全 文 ：
菌物学报
jwxt@im.ac.cn 22 November 2016, 35(11): 1375‐1386
Http://journals.im.ac.cn Mycosystema ISSN1672‐6472 CN11‐5180/Q
Tel: +86‐10‐64807521 Copyright © 2016 Institute of Microbiology, CAS. All rights reserved.
研究论文 Research paper DOI: 10.13346/j.mycosystema.150232
Supported by TTI Green genetics (TTI06201), Wageningen UR‐Plant Breeding, C4C Holding, Sylvan, Dutch Product Board for
Horticulture, the Greenery, Banken Mushrooms, WeBe Engineering and National Basic Research Program of China (2014CB138305).
*Corresponding author. E‐mail: gaowei01@caas.cn; Tel: +86‐10‐82108761; Fax: +86‐10‐82106207
Received: 2015‐11‐11, accepted: 2016‐01‐08
Effects of environmental factors on bruising sensitivity of button
mushrooms (Agaricus bisporus)
GAO Wei1, 2* BAARS Johan JP1 DOLSTRA Oene1 VISSER Richard GF1 ZHANG Jin‐Xia2
SONNENBERG Anton SM1
1Plant Breeding, Wageningen University and Research Center, 6700AA Wageningen, the Netherlands
2Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China
Abstract: White button mushrooms are fragile and discolor soon after mechanical bruising. This hampers the development of
mechanical harvesting for button mushrooms and causes loss of postharvest quality. The extent of discoloration can be affected
by environmental conditions. A factorial design analysis was conducted to screen the effect of factors influencing the bruising
sensitivity of button mushrooms, and to find out a combination of environmental factors generating the largest variation among
bruising sensitive and bruising resistant strains. In this way a maximal variation of the trait ‘bruising sensitivity’ can be induced in
segregating populations intended to map this trait. Three environmental factors were investigated on four genotypes (strains),
i.e., thickness of the casing layer (2.5cm and 5cm), wetness of casing (dry and normal), and relative humidity in the growing
room (80% and 87%). Analysis of variance (ANOVA) showed that genotype (strain) was a significant factor influencing bruising
sensitivity as well as casing thickness. Significant factor interaction effects were observed. The factor combination generating the
largest difference in bruising sensitivity between the four strains was identified, i.e., a thickness of the casing layer of 5cm,
normal humidity of the casing, and 87% for relative humidity in the growing room.
Key words: Agaricus bisporus, bruising sensitivity, environmental factors, relative humidity, casing wetness, thickness of casing layer
环境因子对双孢蘑菇损伤敏感性的影响
高巍 1, 2* BAARS Johan JP1 DOLSTRA Oene1 VISSER Richard GF1 张金霞 2
SONNENBERG Anton SM1
1Plant Breeding, Wageningen University and Research center, 6700AA Wageningen, the Netherlands
2中国农业科学院农业资源与农业区划研究所 北京 100081
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摘 要：在机械损伤过程中，白色双孢蘑菇极易被损伤并迅速褐变，使得机械采收的鲜菇质量低下，并且影响机械采收
技术的应用和发展。机械采收双孢蘑菇的褐变程度（损伤敏感性）受栽培环境条件的影响。本文应用因子设计分析的方
式研究多个因子对双孢蘑菇机械损伤敏感性的影响。以 4 个菌株为材料测试 3 个环境因子对双孢蘑菇损伤敏感性的影响，
即覆土的厚度（分为 2.5cm 和 5cm 两个水平），覆土的湿度（分为干覆土和正常覆土两个水平），以及菇房内的相对湿度
（分为 80%和 87%两个水平）。目的是找出能够在不敏感菌株和敏感菌株间产生最大敏感性差异的环境条件，由此得到的
环境条件将应用到后续的群体分离分析中以得到最大的敏感性变异率。根据方差分析结果得出基因型（菌株）和覆土厚
度是影响损伤敏感性的显著性因子，因子间相互作用显著。能够在不敏感菌株和敏感菌株间产生最大的损伤敏感性差异
的环境条件为正常湿度的 5cm 厚覆土材料和 87%的菇房内相对湿度。
关键词：双孢蘑菇，损伤敏感性，环境因子，空气相对湿度，覆土含水量，覆土厚度
INTRODUCTION
Button mushroom, Agaricus bisporus (J.E. Lange)
Imbach, is one of the most cultivated and consumed
mushrooms, especially in western countries (Chang
& Wasser 2012). Mechanical harvesting is widely
used by large mushroom producers in the world in
order to reduce the production cost. For instance,
nearly 60% of the production is harvested
mechanically in the Netherlands, and the rest is
handpicked (Straatsma et al. 2007). In practice, only
30–35kg/h can be picked by hand whereas the
capacity of the mechanical harvesting system is up
to 400 times higher than that of handpicking.
However, mechanical harvest causes damage,
especially to the mushroom caps, leading to
discoloration and reduction in quality. According to
our previous test, all present‐day white commercial
button mushroom varieties are genetically similar
(Sonnenberg et al. 2011) and sensitive to bruising
(Weijn et al. 2012). The present mechanical
harvesting system is, therefore, not suitable for the
harvest of mushrooms to supply of the fresh market
for which high‐quality standards are demanded.
Mushroom quality is judged by the consumer as
depending on a number of factors, e.g., color,
texture, cleanliness, maturity and flavor (Burton
2004). The main factors which contribute to loss in
quality after harvest are mushroom discoloration
and maturation, losses in weight and changes in
texture (Burton & Noble 1993). Since consumers
select products based on visual inspection,
discoloration of mushrooms, i.e., bruising sensitivity
is the main factor that determines mushroom quality.
Mushroom discoloration is supposed to develop as a
result of biochemical derivative processes occurring
upon senescence or mechanical bruising, which
leads to oxidation of natural phenols catalyzed by
tyrosinase. This results in products, i.e., quinones,
which chemically react with themselves and with
other constituents of the cell to form melanin;
brown cap color is due to the dark melanin (Jolivet
et al. 1998). Different mechanisms might be involved
in bruise‐induced discoloration and post‐harvest
discoloration of long term storage (Burton & Noble
1993). Many studies were conducted to dissect the
mechanism of post‐harvest discoloration on storage
conditions, enzyme activity (Li et al. 2009; Wang et
al. 2014), cellular changes (Zhu et al. 2009), and
polyphenol oxidase genes (Weijin et al. 2013) etc.
For research purposes, the level of
discoloration after mechanical damage (bruising
sensitivity) has been quantified with different
bruising devices and methods. A
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polystyrene-shaking box was first used to bruise
mushrooms, which oscillated horizontally over a
distance of 40mm at a frequency of 2Hz for 10
seconds (Noble et al. 1997), and a bruise-ometer
was then developed to deliver a slip-shear treatment
on the surface of mushrooms (Burton 2004).
Nevertheless, the bruise-ometer developed by
Burton (2004) damaged mushrooms too much for
their research purposes and did not allow a
comparison between the bruised and non-bruised
area on the same mushroom (Weijn et al. 2012).
Therefore, a different bruising device and an image
analysis system were developed to quantify bruising
sensitivity (Weijn et al. 2012). Bruising sensitivity in
all the previous studies was assessed by quantifying
discoloration with the CIE L*a*b* system
(Robertson 1990) but with different values. Noble
et al. (1997) used the b value as an indicator of
bruising sensitivity; the larger the b value the
higher the bruising sensitivity (Noble et al. 1997).
Burton (2004) on the other hand used the L value
[or loge(100-L)] as an indicator, i.e., the higher the
value the lower the bruising sensitivity (Burton
2004). Weijn et al. (2012) used an image analysis
system to quantify cap color based on whiteness
index, which is equal to L minus 3*b (Weijn et al.
2012). Whiteness index was claimed to show a
closer resemblance to the perception of the human
eye of the white color than the L value. The
bruising sensitivity was defined as the difference in
whiteness index between the non-bruised area and
bruised area.
The variation of bruising sensitivity is not only
determined by genetic factors, but also influenced
by environmental factors. Most studies since
mid-1980 have been performed on genetically
similar hybrid strains. Several environmental factors
were studied to test the influence on bruising
sensitivity, e.g., the climate conditions in the
growing room, the casing depth, the water potential
of casing, the depth of compost etc. Mushrooms of
flushes 1 & 2 grown in high humidity (92%) were less
sensitive to bruising than those grown at low
humidity (85%) (Burton 2004). Flush 2 mushrooms
were significantly less discolored after bruising than
those from flushes 1 and 3 (Burton & Noble 1993).
Compost is the substrate of mushroom production,
and it contains all nutrition needed for mushroom
growth. Experiments studying the influence of
compost on mushroom quality are scares.
Mushrooms grown on less degraded, straw-like
compost were slightly but significantly less
discolored (high L value) after bruising than those
grown on more degraded compost (Burton 2004).
Mushroom number and dry matter content were
greater on higher amounts of compost per square
meter of growing area, but difference in compost
amount had no influence on mushroom
susceptibility to bruising (Noble et al. 1997). Casing
layer supplies water for the growth and
development of mycelium and fruit bodies. Two
casing compositions, varying in content of sugar
beet lime and peat, were tested at three water
potential levels. With casing composition of 30%
sugar beet lime (70% peat), mushrooms grown in
dry casing were significantly less sensitive to bruising
than those grown in medium and wet casing (Burton
2004). Nevertheless, Flush 1 mushrooms grown in
wet casing discolored significantly less (higher L
value) than mushrooms grown in medium and dry
casing; Flush 3 mushrooms grown on dry casing
discolored less than those from medium casing and
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wet casing; Flush 2 mushrooms grown in casing of
different water potential did not show difference in
bruising sensitivity (Burton 2004). In addition,
Bruising sensitivity was also influenced by casing
depth. Mushrooms grown on deep casing (40mm
and 55mm) discolored less than shallow casing
(25mm) (Noble et al. 1997).
According to these aforementioned studies,
bruising sensitivity (BS) of button mushroom can be
influenced by multiple environmental factors. The
most important factors influencing mushroom
bruising are the wetness of casing and the humidity
in growing rooms; casing depth is in turn more
important than casing composition and compost
type (Burton 2003). Thus, there is generally a clear
picture of the factors that influence bruising
sensitivity. However, the impact of the interactions
between factors on this trait is still largely unknown.
A main objective of this study was to find for
breeding purposes a suitable combination of
environmental conditions for the evaluation and
analysis of BS. Therefore we did a multi‐factorial
study to get a better insight in the relevance of
interactions between main factors i.e., wetness of
casing, casing depth and relative humidity affecting
BS and to find a better environmental condition
generating larger BS variation.
1 MATERIALS AND METHODS
1.1 Mushroom strains
In this study four white button mushroom
strains (TO7, CH1, TW4 and TW7) were used. They
were selected based on previous research, in which
bruising sensitivity of a number of strains was
studied (Weijn et al. 2012). TO7 and CH1 were
selected as representatives of strains with low
bruising sensitivity (resistant) and TW4 & TW7 as
representatives of strains with high bruising
sensitivity (sensitive). All the four strains were
obtained from the strain collection of Wageningen
UR Plant Breeding.
1.2 Experimental design
All the four selected strains were used in a
cultivation test to explore the effects of three
environmental factors on bruising sensitivity (BS) in
four replicates. Three environmental factors tested
in this study were relative humidity (RH) in the
growing room, casing depth (CD), and wetness of
casing (CW). Each environmental factor had two
levels (Table 1). The dry and normal casing soils
(different in wetness) were obtained from a
commercial company (CNC Grondstoffen, Milsbeek).
The water content of casing were measured as 77%
(W/W) for the dry casing and 79% (W/W) the normal
casing, respectively. The RH in the growing rooms
during the production phase was set at 80% and 87%,
respectively. Thus, 23 environmental factor
combinations were tested on four strains
(genotypes), resulting in a total of 32 treatments
[strain (4)* RH (2)* casing depth (2)* types of casing
(2)]. Each treatment was replicated in four times
(trays). This implies that a total of 128 trays were
divided over two growing rooms that differed in RH.
The trays within each room were randomized.
Table 1 Levels of environmental factors
Level Factor
Relative
humidity
Casing
depth
Wetness of
casing*
1 0.80 2.5cm Dry (77%)
2 0.87 5.0cm Normal (79%)
Note: *, in brackets water content of casing soil.
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1.3 Spawn preparation and mushroom cultivation
Spawn of the four strains used in this study was
prepared in polypropylene boxes with an air filter
(280mL, OS60+ODS60, Combiness, Eke, Belgium). To
fill the 128 spawn boxes, 6kg sorghum grains were
boiled for 20min in 10L tap water. After draining of
excess water and cooling down in the open air, the
cooked sorghum grains were mixed with 2.4% (W/W)
gypsum and 0.7% (W/W) lime. Each box was filled
with 80g cooked sorghum and sterilized at 121°C for
20min. A piece of mycelial inoculate (3cm2 per box)
of one of the four strains, pre‐grown on MMP plates
[1% (W/W) malt extract, 0.5% mycological peptone,
10mmol/L MOPS, and 1.75% agar, pH 7.0] was
inoculated in each spawn box. Spawn colonized
within two weeks. To achieve even colonization, the
spawn was shaken one week after inoculation and a
second time three days later.
Commercial phase II mushroom compost
(16kg/tray, CNC Grondstoffen, Milsbeek) was filled in
128 trays (56cm×36cm×20cm) and each tray was
subsequently inoculated with a single box of
sorghum spawn (around 110mL). Two subsets of
trays were distributed randomly over the growing
rooms having either a RH of 80% or 87%. After 16
days of spawn run (air temperature 21–23°C aimed
at keeping compost temperature near 25°C; RH 95%;
CO2 0.35%), the difference between trays in casing
type (of different water content) and in depth of
casing soil (CNC Grondstoffen, Milsbeek) were
established. Casing colonization was performed
under the same climate conditions as used for
spawn run. Casing soil was ruffled. After 3 days of
recovery growth, the room was vented at a rate of
0.075°C/h until the air temperature reached 18°C.
Meanwhile, the level of CO2 was lowered to
0.1% at a speed of 0.0035%/min. The RH of one
room was set at 80%, and that of the other room
was set at 87%. Since different depths and types of
casing need different time lengths for mycelium
colonization and different amount of irrigation
water, casing application and irrigation before the
first flush were scheduled (Supplementary file 1).
Casing of 2.5cm was applied one week later than
the 5cm casing in order to have a coherent
cropping time. The total amount of water for
irrigation before the first cropping flush was also
different for different treatments, i.e., 11.25L/m2
for normal 5cm casing, 7L/m2 for dry 5cm casing,
1.5L/m2 for normal 2.5cm casing, and 0.25L/m2 for
dry 2.5cm casing.
1.4 BS evaluation and analysis
Mushrooms with a suitable size for testing
(diameter: 4–5cm) were picked with closed caps and
bruised with three strokes of the bruise device
(Weijn et al. 2012). Pictures were taken 60min after
bruising and analyzed with a computer image
analysis system. The difference in whiteness index
between the bruised area and non‐bruised area of
ten mushrooms per tray was determined to get a
measurement of bruising sensitivity (BS). A higher BS
value represents a higher level of sensitivity to
bruising. The BS measurements were performed in
the same way for mushrooms of flush 1 and flush 2.
Statistical analysis was performed with Genstat
version 15 using data of flush 1 and flush 2,
separately. Since the factor RH was confounded with
compartment it was used in the analyses of variance
(ANOVA) as a block factor.
2 RESULTS
Performance of strains. According to ANOVA
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the factors Strain and casing depth (CD) had highly
significant influence on bruising sensitivity (Table 2).
The wetness of casing (CW) on the other hand was
an insignificant factor in flush 1 as well as in flush 2.
The three two‐factor interactions were significant
for BS of flush 1, but only Strain×CW were significant
for BS of flush 2. The three‐factor interaction was
not significant for BS of flush 1 and flush 2.
Table 2 Analyses of variance for bruising sensitivity of mushrooms from flushes 1 and 2
Source of variation Flush 1 Flush 2
Df Mean square F probability Df Mean square F probability
Cmpt stratum (RH) 1 133.77 1 26.85
Strain 3 753.25 <.001 3 386.33 <.001
CD 1 462.26 <.001 1 43.20 0.049
CW 1 18.31 0.168 1 5.60 0.475
Strain×CD 3 54.60 0.001 3 17.41 0.195
Strain×CW 3 29.95 0.028 3 36.72 0.021
CD×CW 1 44.71 0.032 1 13.56 0.267
Strain×CD×CW 3 3.62 0.767 3 13.16 0.311
Residual 111 9.53 110 10.91
Total 127 126
Note: RH indicates the relative humidity in the growing room; CD, the depth of casing; and CW, the wetness of casing.
The strains TO7 and CH1 were significantly less
sensitive to bruising than the other two strains TW4
and TW7 in both flush 1 and flush 2 (Table 3). This is
in agreement with the expectation. The resistant
strains TO7 and CH1 did not differ significantly in
bruising sensitivity, while TW4 showed to be a little
more sensitive to bruising than TW7. In general
there was not much difference in bruising sensitivity
of mushrooms from the first and second flush of the
bruising‐insensitive strains. For the sensitive strains
bruising sensitivity was more pronounced in the first
flush than in the second flush.
Impact of environmental conditions. The
thickness of casing layer (casing depth) had a highly
significant influence on BS ratings in flush 1 (Table 2).
Flush 1 mushrooms grown on 5cm casing soil were
significantly more sensitive to bruising than those
grown on a casing depth of 2.5cm. The flush 2
mushrooms showed an opposite response to casing
depth, although the differences in BS between the
two casing depths were small (Table 3). The
mushrooms grown on dry casing soil tend to be less
sensitive to bruising than those on normal soil, but
the differences were not significant.
Nevertheless, the interaction of wetness and
depth of casing (CW×CD) had significant effect on BS
of flush 1 mushrooms. The water content of the thin
casing layer (2.5cm) did not make a significant
difference in BS‐flush 1, but of the content in the 5cm
casing layer did make a difference, i.e. mushrooms
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Table 3 Means of bruising sensitivity for each level of the factor (strain and three environmental factors) set in flushes 1 and
2 of the bruising test
Factor Flush Factor level SEM*
Strain TO7 TW4 CH1 TW7
1 14.49 23.44 13.27 20.52 0.78
2 13.86 20.19 13.09 18.44 0.83
Casing depth (CD) 2.5cm 5cm
1 16.03 19.83 0.55
2 16.96 15.82 0.58
Relative humidity (block) (RH) 80% 87%
1 16.91 18.95 ‐
2 15.95 16.84 ‐
Wetness of casing (CW) Dry Normal
1 17.55 18.31 0.55
2 16.17 16.62 0.58
Note: *: SEM represents standard error of means.
produced on a dry layer of 5cm casing layer were
less sensitive to bruising than those from the 5cm
casing layer with a normal water content.
Mushrooms from the room with 87% RH were
generally more sensitive to bruising than those
produced at 80% RH. Influences of possible variation
in climate conditions other than RH between the
rooms cannot be ruled out. In general, mushrooms
from flush 2 were less sensitive to bruising than
those from flush 1 under most tested environmental
conditions (Table 3).
The interaction effects of strain by
environments. The interaction between strain and
CD was shown to have a significant influence on
bruising sensitivity of mushrooms from flush 1, but
not on those from flush 2 (Table 2). In flush 1,
mushrooms of three strains (TW4, CH1 and TW7)
produced on a layer of 2.5cm casing soil, were less
sensitive to bruising than those from a 5cm layer
(Fig. 1). Caps of TO7 produced on a thin or normal
casing layer did not show a significant difference in BS.
TW7 in flush 1 showed a significantly higher
sensitivity to bruising when grown on normal casing
(5cm) as compared to dry casing (5cm). On both dry
and normal casing mushrooms from strain TW4
grown on 2.5cm casing were significantly less
sensitive than those grown on 5cm casing.
Mushrooms of strain TO7 grown on dry casing were
significantly less sensitive to bruising than those
grown on normal casing soil in flush 2, but the
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Fig. 1 Mean performance of strains for bruising sensitivity of mushrooms (from flushes 1 and 2) produced under four different
growing conditions. Error bars indicate standard error of means. CW indicates the wetness of casing; CD indicates casing
thickness.
difference was not significant in flush 1. The other
three strains did not show a significant difference in
BS of flush 2 when they were grown on casing of
different water content (Fig. 1). CH1 in flush 1 was
generally less sensitive on 2.5cm casing but less
sensitive on 5cm casing in flush 2.
Differences in bruising sensitivity depending
growing conditions. The datasets on bruising
sensitivity of flush 1 and flush 2 were analyzed again
to get statistics for each of the eight possible
combinations of environmental conditions enabling
comparison between conditions with respect to
their suitability to discriminate strains for bruising
sensitivity. Factor combination C4 generated the
largest difference in bruising sensitivity among the
bruising resistant and bruising sensitive strains in
both flushes, i.e., a wider range of BS value
(Min‐Max). According to the BS value of the four
strains, this larger variation was mainly generated by
the fact that C4 increased the bruising sensitivity of the
two sensitive strains by a larger extent than the other 7
condition combinations (Table 4). The high coefficient
of variance (CV%) in flush 2 (23%) under the condition
of C4 was due to the large differences between
replicates of the two sensitive strains (TW4 and TW7).
In contrast, factor combination C6 generated the
smallest difference in BS among the four tested strains.
3 DISCUSSION
In this study, the main effects of genotype and
environmental factors on bruising sensitivity of
button mushroom were analyzed in a factorial design.
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Table 4 Statistics for bruising sensitivity (BS) of the four strains under all the eight environmental conditions (factor
combinations) applied
Code Factor combination Flush TO7 CH1 TW4 TW7 SEM Min‐max Diff min‐max CV (%)
C1 Dry/5cm/RH 0.8 1 12.85 15.61 25.59 19.68 1.09 10.90‐28.46 17.56 11.80
2 10.09 13.78 18.58 14.4 1.02 7.51‐20.14 12.61 14.30
C2 Normal/5cm/RH 0.8 1 16.65 11.55 23.77 25.82 1.56 9.41‐28.32 18.91 16.00
2 15.60 11.09 18.26 17.94 1.99 9.65‐23.72 14.07 23.50
C3 Dry/5cm/RH 0.87 1 13.97 15.24 24.57 23.39 1.50 10.86‐27.59 16.73 15.60
2 13.32 10.57 21.20 20.19 1.61 9.24‐25.21 15.97 19.80
C4 Normal/5cm/RH 0.87 1 15.37 17.01 30.24 25.99 1.68 12.34‐36.28 23.94 15.20
2 14.61 10.32 22.65 20.5 1.96 5.80‐30.16 24.36 23.00
C5 Dry/5cm/RH 0.8 1 15.41 12.59 20.18 14.16 1.38 9.08‐21.09 12.01 17.70
2 8.44 15.91 21.84 21.13 0.75 7.81‐23.08 15.27 8.90
C6 Normal/5cm/RH 0.8 1 13.89 10.52 16.72 15.56 0.92 8.88‐19.08 10.2 13.00
2 16.19 15.69 18.49 17.63 1.11 13.69‐22.05 8.36 13.10
C7 Dry/5cm/RH 0.87 1 12.6 12.63 23.48 18.9 1.77 9.35‐26.4 17.05 20.90
2 16.19 14.3 19.96 18.87 1.89 11.75‐26.11 14.36 21.80
C8 Normal/5cm/RH 0.87 1 15.21 11.02 22.99 20.63 1.41 9.82‐25.46 15.64 16.10
2 16.28 13.07 20.54 16.88 1.57 10.52‐26.77 16.25 18.80
Note: SEM: The standard error of the mean; Min‐max: The minimum and the maximum value of bruising sensitivity among the
four strains; Diff min‐max: The difference between the minimum and the maximum value; CV (%): The high coefficient of
variance.
Three environmental factors, i.e., relative humidity in
the growing room (RH) (although confounded with the
difference of growing rooms), casing depth (CD) and
wetness of casing (CW) were tested on four genotypes.
It turned out to be that bruising sensitivity of the four
strains was significantly influenced by the tested
environmental factors, i.e., bruising sensitivity was
sensitive to environmental change. Thus, it is necessary
to find out a suitable environmental condition to
generate sufficient phenotypic variations for genetic
studies of this trait and to guide the production of
bruising resistant mushrooms.
Bruising sensitivity was significantly influenced
by environmental factors and differed highly
significantly among strains (genotypes). In ANOVA
strain as a factor generated larger variance for BS
than the environmental factors. This indicates that
genotype is still the main source of phenotypic
variation of bruising sensitivity, and difference in
bruising sensitivity is mainly controlled by genetic
factors. As expected, the two preselected resistant
strains showed less sensitivity to bruising than the
two preselected sensitive strains in all the
environmental conditions. Bruising resistant strain is
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an urgent need for modern button mushroom
industry, and it might be able to reduce
bruising‐induced discoloration to a certain level
during mechanical harvesting. A combination of 87%
RH, 5cm depth of the casing and normal moisture is
used currently by most of the mushroom growers to
grow present‐day white commercial hybrids,
apparently because most agronomic traits are
optimal under these conditions. Since all commercial
mushroom strains are genetically similar
(Sonnenberg et al. 2011), this is routinely used as an
optimal condition by almost all mushroom growers.
However, it is not always an optimal condition for
strains with a low bruising sensitivity, as shown for
the commercial variety CH1. Despite the thick casing
layer (5cm) improved several agronomic traits, e.g.,
firmness, casing colonization, maturation, stipe
shape and size of mushroom compared to 2.5cm
casing layer (data not shown), mushrooms on 5cm
casing were more sensitive to bruising than those on
2.5cm casing. Although RH 87% (confounded with
the growing room) was beneficial for mushroom
distribution, firmness and maturation (data not
shown), it turned out to be a factor level generating
higher bruising sensitivity in flush 1 compared to
that of RH 80%. Dry casing is currently sold as a
different type of casing at some compost companies,
but moisture content of casing in this study as an
independent environmental factor did not show
significant influence on bruising sensitivity. This
might be due to the small difference in water
content between the two types of casing, which is
perhaps insufficient to generate phenotypic
variation. Thus, in order to obtain less bruised and
discolored button mushrooms during harvesting,
mushrooms should be grown on thinner casing and
in a less humid growing room.
Different strains favored different
environmental conditions for lower bruising
sensitivity, e.g., in flush 1, TO7 favored dry casing no
matter the depth of casing, and TW4 favored 2.5cm
casing no matter the levels of water content. Thus,
the environmental conditions used for commercial
mushroom production might not be applicable to all
new released cultivars, especially strains that are
genetically more distant from the present‐day
hybrids. The significant interaction effects of
genotype (strain) by environmental factors (G×E) on
bruising sensitivity (BS) also indicated that different
strains had different responses to environmental
changes. For instance, the two levels of relative
humidity in the growing room only gave significant
differences in BS for TO7 in flush 1 but not the other
three strains. In contrast, the two levels of casing
depth generated significant difference in BS for all
the other three strains but not TO7 in flush 1. The
significant G×E effects suggest that a particular
variety might need a special package of
environmental conditions to meet the superior
quality requirements.
The direction of the effects of environmental
factors on bruising sensitivity obtained in this study
is in several aspects different from that reported in
previous studies. Noble et al. (1997) observed that
mushrooms grown on 25mm casing (shallow)
showed a greater sensitivity to bruising than
mushrooms grown on 40 or 55mm casing which had
similar b values (P<0.001); Burton (2004) suggested
that to reduce bruising, mushrooms should be
grown wet (casing water and humidity) and allowed
to dry out somewhat towards the end of the crop
period (Burton 2004). However, mushrooms grown
GAO Wei et al. / Effects of environmental factors on bruising sensitivity of button mushrooms (Agaricus bisporus)
菌物学报
1385
on 5cm casing were significantly more sensitive to
bruising than those grown on 2.5cm casing in our
study, and no significant effect of water content of
casing on bruising sensitivity was observed. Burton
(2004) reported that first flush mushrooms grown in
high humidity (92%) were less sensitive to bruising
less than those grown in low humidity (85%). In
contrast, we found that first flush mushrooms grown
in high humidity (87%) were significantly more
bruised than those grown in low humidity (80%),
although the setup of our experiment does not allow
far reaching conclusions since variations in RH were
tested only once in two different rooms (one room
with high and one with low RH). There are a number
of possibilities to cause the discrepancies between
the previous and our studies. Because of the most
significant effects of genotype and significant
interaction effects of G×E, the primary reason for the
deviation of results in different studies is likely due
to different strains used in these studies. Four
distinct strains were tested in our study, of which
CH1 behaved quite differently with the other three
strains. This indicates that one genotype is
insufficient to give a general conclusion about the
effect of environmental factors on bruising
sensitivity. A commercial strain Hauser A12 was used
in the study of Nobel et al. (1997), but Burton (2004)
did not mention which strain he used to test the
bruising sensitivity (Noble et al. 1997; Burton 2004).
A second possibility might lie in the differences in
casing and watering schedule. In the study of Burton
(2004), the water potential of casing was monitored
weekly for the water content and water release
curves and adjusted by watering as required, and the
casing was kept moist by regular light watering
between each flush in the study of Noble et al.
(1997). The watering were scheduled in our study as
to keep the difference in levels of casing factors until
picking flush 1 (Supplementary file 1). Trays in flush
2 were watered at the same time, and thinner casing
was watered less than the 5cm casing. Thus, the
difference of factor level might be minimized during
flush 2. Additionally, different bruise method and
the way of measurement might also attribute the
opposite results. The bruising applied to mushrooms
in the study of Burton (2004) was considered to give
too much damage to mushrooms by Weijn et al.
(2012). In our study the background color (the
non‐bruised area) was included in the calculation,
but it was not included in the measurement of
bruising sensitivity in previous studies. Besides, the
difference in whiteness index between the bruised
area and non‐bruised area was used in this study for
the measurement of bruising sensitivity, and L or b
value was mainly used in previous studies of Burton
(2004) and Noble et al. (1997). This significant
difference in b value resulted from shallow and deep
casing was not observed by using loge(100‐L) value
(Noble et al. 1997). In addition, the compost and
casing materials in our study were bought from
commercial suppliers, but these materials were
self‐prepared in the two previous studies. In
conclusion, the results of our study were not
comparable with those reported in previous studies.
The discrepancies may be attributed to the
differences in strains, materials and methods used in
previous studies and this study.
The combination of 87% RH, normal moisture
content, and a 5cm casing generated the greatest BS
variation among the bruising sensitive and resistant
strains in both flush 1 and flush 2 (Table 4) mainly
due to an increase of BS of the two sensitive strains.
Later on, this selected commercial condition will be
used to cultivate the segregating populations for a
ISSN1672‐6472 CN11‐5180/Q Mycosystema November 22, 2016 Vol. 35 No. 11
http://journals‐myco.im.ac.cn
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large phenotypic variation to map the genetic
determinants of mushroom bruising sensitivity.
Since this is the environmental condition that
widely used in modern commercial mushroom farms
where hybrid strains are grown, and genotype is the
main factor determining bruising sensitivity,
breeding for new resistant cultivars might be the
only way to improve the bruising resistance of
current fresh mushrooms. Mushroom industries
worldwide are in need for new varieties adapted to
new cultivation techniques. At present, mechanical
harvesting is an effective technique to reduce the
labor costs. This work presented the effects of three
main environmental factors on bruising sensitivity of
button mushrooms and the factor combination that
generates the largest phenotypic variation among
strains. It will provide basic knowledge of genotype
by environmental interaction for genetic and
breeding study of the trait, bruising sensitivity.
Acknowledgements: We thank Amrah Weijn for her support
on picture scoring and Ed Hendrix for his work of mushroom
cultivation and picking.
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（本文责编：韩丽）