamycin and cefotaxime used for screening positive callus were 125 mg·L^-1 and 200 mg·L^-1, respectively. Among various combinations analyzed, the best transformation result was obtained via the 25 min of infection of Agrobacterium at 0.6 OD₆₀₀ and 3 d of co-culture. Overall, this study provided technical support and theoretical guidance for improving the callus induction and proliferation efficiency and the study of gene function in P. lactiflora.

Isolation, Identification and Pollution Prevention of Bacteria and Fungi during the Tissue Culture of Dwarf Hygro (Hygrophila polysperma) Explants

Microbial contamination causes serious damage in plant tissue culture, and attention is always being paid regarding how to control and prevent the unwanted pollution. Dwarf hygro (Hygrophila polysperma) is a popular ornamental aquatic plant and its tissue culture has been reported, but the microbial pollution and the cure of microbial pollution was unknown. In this study, a number of bacteria and fungi were isolated from contaminants in MS culture media. Based on the 16S rDNA and ITS sequencing, it was identified that fifteen bacteria belong to Bacillus, Enterobacter, Pantoea, Kosakonia, Ensifer and Klebsiella, and three fungi belong to Plectosphaerella, Cladosporium and Peniophora, respectively. In addition, some drugs were further tested to be free of the bacteria and fungi pollution. The results revealed that 10 μg/mL of kanamycin, 5 μg/mL of chloramphenicol, and 0.015625% potassium sorbate could be applied jointly in MS media to prevent the microbial pollution, and the survival rate of H. polysperma explants was highly improved. This study reveals the bacteria and fungi species from the culture pollution of H. polysperma and provides a practical reference for optimizing the tissue culture media for other aquatic plants.