In July 2024, Ms. Deng from Deqing County, Zhejiang Province, posted online that an apple in her house that had been forgotten for many days was "moldy" and actually grew mushrooms!
Source: A social platform @Peirong
From the photos she provided, you can see that the apple is mostly intact on the outside, but a few white mushrooms have emerged from the top. This phenomenon is very surprising because most mushrooms can only grow on soil and decaying wood, feeding on decaying organic matter. This apple still looks good, how can it grow mushrooms?
It didn't take long for Ms. Deng to receive a private message from a Ph.D. student at the Kunming Institute of Botany, Chinese Academy of Sciences, saying that she wanted to buy apples for research. Later, according to the doctor's instructions, Ms. Deng wrapped the apples in plastic wrap and put them in the refrigerator, put them in a foam box with ice packs the next day, and sent them to the Kunming Institute of Botany, Chinese Academy of Sciences free of charge.
Seeing this ups and downs of experience, netizens lamented that while this apple was finally able to exert its scientific research value, the comment area was also full of joy, and some netizens also jokingly called it the "king of fruit fungi"......
Source: A social platform @Peirong
So why haven't I seen other apples grow mushrooms before? What is the scientific value of this mushroom? Let's find out today.
What are mushrooms on apples?
Through further sequencing identification, the researchers found that this mushroom is Schizophyllum commune, which is the type species of Schizophyllum schizophyllum and the most common species of the genus, which is extremely tenacious and widely distributed around the world. Almost at any time of the year, you can find them on branches and stakes in the wild.
Named for its unique longitudinally dehisced folds, the fungus usually prefers to grow on withered, decaying wood, has a strong lignin decomposition ability, and is a saprophytic fungus. In addition, Schizomyces is also considered a plant pathogen with strong mycelial activity that can infect live trees such as apples, citrus, and olives, causing wood decay, blackened bark, and leaf necrosis. This wood rot disease mainly occurs on aging and weak disease resistant trees, and apple trees have been reported to be infected with Schizomyces at home and abroad.
Therefore, it is reasonable to assume that Schizophyllum initially infects the apple tree, causing it to carry the spores or hyphae of Schizophyllum and grow on apples when environmental conditions are suitable, such as during the rainy season.
Schizophyllum grown in the wild. Source: Author
As the "King of Fruit Fungi" caused heated discussions, some netizens even posted the schizofungi growing on other substrates, the most unique of which is the schizofungi growing on garlic. Many people have questions, isn't garlic sterilized? How can you still grow mushrooms?
Actually, this is the same question as why garlic is moldy. The main antibacterial active ingredient of garlic is allicin, but allicin does not naturally exist in garlic cells, and only by destroying the tissue structure of garlic through mechanical external force can the alliin and alliinase in its body combine to form allicin.
The mycelial invasion of the fungus does not cause significant damage to the tissue cells, so only trace amounts of allicin are produced, which is not enough to defend against the invasion of the fungus. Therefore, the antibacterial properties of garlic do not prevent its own decay, nor can it prevent the infection of schizobacteria.
Source: References[5]
Why do non-perishable apples grow mushrooms?
In fact, when the mushroom-growing apple is cut, it can be seen that the mycelium has infected the inside of the apple and gradually expands outward. The inside of this apple has been visibly rotten. If you look closely at the mushroom on the top of the apple, you can still find that the seemingly intact apple has deteriorated on the skin.
Source: A social platform @ I really can't drink anymore
Food spoilage is caused by bacteria and various fungi that, when they break down food, produce various waste products that can be harmful to human health, such as Aspergillus flavus, which likes to multiply on grains in large quantities, and the aflatoxin it produces is considered to be the most toxic and strongest natural compound for liver carcinogenesis.
Life experience tells us that apples are a very shelf-stable fruit, and sometimes they don't spoil after a few months, but they lose moisture and become shriveled. So why is this apple like this?
It turns out that apples secrete a layer of wax during growth, which can effectively prevent external microorganisms from invading the pulp. However, the hollow of the apple peduncle is a weak point that leads directly to the pit and is therefore most susceptible to microbial invasion, which is also chosen by the schizophyllum to grow.
The shape of the apple Source: Reference [6]
If you look closely, you will find that natural mushrooms like to grow in the crevices of the wood, preferably where there are wounds, which makes it easier for the mushroom hyphae to invade the inside of the substrate. Therefore, apples and other fruits with wounds should be eaten as soon as possible, otherwise they are more likely to spoil. When storing apples on a daily basis, you can put them in the refrigerator to refrigerate, and low temperature can inhibit the growth of microorganisms and prolong the storage time.
Apples can be eaten, and schizophritic bacteria can also be eaten, so can apples with schizofungi still be eaten? The answer is no! Food spoilage is a multi-microbial involvement, and although Schizomyces may have a major predominance, it is likely that other bacteria and fungi are present, and the substances they produce in the process of metabolism are potentially harmful to health.
Taking a step back, even if there are only schizomycetes in apples, isn't eating apples full of schizomycelium the same as eating raw mushrooms? Still not recommended.
It turns out that we have already eaten schizata!
As early as 2000 years ago, the folk of Yunnan in mainland China had the habit of eating schizomes, and the common people called it "white ginseng". The classic method is "steamed eggs with white ginseng", which can also be fried directly, which is delicious and nourishing, but the taste is hard and needs to be soaked in advance.
People in Mexico, India and other places also have the habit of eating schizomes. One of the advantages of Schizophyllum over other edible mushrooms is that it has a hard and elastic texture, which is not easy to rot and is easy to sell. At present, due to the limited yield of artificial cultivation, the price of schizomyces is high, and the price of dried products can reach 50 yuan/catty.
Schizomycetes growing in cracks in decaying wood Source: References[7]
After tasting by the researchers, the schizophyllum growing on apples did not smell like apples. In fact, this result is also conceivable.
The flavor substances in mushrooms include non-volatile free amino acids, soluble sugars, flavor nucleotides, etc., and volatile flavor substances include sulfur-containing compounds and alcohols, ketone compounds, aldehydes, esters, etc., the production of these substances is controlled by genes, and the same is true for flavor substances in apples.
In different growing substrates, due to differences in environmental conditions, the same mushroom may secrete more or less of these flavor compounds, which may affect the taste of the mushroom, but it is unlikely to lead to changes in the genes that produce these flavor compounds, let alone the directional possession of the genes that produce apple flavor compounds. Take an example from plants: some watermelons will be grafted onto the seedlings of pumpkins, which is to use the developed root system of pumpkins to absorb more nutrients in the soil for watermelons to grow, so that the watermelons will taste better, but will not have a pumpkin flavor.
Why researchers collect
Schizophyllum on apples?
The goal of edible fungus breeding is to obtain excellent varieties with high yield, high quality, high resistance and high content of bioactive substances. Under natural conditions, some wild edible mushrooms will mutate, and the beneficial mutations can be used continuously to obtain new varieties that people need.
This important breeding method is called "artificial selection breeding", and the excellent shiitake mushroom varieties (Lentinula edodes) 7401, Guangxiang 5, 241 and 8210 are all screened by artificial selection, which is why researchers who do edible mushroom cultivation will collect a wide range of wild edible mushroom resources of a single species.
At present, it is clear that the hyphae of the schizomyces growing on this apple are active and fast, and the next cultivation experiment needs to be carried out to see if it is high-yielding. In fact, for Schizomyces, it may be more important to breed varieties that are not so hard, so then it is necessary to evaluate its taste.
Source: A social platform @ I really can't drink anymore
There is a more efficient method in edible fungus breeding technology - radiation mutagenesis breeding, which is to use physical or chemical mutagens to treat the cell population, increase its mutation rate, and then select the mutant strain that meets the breeding goal from the population. The mycelium of Schizophyllum has been in space many times, and the radiation from space has been used to change the genetic characteristics, thus breeding the better-tasting Schizophyllum on the market.
It is important to note that Schizomyces is also a common human pathogen, and it infects humans with a similar morphology to molds. Most cases involve the respiratory tract, including bronchopulmonary disease and sinusitis, and occur in both immunocompetent and immunocompromised people. This is a warning not to put it in our nose when collecting and handling Schizophyllum spores to prevent inhalation of Schizophyllum spores.
bibliography
[1] Mao Xiaolan, 2000. Macrofungi of China. Henan Science and Technology Press.
[2] Yu Zipeng, Li Ningyang, Gong Zhiqing, et al. Science and Technology of Food Industry,2024,45(02):373-379.DOI:10.13386/j.issn1002-0306.2023020269.
[3] Fu Lizhong, Wu Xueqian, Wei Hailong, et al. Journal of Edible Fungi,2005,(03):63-68.DOI:10.16488/j.cnki.1005-9873.2005.03.012.
[4] Chowdhary A, Kathuria S, Agarwal K, et al. Recognizing filamentous basidiomycetes as agents of human disease: a review[J]. Medical Mycology, 2014, 52(8): 782-797.
[5]https://mp.weixin.qq.com/s/kvbog7_IoIEyPBRx1iVEog
[6]https://en.wikipedia.org/wiki/Apple
[7]https://en.wikipedia.org/wiki/Schizophyllum_commune
Planning and production
Author丨Rao Gu, School of Life Sciences, Nanjing Normal University
Audit丨Zeng Hui, Director of the Institute of Edible Fungi, Fujian Academy of Agricultural Sciences
Planning丨Fu Sijia
Editor-in-charge丨Yinuo
Reviewer丨Xu Lai, Lin Lin