What is Alternaria?

Alternaria is a dark-colored fungus widely distributed in nature. It is a common saprophytic fungus on soil, plants, food, and industrial materials, and it is also a common contaminating bacteria in the laboratory. Alternaria belongs to the family of fungi, Ascomycota, Ascomycota, Ascomycetes, Arachnidaceae, and Coccidiaceae. There are more than 50 species in the genus, the most common being Alternaria alternata. ^[1]

Alternaria Nees is one of the most widely distributed and economically important semi-known fungi in the world. 95

Exterior:

The colony is flocculent and grows rapidly. It is dark white in the early stage and darken in old age; the back is brown.

Under a light microscope:

Mycelia and conidia stalks brown-green, with transverse septum. Conidia are bar-shaped, with septum and mediastinum on the surface, forming a brick-like structure with thick walls, most of which are 3, with a short beak at the end, arranged in long straight or oblique chains; brown-green, more consistent in size , About 35 42m × 6 20m, more common in the air. ^[2]

The nature of Alternaria fungi is difficult to see under natural conditions, and only more than ten species of Alternaria are found under laboratory conditions. Although there are several genera that are considered to be sexual in Alternaria spp., Simmons thinks that they belong to the genus Lewia Barr & simmons after a comparative study of their sexual and similar genera.

Studies on the biological characteristics of Alternaria alternata, the pathogen of the black spot disease of pear, have shown that different strains cultured on PSA plates have significantly different average daily growth rates, spore production, colony color, and colony thickness. The suitable temperature for the growth of pathogenic bacteria is 20 30 , the optimal temperature is 28 , the optimal temperature for spore germination is 28 ; the suitable relative humidity for the growth of pathogenic bacteria is 50% to 100%, and the optimal relative humidity for growth is 98% to 100%. The germination of spores must have a high humidity of more than 98% relative humidity, and the highest germination rate in water droplets; the suitable pH for the growth of pathogenic hyphae is 4-12, the optimal growth pH is 7-8, and the optimal pH for spore germination The value is 7-8, and the pH value of the medium will change after the pathogenic bacteria are cultivated for a period of time. The pathogen can use a variety of carbon sources such as monosaccharides, disaccharides, and polysaccharides, as well as organic nitrogen and inorganic nitrogen. The most suitable carbon source is sucrose, and the most suitable nitrogen source is peptone. Ammonium sulfate and amine chloride will inhibit the mycelium of pathogens. Grow.

Alternaria mycelia is black and abundant in soil, air, and various organic matter as a culture. Its spores spread through the air. Under the conditions of incomplete sterilization, inadequate aseptic operation, high moisture content of the culture material and high temperature, it is beneficial to occur. ^[3]