Symptoms and Control Methods of Aspergillus Disease in Lingzhi (Ganoderma lucidum)
Aspergillus belongs to the Deuteromycotina, Hyphomycetes, Moniliales, Moniliaceae, genus Aspergillus. There are many species of Aspergillus, and the most widespread harmful ones are Aspergillus flavus (A. flavus Link) and Aspergillus niger (A. niger Van Tieghem).
1. Morphological characteristics: The hyphae are colorless, septate and branched, shorter and thicker than those of Mucor. The conidiophores arise from specialized thick-walled swollen foot cells of the hyphae, unbranched, with the apex swelling into a vesicle. The surface of the vesicle produces radial single-layer or double-layer sterigmata. The conidia are borne at the tips of the sterigmata, ultimately forming unbranched chains. The vesicle, sterigmata and conidial chains together constitute the conidial head. The conidia are borne in chains at the tips of the sterigmata, with different colors and shapes, which is one of the bases for classification. On PDA medium, Aspergillus flavus colonies are initially slightly yellowish, then gradually turn yellow-green, and finally brown-green; the conidia are spherical and yellow-green. Aspergillus niger colonies are initially white, then black; the conidia are spherical and carbon black.
2. Disease development pattern
(1) Transmission route: Aspergillus is widely present in soil, air and decaying organic matter, and the conidia are spread by air currents.
(2) Occurrence conditions: Aspergillus mainly utilizes starch and also has the ability to decompose cellulose. Bamboo cultivation bed frames, under conditions of high humidity and poor ventilation, are extremely prone to developing it. The pH suitable for Aspergillus growth is near neutral. It has a relatively wide temperature adaptation range; the optimum growth temperature for Aspergillus niger is 20-30°C, and for Aspergillus flavus 25-30°C, and it can survive at 45°C in the compost for 30 minutes.
3. Damage symptoms: After the substrate is contaminated by Aspergillus flavus, the colonies are yellow to yellow-green, and those of Aspergillus niger are black; they grow and spread very rapidly, absorbing nutrients and water. The aflatoxin secreted by Aspergillus flavus is a very strong carcinogenic substance. Aspergillus niger and Aspergillus fumigatus produce high concentrations of spores that, when inhaled into the lungs, easily cause aspergillosis, also known as "mushroom worker's lung."
4. Control methods
(1) Do a good job of sanitation in the culture rooms, cultivation sites, etc., and eliminate sources of contamination.
(2) Strictly sterilize the culture medium; sawdust, straw materials, etc. need to be sun-dried before composting or sterilization.
(3) When mixing the substrate, adding 1×10-6 of Shibaogong or 5×10-6 carbendazim can inhibit the growth of Aspergillus flavus and Aspergillus niger.