Biological characteristics of the ultimate rot fungus of Dendrobium officinale and screening of its antibacterial plants
Dendrobium officinale Kimura et Migo is a perennial epiphytic herbaceous plant belonging to the Orchidaceae family. It is one of the sources of the precious Chinese medicinal herb “Dendrobium” and has the effects of enhancing the body’s immunity, benefiting the stomach and generating fluids, nourishing yin and clearing heat, and can also be used as a raw material for health products. It has a large market demand and high economic value. In order to meet the constantly expanding market demand, its artificial planting area is also constantly expanding, mainly distributed in Yunnan, Guizhou, Zhejiang, Fujian, Guangdong, and Sichuan in China.

With the vigorous development of industrial cultivation of Dendrobium officinale in various regions, the occurrence of diseases during its planting process has become increasingly serious. Among them, Dendrobium officinale soft rot is a devastating disease that often causes serious economic losses once it occurs in the field. The soft rot disease of Dendrobium officinale caused by the ultimate rot fungus occurs when the stem is soaked in water, gradually developing to the leaves. The soaked stem is black brown and necrotic, and the stem is prone to lodging and wet rot. It is relatively transparent with white hyphae appearing on the surface. Currently, chemical control is still the main method for preventing and controlling this disease in production, which poses problems such as pesticide residues, susceptibility to drug resistance, and environmental pollution. There are relatively few research papers on the biological control of soft rot disease in Dendrobium officinale, and most of them focus on indoor screening of biocontrol bacteria and plant derived pesticides, without conducting field experiments, and their field effects need further verification. Li et al. found that two endophytic fungi in Dendrobium plants have antagonistic activity against ultimate rot mold, and demonstrated through pot experiments that endophytic fungi in Dendrobium plants have good biological control effects on soft rot disease of Dendrobium officinale. Research by He et al. shows that 0.3% tetracycline AS, 1% sulfamethoxazole SC, 0.3% eugenol SL, and 1% osthole EW all have good inhibitory effects on the growth of ultimate fungal hyphae, with EC50 values of 0.13, 0.21, 0.29, and 5.04mg/L, respectively.

Plant disease pathogens are susceptible to factors such as light, temperature, pH, and nutrients. At the same time, 34 traditional Chinese medicinal materials, including Eugenia caryophyllata Thunb., which have a certain inhibitory effect on plant disease fungi, were preliminarily screened to investigate the ultimate biological characteristics of rot fungi and their antibacterial plants. The aim is to provide a theoretical basis for the research and development of efficient, low toxicity, and safe plant derived fungicides for the prevention and control of soft rot disease in Dendrobium officinale.

 

 

The research results of this article indicate that the ultimate rot mold can grow between 5-35 ℃, and the mycelial growth rate is the fastest at 30 ℃, which is conducive to the occurrence of diseases in this temperature environment. Bacteria can grow between pH 5 and 9, with the most suitable pH being 6-7. Nutrients are essential conditions for the growth of pathogens, and carbon and nitrogen sources are the two most basic and important elements in pathogen growth. Ultimate rot mold can utilize multiple carbon and nitrogen sources, among which glucose and soluble starch are the most suitable carbon sources. Lactose, mannitol, and inositol are not conducive to hyphal growth when used as carbon sources. Yeast extract is the most suitable nitrogen source, while ammonium sulfate, alanine, and glycine are not conducive to mycelial growth when used as nitrogen sources. The light conditions during 48 hours of cultivation had no significant effect on the growth of ultimate fungal hyphae.
This article studied the inhibitory effect of 34 water extracts of traditional Chinese medicine materials (concentration of 40mg dry sample/mL) on ultimate rot mold. The results showed that 23 water extracts of traditional Chinese medicine materials, including cloves, had inhibitory effects on ultimate rot mold, with inhibition rates ranging from 9.65% to 100%. Huang et al.’s study showed that when the concentration of anhydrous ethanol extract of wild plant dandelion in northwest Hubei was 40mg/mL, the antibacterial rate against ultimate rot mold was 53.47%, which was higher than the antibacterial rate of dandelion water extract at the same concentration in this article (51.09%). However, the difference in values was not significant, which may be due to differences in drug varieties, different extractant choices, or different ways of expressing extract concentrations. J ú lia et al. found that crude extract of aloe vera has an inhibitory effect on Pythium aphanidermatum, a fruit rot fungus belonging to the same genus. The water extracts of purple perilla seeds and leaves from different parts of perilla showed different antibacterial effects in this study. In future research, attention can be paid to the differences in the water extracts of the two, in order to find their antibacterial active substances and provide theoretical basis for the development of plant-based pesticides.
The two Chinese medicinal herbs with excellent antibacterial effects in this article are peppermint (96.48%) and clove (100%). Mint is a perennial herbaceous plant widely distributed in China, widely used in daily chemical, food, pharmaceutical and other fields. Previous antibacterial experiments on peppermint have mainly focused on human pathogens such as Staphylococcus aureus and Escherichia coli. Liu et al.’s study showed that a certain concentration of peppermint essential oil has a strong inhibitory effect on several pathogenic fungi that cause postharvest diseases in fruits. This article reports for the first time the inhibitory effect of peppermint water extract on the ultimate rot fungus of Dendrobium officinale. Its water extract has strong antibacterial effect, and peppermint is widely planted. Compared with other traditional Chinese medicinal materials, it has low cost and good potential for the prevention and control of Dendrobium officinale soft rot disease.

Lilac is a common Chinese herbal medicine and spice. Previous studies have shown that lilac has a certain inhibitory effect on the growth of various plant pathogens. Currently, in China, the registration of eugenol plant derived pesticides produced mainly from lilac has been completed and products have been formed, with registered crops including tomatoes, potatoes, grapes, and ornamental peonies. Research by He et al. has shown that 0.3% eugenol SL has a good inhibitory effect on the growth of ultimate rot mold, which is consistent with my own research results. At the same time, eugenol may be the main antibacterial active ingredient that inhibits ultimate rot mold in cloves. The results can provide reference for the field control of ultimate rot mold in Dendrobium officinale soft rot disease, and have certain guiding significance for expanding the scope of use of this plant derived pesticide.