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Artificial cultivation of true morels: current state, issues and perspectives
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DOI: 10.1080/07388551.2017.1333082
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Critical Reviews in Biotechnology
ISSN: 0738-8551 (Print) 1549-7801 (Online) Journal homepage: http://www.tandfonline.com/loi/ibty20
Artificial cultivation of true morels: current state,
issues and perspectives
Qizheng Liu, Husheng Ma, Ya Zhang & Caihong Dong
To cite this article: Qizheng Liu, Husheng Ma, Ya Zhang & Caihong Dong (2017): Artificial
cultivation of true morels: current state, issues and perspectives, Critical Reviews in Biotechnology,
DOI: 10.1080/07388551.2017.1333082
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Download by: [Institute of Microbiology], [CH Dong]
Date: 06 June 2017, At: 20:53
CRITICAL REVIEWS IN BIOTECHNOLOGY, 2017
https://doi.org/10.1080/07388551.2017.1333082
REVIEW ARTICLE
Artificial cultivation of true morels: current state, issues and perspectives
Qizheng Liua, Husheng Mab, Ya Zhangc and Caihong Donga
a
State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China; bGuangxi Institute of
Botany, Guangxi Zhuangzu Autonomous Region and the Chinese Academy of Sciences, Guiling, China; cSichuan Province Delilong
Agricultural Technology Co. Ltd., Chengdu, China
ABSTRACT
ARTICLE HISTORY
Morels (Morchella, Ascomycota), which are some of the most highly prized edible and medicinal
mushrooms, are of great economic and scientific value. Morel cultivation has been a research
focus worldwide for more than 100 years, and the outdoor cultivation of morels has succeeded
and expanded to a large scale in China in recent years. In this study, we review the progress in
recent research regarding the life cycle and reproductive systems in the genus Morchella and
the current state of outdoor cultivation. Sclerotia formation and conidia production are two
important phases during the life cycle. The morel species cultivated commercially in America is
M. rufobrunnea based on molecular phylogenetic analysis. The species currently cultivated in
China are black morels, including M. importuna, M. sextalata and M. eximia. The field cultivation
of morels expanded in the majority of the provinces in China with a yield of fresh morels of
0–7620 kg per ha. The key techniques include spawn production, land preparation and spawning,
the addition of exogenous nutrition, fruiting management and harvesting. The application of
exogenous nutrition is the most important breakthrough in the field of morel cultivation, but
the mechanism remains unclear. It was estimated that the total amount of field cultivated fresh
morels was 500 t in 2015–2016. We also discuss the potential issues remaining in the current
literature and suggest directions for future studies.
Received 3 February 2017
Revised 24 April 2017
Accepted 25 April 2017
Introduction
True morels (Morchella spp.) are commercially important
edible mushrooms with a delicate taste and a unique
appearance, belonging to Ascomycota, Pezizomycetes,
Pezizales, Morchellaceae, and Morchella Dill. ex Pers [1].
All species in this genus are edible [2]. Morels are
among the most sought after edible fungi in world markets with a premium demanded by suppliers, and paid
by consumers [3]. Morels are the most prized and popular mushrooms in most of Europe and North America.
Morel products were very early approved by the US
Food and Drug Administration (FDA) [4]. In China, morels have been recorded in the prestigious pharmaceutical text “Compendium of Materia Medica,” which was
written by Li Shizhen during the Ming Dynasty of China,
and used to treat a variety of stomach problems. Morels
are commonly referred to as “Guchhi” in the Indian market and are some of the most important fungi from economic, social and ethno-mycological perspectives in the
Northwest Himalayan range [5].
Recent studies have demonstrated that morels
can be used to treat a wide range of conditions based
KEYWORDS
Artificial cultivation; morel;
outdoor; exogenous
nutrition; Morchella
importuna; life cycle
on their antitumor and immunomodulatory activities
[6,7], anti-inflammatory effects [8], neuroprotective
effects [9], antioxidant activity [10], and hepatoprotective activity [11].
The economic value of morel mushrooms have been
notably realized worldwide. Large crops of wild morels
are harvested in China, India, Pakistan, Turkey, and
North America [12]. Morels are some of the more valuable special forest products in Western North America,
and the annual commerce related to morels likely
ranges from $5 million to $10 million in this region [12].
In China, the annual export of dried morels increased
five-fold from 181,000 kg to 900,000 kg during the past
5 years, averaging $160 US dollars per kg [13]. In India,
morels from the Himalayas are approximately Rs
14,000–15,000 per kg [14].
Some morel species fruit in post-fire habitats. These
fire-adapted species, which are termed as “burn morels”
[15], proliferate mainly in coniferous forests following a
wildfire during spring or summer, typically for 1 or
2 years [13]. To date, there are four obligate fireadapted species, M. tomentosa, M. sextelata, M. eximia
CONTACT Caihong Dong
dongch@im.ac.cn
State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, NO.3 1st
Beichen West Road, Chaoyang District, Beijing 100101, China
ß 2017 Informa UK Limited, trading as Taylor & Francis Group
2
Q. LIU ET AL.
(treated as M. septimelata in Kuo et al. [16]) and Mel-8,
collected on burned sites, and two facultative fireadapted species, M. exuberans (discussed as M. capitata
in Kuo et al. [16]) and M. importuna, collected on
burned and non-burned sites [13]. The majority of the
commercial harvest in western North America comprises burn morels collected in the first year following
forest fires [12]. In California, members of several Native
American tribes historically collected burn morels for
food, and some tribal members continue to collect
post-fire morels [17].
In nature, the fresh morel mushroom season is very
short, and they are typically found in the markets for
only a few weeks, mainly in the spring. In addition, the
accumulation of heavy metals in the ascocarps that are
picked from natural habitats has been reported [18,19].
The unique culinary flavor and rarity, profound bioactivities, short market fruiting season and heavy metal
accumulation of wild morels have resulted in the need
to develop a biotechnological process in order to cultivate morels under controlled conditions.
Because of their complex life cycle and the lack of
knowledge surrounding ascocarp formation, these delicacies are not artificially cultivated, and the successful
cultivation of morels remains a rare and difficult task
despite more than 100 years of effort [20]. However, in
recent years, the outdoor artificial cultivation of morel
mushrooms has been rapidly developed in China. This
review will introduce the progress in research regarding
the life cycle and artificial cultivation of morels and critically discusses the issues in making these prized edible
fungi a benefit all humankind. This review provides a
summary of current knowledge and is a basis for future
research into morel cultivation.
Life cycle of morels and reproductive systems
The life cycle and reproductive systems of morels are
critical for their artificial cultivation. Morels are ascomycetes, which have both asexual and sexual reproductive
phases. Each morel ascocarp consists of numerous asci,
and each ascus contains eight spores. Volk and Leonard
[21] produced their representation of the Morchella life
cycle based on cytological observations (Figure 1),
which has been recognized to date. Sclerotia formation
and conidia production are two important phases during the life cycle (Figures 2 and 3). The primary mycelium germinated from the ejected ascospores can form
sclerotia to survive adverse conditions, such as winter
(Path 1). In the spring, sclerotia may germinate carpogenically to form a fruit body or myceliogenically to
develop a new primary mycelium. If a primary mycelium
meets another compatible primary mycelium, the two
hyphae fuze to form a heterokaryon with paired nuclei
(Path 2) [22]. This heterokaryotic mycelium may also
form sclerotia for overwintering. In the spring, these
sclerotia presumably also have the following two
options for germination: myceliogenic or carpogenic.
Two flaws are noted in this life cycle. The first is that
no evidence of sclerotia germinating to produce primordial is available to date. Fungal sclerotia are hard subterranean structures that are believed to act as a resting
stage, which is resistant to unfavorable environmental
or physiological conditions [23]. Morel sclerotia are
actually pseudosclerotia, which form from the repeated
branching and enlargement of either terminal primary
(homokaryotic) or secondary (heterokaryotic) hyphae
(Figure 2) [22]. However, morel sclerotia are also
believed to enhance survival overwinter [21], but the
conditions that trigger ascocarp formation arising from
sclerotia are not clearly understood. The other flaw concerns the conidia. During the outdoor cultivation of
morels, “powdery mildew,” which appear to be the conidia (Figure 3), is a necessary stage. However, the conidia cannot germinate under experimental conditions,
and limited conidia production is noted in laboratory
cultures [24]. The function of conidia during the life
cycle remains puzzling.
Alvarado-Castillo et al. [25] provided another theoretical life cycle of this genus that included the formation
of the conidia, chlamydospores, an imperfect phase and
sclerotia, which was complemented by genetic plasticity
and a possible capacity for haploid meiosis. However,
this life cycle is theoretical and has yet to be verified.
The reproduction mode of morels has been debated
by some researchers. Several studies have indicated
that species in the Elata and Esculenta clades of
Morchella might be heterothallic and could outcross in
nature [22,26,27]. However, Yoon et al. [28] reported
that the species in the M. esculenta complex (Esculenta
Clade) were haploid because no heterozygosity was
found, which is similar to the results observed in Mel-13
and M. eohespera [29]. It is hypothesized that selfing
might be very common in these morel species or that
they were homothallic, and their fruiting bodies were
developed from haploid mycelia. Dalgleish and
Jacobson [30] hypothesized the high inbreeding potential of M. esculenta. The recent study concluded that the
mating systems of morel species remains uncharacterized [29].
Development of morel artificial cultivation
For centuries, various methods of morel cultivation
have been attempted. The first report of the outdoor
cultivation of morels occurred in France in 1882 in
CRITICAL REVIEWS IN BIOTECHNOLOGY
3
Figure 1. Morchella life cycle proposed by Volk and Leonard [21].
Figure 2. Morel sclerotia grown under artificial conditions (in this laboratory). (A) Sclerotia production in a PDA medium in a
plate (bar ¼1 cm). (B) Sclerotia morphology under an anatomical lens (bar ¼500 lm).
association with Jerusalem artichokes and was reported
by Roze [31]. In 1904, Molliard claimed to have cultivated morels in an apple compost. However, there was
no evidence demonstrating that they were actually
responsible for the morels that grew, i.e. the morels
may have arisen naturally [3].
In 1982, Ower [32] reported the successful cultivation
of Morchella, and its life cycle was replicated in the
4
Q. LIU ET AL.
Figure 3. Powdery mildew and conidia in the outdoor cultivation of M. importuna (in this laboratory). (A) Powdery mildew in the
soil. (B) Conidia (bar ¼10 lm).
mycology laboratories of San Francisco State University,
which produced a typical ascocarp in a walk-in growth
chamber. Then, three patents (US Patents 4594809,
4757640, and 4866878) were issued from 1986 to 1989
for morel cultivation to Ower et al. [33–35]. Their work
revealed the optimal temperature, humidity and ventilation for morel cultivation. The key process described in
their patents is an inoculation with the morel’s sclerotia.
Their work was a tremendous breakthrough in the
“dream” of morel cultivation. After several more transfers of cultivation rights and associated corporate mergers, morel cultivation has resurfaced at “Diversified
Natural Products” (DNP, currently named Gourmet
Mushrooms Inc.) Mason County, MI, USA [12]. This company started selling fresh morels in 2005 [12]. In 2008,
the indoor cultivation of morels in America was abandoned thoroughly due to the reduction of output and
the bacterial contamination [36].
Later, Stewart C. Miller obtained a patent in 2005 (US
Patent 6907691B2) by constructing ectomycorrhizal
symbiosis between Morchella mycelium and tree seedlings [37]. Masaphy [20] reported the successful initiation and development of the M. rufobrunnea fruit body
via a soilless-controlled process in laboratory-scale
experiments. This technique made indoor-cultivation of
morels possible but has not been transferred to scaledup industrial morel farming.
These experiences promoted research on techniques
for the artificial cultivation of morels. Since the 1980s,
numerous scientists in China started to focus their
research studies on morel cultivation. The first patent
was applied in 1993 based on the successful fruiting of
artificially cultivated M. esculenta [38]. However, this
technique is limited given its poor stability and reproducibility, requiring further work for realizing techniques for practical morel production. The bionic
cultivation of morels based on the Populus bonatii and
crop straw succeeded in 2002 and was commercialized
in Yunnan Province in 2004 [39,40]. The largest scale is
33 ha per year with a morel yield of 450–3000 kg per ha
[40]. However, this technique is limited due to wood
consumption.
The most important progress in morel cultivation in
China is the invention and application of an exogenous nutrition bag, which made an important breakthrough in the field cultivation of morels. In fact, the
idea of exogenous nutrition initially originated from
Ower’s patent. R. D. Ower was honored as the “Father
of Morels” by some Chinese scholars. In 2000, scientists from the Sichuan Academy of Forestry obtained
the fruit body of a morel in a flowerpot grown outside
their door when exogenous nutrition was supplied
[36]. The followed studies demonstrated that the
exogenous nutrition supply is important for the outdoor cultivation of morels. In 2011, the scale cultivation of morels in the field began with 200 ha and
expanded quickly to 1600 ha in 2016 according to a
recent Chinese survey [41].
CRITICAL REVIEWS IN BIOTECHNOLOGY
5
Figure 4. Morel species cultivated in China: M. importuna (A), M. sextalata (B) and M. eximia (C).
Current states of morel cultivation
Morel species currently under cultivation
According to the latest information contained in the
Index Fungorum [42], 323 terms related to Morchella
have been reported (including species, subspecies,
and varieties). Phylogenetic analyzes identified 65
species within Morchella, including the following
three lineages: a basal monotypic lineage represented
by M. rufobrunnea (Rufobrunnea Clade, two species)
and two sister clades comprising black (Elata Clade,
36 species) and yellow morels (Esculenta Clade, 27
species) [43].
Although the cultivation reported in 1982 was
based on one species (M. esculenta Fr. sensu Groves
& Hoare [32]), the patents claim that the methods
apply to all Morchella species [33–35]. Kuo [44] suggested that the species cultivated by Ower (and subsequently by others) was M. rufobrunnea according to
the photographs, and the morels cultivated by
Diversified Natural Products also match M. rufobrunnea after examination.
The species currently cultivated in China include M.
importuna [29,45–48], M. sextelata [46–48], and M. eximia [46,47] (Figure 4). Identification of the cultivated
morels was based on morphological characters and
molecular evidence [46,47]. These species all belong to
black morels. M. importuna accounted for 80–90% of
the cultivated area [47]. “Sichuan Morel No.1” (M. importuna, strain SCYDJ1-A1) was the first variety approved in
China. Morchella conica can also be cultivated [39].
Whether other species of Morchella can be cultivated is
currently unknown and deserves further research.
n & F. Tapia
Morchella rufobrunnea Guzma
Morchella rufobrunnea and M. anatolica comprise a separate evolutionary lineage, Rufobrunnea Clade, from the
Esculenta and Elata clades [49]. Morchella rufobrunnea is
easily distinguished on the basis of “its abruptly conical
6
Q. LIU ET AL.
young cap with pale ridges and nearly black pits, and
its rufescence” [44]. Morchella. rufobrunnea appears in
woodchips and landscaping settings on the West Coast
from California to Seattle in USA [16].
Molecular phylogenetic analysis confirms that
M. rufobrunnea is the morel cultivated commercially in
USA [16,44]. This finding suggests a saprotrophic role
for this species. In 2010, Masaphy in Israel reported a
successful M. rufobrunnea fruiting body initiation and
development in laboratory-scale experiments [20]. This
laboratory-scale technique makes indoor cultivation of
morel possible but has not been transferred to scale-up
industrial morel farming.
Morchella importuna M. Kuo, O’Donnell & T.J.
Volk
Morchella importuna, M. sextelata and M. septimelata
(termed as M. eximia in 2015 [50]) are three black morels from North America described in 2012 [16].
Morchella importuna corresponds to the phylogenetic
species Mel-10 in O’Donnell et al. [51]. The species is
distinguished from other morels on the basis of its
regular laddered, vertically oriented pits and ridges [16].
This species occurs in gardens, woodchip beds, and
other urban settings of northern California and the
Pacific Northwest region of USA and Canada [16]. The
fungus has also been reported in Turkey, Spain, France,
Switzerland, and China [50–53].
The first morel variety approved in China, M.
importuna strain SCYDJ1-A1, was derived from a wildcollected mushroom in eastern Tibetan Plateau and was
domesticated by a research group in the Soil and
Fertilizer Institute, Sichuan Academy of Agricultural
Sciences, China [54]. Morchella importuna appears to be
a facultative post-fire species given that it has been collected from non-burned sites in Yunnan, China,
Germany, and Turkey [50–54]. Its saprophytic life style
contrasts the ectomycorrhizal life style of numerous
other species of Morchella, for which associations and
interactions with plants are often essential at certain
stages.
Morchella sextelata M. Kuo
Morchella sextelata corresponds to the phylogenetic
species Mel-6 in O’Donnell et al. [51]. This species has
been collected in Western North America, Mexico and
Yunnan, China [16,53] and is found at 1000–1500 m in
lightly to moderately burned conifer forests. Morchella
sextelata is often found primarily in years immediately
following forest fires [16]. From a strictly morphological
perspective, the species is virtually identical to several
members of the Elata Clade (M. eximia, M. brunnea,
M. angusticeps, and M. septentrionalis). However,
because it is apparently limited to conifer burn sites,
it can be easily separated from all species but M.
eximia [16].
Morchella sextelata has also been domesticated,
bred and commercially developed in China. The original
strain was isolated from the Aba area in northern
Sichuan, China [47], and the cultivation area for this
morel variety reached 67 ha in 2015 [48].
Morchella eximia boud.
Morchella septimelata is a species of fungus in the
Morchellaceae family described as new to science in
2012 by Kuo et al. [16]. In 2015, Richard et al. [50] clarified the taxonomic status of this species, retaining the
name M. eximia rather than M. septimelata. M. eximia
corresponds to phylogenetic species Mel-7 in O’Donnell
et al. [51]. Based on present data, the species can
only be reliably distinguished from M. sextelata via DNA
analysis [16]. Morchella eximia has been found in North
America [50], Europe, Turkey [52], China [53], and
Australia [50], appearing at 1000–2000 m in lightly to
moderately burned conifer forests often near creek
beds, springs and seeps [16]. This widespread post-fire
morel occasionally fruits extensively in burnt forests and
on rubble [50].
Similar to M. sextelata, M. eximia has also been
domesticated and bred in China. However, the cultivation of this species is under development, and its
market share is currently much lower than the other
two black morels [47]. The original strains were isolated
in Yunnan and Sichuan provinces [53].
Scale of morel cultivation in china
The area in China under morel cultivation has expanded
rapidly from 200 ha in 2011 to more than 1200 ha in
2015 [55]. The area is estimated to reach 1600 ha in
2016 [41]. Morel cultivation has expanded in the majority of provinces in China, particularly in Sichuan,
Chongqing, Yunnan, Hubei, Shanxi, Henan, and
Guizhou. The field cultivation yield of fresh morels is
0–7620 kg per ha [40], with common yields of
0–3000 kg per ha and significant differences are noted
[56]. The total amount of field cultivated fresh morels
was estimated to be 500 t in 2015–2016.
After the successful outdoor cultivation of morels,
many growers began to attempt indoor cultivation and
industrialized production. However, to date, indoor cultivation has not been successful.
CRITICAL REVIEWS IN BIOTECHNOLOGY
7
Figure 5. Morels cultivated in farmland (A) and forest farming (B).
Key techniques in the field cultivation of morels
The artificial cultivation of morels has attracted an
increasing number of farmers and is receiving the
enthusiastic support of governmental organizations and
policies in China. To date, the cultivation in farmlands
and forest farming are the main morel cultivation patterns in China (Figure 5). Cultivation can be performed
in various terrains, including plain-hills zones, plateau
zones, and mountain zones. Given that dim light is
needed and direct sunlight is harmful to the growth of
morels, a canopy is necessary. The cultivation process
includes spawn production, land preparation and
spawning, an exogenous nutrition supply, fruiting management and harvesting.
Spawn production
The quality of the spawn is the most important factor
for the cultivation of any mushroom. Similar to the cultivation of numerous other mushrooms [57], the starter
culture (or mother culture), mother spawn and final
spawn are used for morel cultivation (Figure 6). The
starter culture can be made from fresh and healthy fruit
bodies of morels or obtained from a spawn producer or
a laboratory. More agar cultures are then made from
this starter culture. These cultures serve to inoculate
larger containers (bottles or bags), which can be used
to inoculate the final spawn substrate.
The medium used for the morel starter culture is typically potato dextrose agar (PDA) or PDA with humus.
The same or a similar substrate can be used for the
mother spawn and the final spawn. The most-widely
used raw substrate materials include: sawdust, wheat,
wheat bran, quicklime and humus. The following recipe
can be used: wheat 46%, husk 20%, wheat bran 18%,
sawdust 10%, gypsum 1%, precipitated calcium carbonate (PCC) 1%, and humus 4% [55].
Glass or heat-resistant plastic bottles are often used
for the mother spawn, and heat-resistant bags are used
for the final spawn for convenient transportation.
Approximately 4500 bags (14 28 cm) of the final
spawn (3000–3375 kg) are used per ha. Numerous
spawn producers have recently emerged in China,
and the majority of morel growers directly purchased
the final spawns. The cost of the spawn is
52,500–75,000 RMB per ha (US$7620-10880).
Spawning
Morels are aerobic, and loose soil is good for their
growth. Soil plowing and removing sundries, such as
rocks, are necessary before spawning (Figure 7(A)).
Occasionally, quicklime can be used in soil to kill some
pests and adjust the pH [58]. The mushroom bed
should be 80–150 cm wide and 15 cm deep. The distance between the neighboring beds is 30 cm.
The spawning for morel cultivation is different from
that for most mushrooms given that the morel spawn is
sown directly into the cropland or forest, which is similar to the seeding of wheat crops (Figure 7(B)). The season for morel spawning changes based on the different
elevations and is mainly from October to the middle of
December. Spawning typically begins when the highest
local temperature is <20 C. The soil humidity is maintained at 50–70%. Both sowing in trenches and strewing are used.
Nonnutritive casing soil is spread over the spawn
evenly after spawning at a depth of 3–5 cm. Film
mulching and a canopy can help maintain the temperature, humidity, and dim sunlight.
Exogenous nutrition aiding
The morel mycelia are colonized in the soil after the
spawning under suitable temperature and humidity, i.e.
<20 C and 50–70% soil humidity. After 10–15 d, a vast
expanse of whiteness appears on the surface of the
mushroom bed, which is called a “powdery mildew”
(Figure 3(A)). In actuality, this white area is the morel
mycelia and conidia that are produced on the soil
(Figure 3(B)).
8
Q. LIU ET AL.
Figure 6. Spawn used for morel cultivation (in this laboratory). (A) Starter culture (or mother culture). (B) Mother spawn. (C) Final
spawn.
Then, an exogenous nutrition bag can be placed in
the mushroom bed. The substrates used for the
exogenous nutrition bag include wheat, chaff, sawdust, and cottonseed hull. The same recipe can be
used as the final spawn, and some recipes are provided in many Chinese patents [59,60], e.g. wheat
67%, sawdust 28%, and lime 5% [59]. The composition of exogenous nutrition does not appear to be
very strict. The exogenous nutrition bag is filled with
a heat-resistant plastic bag and is subsequently sterilized. Holes or a large cut on one side of the bag
should be made, and the bag is placed tightly in the
mushroom bed (Figure 7(C)).
An 50-cm interval is maintained between each
bag, and 22,500–30,000 bags per ha were placed.
Under suitable temperature and humidity, morel
mycelia will grow using the added nutrition and
become full of the nutrition bag after 15–20 d.
The bags can be removed when the nutrition bag is
depleted, which occurs after 40–45 d. Exogenous
nutrition aiding is necessary for the ascomata
development of morels under the current technique.
However, the mechanism remains unknown.
Fruiting management
The most important environmental factor during morel
cultivation is soil moisture and air humidity. Micro-spray
irrigation is necessary for morel cultivation. Timely
draining of rain water and supplementing water during
drought should be performed. The humidity of the soil
surface should be maintained at >50%.
Before fruiting, the soil and air humidity should
be increased. When the temperature increases to
6–8 C in the spring, the trench between the beds
should be slowly flooded to maintain the air
humidity at 85–90% and the soil moisture at 65–75%.
These conditions will stimulate the differentiation of
the primordium of the morels. Cotter [61] also found that
flooding is necessary for the outdoor cultivation of morels, and flooding stimulates the morels to feed on beneficial bacteria that are essential for fruiting. However, the
flooding mechanism remains to be studied.
CRITICAL REVIEWS IN BIOTECHNOLOGY
9
Figure 7. The process of morel cultivation in the field. (A) Soil plowing. (B) Spawning and casing. (C) Exogenous nutrition aiding.
(D) Primordium. (E) Nascent fruit body. (F) Mature fruit body.
Temperature is also important for morel cultivation.
The optimal temperature for primordium differentiation
is 6–10 C. Diurnal temperature variations >10 C stimulate primordium differentiation. Morel fruit bodies cannot grow well at temperatures >20 C. However, the
temperature can only be adjusted by film mulching, a
canopy, and spraying and ventilating in outdoor
cultivation.
Another important management technique during
morel cultivation is pest control. Competitive contaminants include: Trichoderma, Aspergillus, Rhizopus, Mucor,
Neurospora, Coprinus and bacteria [62]. Common insects
include: Limax, mites, spring tail and maggot. All chemical pesticides are absolutely prohibited, but physical
and biological control techniques can be used.
Issues and perspectives
Harvesting
Life cycle and reproductive systems
When the ascocarp grows to 10–15 cm with an obvious
ridge and sinus, the fruit body can be harvested. Fruit
bodies can be dried at a low temperature.
Determining the life cycle and reproductive systems of
Morchella will contribute to the understanding of sclerotia formation and ascocarp production. As Volk [63]
True morels are highly prized for their medicinal and
nutritional values and are intensively collected around
the world by mycophiles. Although outdoor artificial
cultivation has been successful in China, knowledge
regarding the factors controlling fruit body initiation
and development remains far from sufficient. Along
with the rapid expansion of morel artificial cultivation in
China, several notable problems, including spawn aging
and mechanisms of exogenous nutrition, are frustrating
to morel farmers. The enhancement of biological
research will be helpful for solving those problems and
promoting technology for the development of artificial
cultivation.
10
Q. LIU ET AL.
clearly indicated, morels have a complex life cycle that
complicates the process of scaling up cultivation methods to efficient commercial procedures. Although
numerous studies have been performed on the life
cycle, the information to date is limited and
inconclusive.
Conidia production seems to be necessary during
outdoor cultivation (Figure 3). However, in pure culture
under various conditions, no conidia production is
observed [24]. The conidia produced during outdoor
cultivation basically cannot germinate [64]. The mechanism by which morels produce the conidia and its
function are puzzling.
Morels appear to require the intermediate stage of
sclerotia formation [33–35,63] before they produce fruit.
Stott and Mohammed [3] and Winder [65] asserted that
growth substrates and their nutritional composition
affected mycelial characteristics and sclerotia formation.
The presence of a sclerotial stage in morels may be a
precursor for ascocarp formation but could also simply
be a nutrient storage organ awaiting favorable conditions for ascocarp production. During outdoor cultivation in China, it is not clear whether sclerotia formation
is necessary for fruit body development.
Sequencing morel genomes will provide unprecedented insights into fruiting-related genes, the mating
system and genes essential for the sexual reproduction of morels. To date, the genome of only two species in the Elata Clade (M. importuna and M. conica)
has been completed and reported in the 1000 Fungal
Genomes project supported by the DOE Joint
Genome Institute [54].
Trophic mode of morels
The trophic mode of morels has been a source of scientific interest and debate for a long time. It is suggested
that morels form an association with tree roots in stable
ecosystems [66]. A study on the muffs formed by M.
rotunda strongly indicates that M. rotunda can form a
symbiotic relationship with plant roots, but the role of
this symbiosis in the morel life cycle is unknown [67]. In
laboratory isolates, M. elata form ectomycorrhizal structures (mantle and Hartig net) with Larix occidentalis
(larch), Pinus contorta (lodgepole pine), Pinus ponderosa
(ponderosa pine), and Pseudotsuga menziesii (Douglasfir) but not with Arbutus menziesii (madrone) [68]. Stark
et al. [69] hypothesized that morels were associated
with orchids based on evidence obtained through a direct PCR amplification of root-extracted DNA and the
cloning of the PCR products.
By examining the relative abundance of the stable
isotopes, Hobbie et al. [70] suggested that morels were
largely saprophytic, whereas Li et al. [71] suggested that
morels with black pilei were saprophytic and that those
with yellow pilei were mycorrhizal. Baynes et al. [72]
studied Morchella, an endophyte in the aboveground
stem tissue of cheat grass, and reported that M.
sextelata could infect cheat grass roots. Although M.
sextelata and M. eximia were reported as obligate fireadapted species [53], they occasionally fruit extensively
in burnt forests and on rubble [16]. Successful cultivation in the field suggested that at least M. importuna, M.
sextelata, and M. eximia were saprophytic species, but
how ascomata development was triggered remains
unclear. A recent study also concluded that morels fruiting in post-fire environments were saprotrophic using
isotopic analysis [73]. To date, the trophic strategies of
Morchella have not been consistent, but the available
data seem to indicate that Morchella likely includes not
only saprophytic species and mycorrhizal species but
also facultative mycorrhizal species. This relationship
does not imply that an ectomycorrhizal relationship is
essential for either the morel life cycle or ascocarp production. More research in this area is needed to confirm
such a relationship.
Spawn quality
Spawn quality is a key for almost all mushroom cultivation. The cultural morphology of Morchella isolation
in different growing media is random and unstable
[74,75], which highlights the difficulty in spawn
quality evaluation. Currently, no quality standard is
available for morel spawns in China, and growers
empirically judge the quality exclusively based on the
quantity of sclerotia. In fact, the relationship between
sclerotia and ascocarp production has not been
determined. The insufficient knowledge regarding
morel biology, including genetics and life cycle, has
resulted in many unsolved problems regarding its
spawn.
On the other hand, morel strains senesce quickly,
losing their vigor and viability; thus, strains must be
repeatedly reselected from spore cultures [76]. The
application of the senesced spawns characterized by
slim mycelia, reduced growth rate and untidy growth
during the cultivation may result in a remarkable
reduction in production. Unfortunately, aging in
Morchella mushrooms has not been systematically
studied.
Producers must take effective measures to store the
spawn, which can preserve the spawn’s vigor and viability, and an inappropriate storing method may accelerate the spawn’s senescence or even contaminate it.
Research regarding how to effectively preserve morel
CRITICAL REVIEWS IN BIOTECHNOLOGY
spawns in China is lacking, and more attention should
be given to this topic.
11
Scientific and Technological Project in Shanxi Province
(FT2014-03-01) and the Key Research and Development
Program from Government of Guangxi Zhuangzu
Autonomous Region (2016AB05317).
Mechanism of exogenous nutrition
Exogenous nutrition supply is a critical technique for
the successful outdoor cultivation of morels, but the
mechanism underlying the exogenous nutrition remains
unclear. The words “exogenous nutrition” initially
appeared in Ower’s patent [35]. This researcher suggested that alterations from a nutrient-rich to a nutrient-poor environment will induce the fungus to enter
the sexual growth cycle in which ascocarps are produced. The majority of morel growers in China believe
that the exogenous nutrition bag supplies the nutrition
for mycelia growth [40]. Radiolabeling could be useful
for answering this question.
Morel cultivation using the current technique is
extremely labor intensive. Exogenous nutrition supply
increases the labor and cost given that making the
exogenous nutrition, sterilizing it and placing it in the
mushroom bed require a significant amount of labor.
Therefore, the mechanization of the exogenous nutrition supply or another cultivation mode will serve as
other targets based on the mechanism of the exogenous nutrition.
Indoor and industrial cultivation
Mushroom farming is and will continue to move
towards large-scale industrialization. Morel cultivation
in the field and forest has expanded rapidly in China.
However, there is a great risk given that outdoor cultivation is strongly affected by the climate and soil, e.g.
the intensive low temperature and cold wave in 2016
caused great losses for morel growers [36]. The indoor
cultivation of morels in America was completely abandoned in 2008, and indoor cultivation on a large scale is
not currently being performed. Techniques for the
indoor cultivation of morels will be the research focus
for the coming years, and we believe that it will succeed
within a couple years based on the detailed biological
research on morels.
ORCID
Caihong Dong
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Disclosure statement
No potential conflict of interest was reported by the
authors.
Funding
This study was funded by the National Basic Research
Program of China (2014CB138302), the Coal-Based Key
http://orcid.org/0000-0002-2558-3404
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