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Citation: Shi, H.; Zhong, J.; Liang, Y.;
Zhang, P.; Guo, L.; Wang, C.; Tang, Y.;
Lu, Y.; Sun, M. Aphid Resistance
Evaluation and Constitutive
Resistance Analysis of Eighteen
Lilies. Insects 2023,14, 936.
https://doi.org/10.3390/
insects14120936
Academic Editor: Mikhail V. Kozlov
Received: 28 October 2023
Revised: 23 November 2023
Accepted: 4 December 2023
Published: 8 December 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
insects
Article
Aphid Resistance Evaluation and Constitutive Resistance
Analysis of Eighteen Lilies
Huajin Shi, Jian Zhong , Yilin Liang, Peng Zhang , Liuyu Guo, Chen Wang, Yuchao Tang , Yufan Lu
and Ming Sun *
State Key Laboratory of Efficient Production of Forest Resources, Beijing Key Laboratory of Ornamental Plants
Germplasm Innovation and Molecular Breeding, National Engineering Research Center for Floriculture, Beijing
Laboratory of Urban and Rural Ecological Environment, Key Laboratory of Genetics and Breeding in Forest Trees
and Ornamental Plants of Ministry of Education, School of Landscape Architecture, Beijing Forestry University,
Beijing 100083, China; shihuajinbjfu@163.com (H.S.); zhongjianbjfu@163.com (J.Z.); elaineleung@bjfu.edu.cn (Y.L.);
gzyyndemailbox@163.com (P.Z.); guo1727805874@163.com (L.G.); wangchenbjfu@163.com (C.W.);
tangyuchao@bjfu.edu.cn (Y.T.); lyf1997@bjfu.edu.cn (Y.L.)
*Correspondence: sunmingbjfu@163.com
Simple Summary:
Aphis gossypii is an important pest that harms lilies and limits the development
of the lily industry. Improving host plant resistance is an effective and environmentally friendly
method for aphid control. We studied the resistance of 16 lily cultivars and 2 wild lily species
to A. gossypii and the biological characteristics of their leaves. Among the 18 tested lily plants,
‘Palazzo’, ‘Nymph’, ‘Cameleon’, and Lilium lancifolium showed strong resistance. The analysis of the
correlation between the thickness of leaf palisade tissue and the number of greenhouse aphids reveals
a significant negative correlation. This indicates that the thicker palisade tissue may be responsible
for the observed resistance. Identifying these lilies is important for managing aphid populations and
provides additional solutions for lily-integrated pest management.
Abstract:
Lilies (Lilium spp.) are famous bulb flowers worldwide, with high ornamental value. Aphid
damage has seriously constrained the development of the lily industry. In this study, the aphid
resistance of 16 lily cultivars and 2 wild lily species was characterized in the field and greenhouse.
Leaf color parameters, stomatal density and size, thickness of leaf layers, leaf waxy content, and
leaf water content were determined to explore the constitutive resistance of lilies. The results show
that there was a significant positive correlation between the number of aphids in the field and in the
greenhouse (p
≤
0.05, r = 0.47). This indicated that the level of aphid infestation in both the field
and the greenhouse is generally consistent across different types of lily plants. Among these 18 lilies,
‘Palazzo’, ‘Nymph’, ‘Cameleon’ and L. lancifolium were resistant to A. gossypii, while ‘Black Beauty’
and ‘Magnefique’ had poor resistance. The correlation analysis results showed that the number
of aphids was negatively correlated with leaf abaxial surface a*, stomatal size, water content, and
thickness of leaf palisade tissue and positively correlated with leaf distal axial surface b*, C*, and
waxy content. Among them, the correlation between the number of aphids and the thickness of leaf
palisade tissue reached a significant level (p
≤
0.05, r =
−
0.521). This indicated that the thickness
of the palisade tissue of lily leaves might be an important factor influencing the proliferation of
aphids. This study not only screened out aphid-resistant lilies but also established a crucial research
foundation for the targeted breeding and molecular breeding of lilies with aphid resistance.
Keywords: lily; Aphis gossypii; aphid resistance; palisade tissue
1. Introduction
Insect infestation has always been an important limiting factor for green crop pro-
duction. With the large-scale development of crop production, the threat of pests has
rapidly developed from a few species causing a small amount harm within a small area
Insects 2023,14, 936. https://doi.org/10.3390/insects14120936 https://www.mdpi.com/journal/insects
Insects 2023,14, 936 2 of 15
to large-scale damage being inflicted by multiple species with a high degree of harm [
1
].
Among them, aphids have become a severe pest, affecting the development of production
and the improvement of efficiency. Aphids often cluster on the young leaves and buds of
plants, causing serious damage through nutrient feeding, honeydew deposition, and viral
disease transmission [
2
]. This infestation leads to plants shriveling, affecting flowering and
fruiting, and reducing ornamental and application value, resulting in serious economic
losses [
3
]. The main method of aphid management is the use of pesticides, which not only
increases production costs but also causes harm to the environment [
4
–
7
]. Therefore, people
are beginning to search for alternative biological control methods for pesticides. Enhancing
host plant defenses through breeding is the most sustainable, effective, and eco-friendly
method [8].
Plants have their own defense systems that are developed during long-term inter-
actions with insects. These defense mechanisms can be classified into two categories:
constitutive resistance and induced resistance [
4
,
9
,
10
]. Constitutive resistance is inherent
in plants and is related to their genotypes [
11
,
12
]. It acts throughout their lifespan and
consists of physical barriers and chemical barriers [4,10,13]. Research on physical barriers
in plants currently focuses on factors such as leaf color, leaf trichomes, the wax content of
the leaf surface, leaf structure, and so on [
14
,
15
]. For example, many phytophagous insects
show a preference for a yellow-green color and have no tendency for a red color [
16
–
18
].
Resistant cultivars usually have longer and denser trichomes, as well as increased leaf
cuticle thickness, palisade tissue thickness, and spongy tissue thickness [15,19,20].
Lilies (Lilium spp.) are important perennial herbaceous bulbous plants that are pri-
marily distributed in the temperate regions of the Northern Hemisphere, including Eastern
Asia, Europe, and North America [
21
]. Lilies are cultivated as ornamental plants worldwide,
serving various purposes such as cut flowers, potted flowers, and urban landscaping [22].
Due to their beautiful flowers and pleasant fragrance, lilies occupy a significant portion of
the market in the global cut flower industry and are highly appreciated by customers [
23
].
Additionally, the steroidal saponins, flavonoids, and polysaccharides contained in the
Lilium are the main active substances with pharmacological activities, such as anti-tumor,
anti-inflammatory, and antioxidant activities [
21
]. Thus, lilies are also widely cultivated as
edible and medicinal plants in several Asian countries [22,24]
Biotic stress caused by pests and pathogens seriously hinders the sustainable develop-
ment of the lily industry. Among the pests that harm lilies, cotton aphids are particularly
problematic. They tend to gather on the tender leaves and buds of lilies to suck their
juices, which poses a significant threat to the plant’s health and ornamental value. In
addition, cotton aphids can cause sooty blotch and spread viruses such as lily mosaic virus
(LMV) and lily ring spot virus (LRSV) [
3
,
25
,
26
]. Despite the threat posed by cotton aphids,
there are very few studies related to aphid resistance in lilies. Currently, only a few lily
cultivars have been studied for their resistance to aphids, and little is known about the
mechanisms related to aphid resistance in lilies [
3
]. In this study, the aphid resistance of
eighteen lilies was evaluated, then the aphid-resistant mechanisms were systematically
explored by means of morphology, physiology, and metabolite analysis. This study aimed
to screen out aphid-resistant lily germplasms directly and lays an important research foun-
dation for targeted breeding and molecular breeding. Ultimately, the cultivation of new
aphid-resistant lily cultivars is expected to reduce the use of pesticides, lower production
costs, and contribute to the green ecological sustainability of the lily industry.
2. Materials and Methods
2.1. Plant Preparation
The 18 lily plant materials for testing were planted in the National Engineering Re-
search Center for Floriculture (China, Beijing, Changping District, 116.446
◦
E, 40.151
◦
N)
(Table 1). Before planting, the lily bulbs were soaked in carbendazim solution at
500 mg/L for 40 min, then the rotting and diseased scales were peeled off, and the basal
roots were pruned to 1 cm. The greenhouse lilies were grown in pots with single bulbs
Insects 2023,14, 936 3 of 15
(diameter of pots: 17 cm, height: 15 cm). The cultivation substrate was a mixture of
peat/perlite/vermiculite at a ratio of 5:1:1 with carbendazim added for sterilization. When
planting, we kept the bud tip of the lily bulbs upward, and the substrate was 5~8 cm above
the top of the lily bulbs.
Table 1. Eighteen tested lilies.
ID Cultivars/Species Germline
1 ‘Black Beauty’ OT
2 ‘Conca D0or’ OT
3 ‘Palazzo’ OT
4 ‘Nymph’ OT
5 ‘Friso’ OT
6 ‘Eyeliner’ LA
7 ‘Armandale’ LA
8 ‘Heartstrings’ LA
9 ‘Apricot Fudge’ LA
10 ‘Trendy Havana’ AA
11 ‘Secret Kiss’ AA
12 ‘Cameleon’ OO
13 ‘The Edge’ OO
14 ‘White Triumph’ LO
15 ‘Magnefique’ LO
16 ‘Watch Up’ LL
17 Lilium leucanthum S
18 Lilium lancifolium S
OT—Oriental hybrids
×
Trumpet hybrids; LA—Lilium longiflorum hybrids
×
Asiatic hybrids; AA—Asiatic hybrids;
O—Oriental hybrids; LO—L. longiflorum hybrids
×
Oriental hybrids; LL—L. longiflorum hybrids; S—lily species.
Field planting was carried out in early April. The treated lily bulbs were planted in the
experimental field according to the completely randomized zone group method, with the
burial depth consistent with that of potted plants. Finally, we watered the bulbs thoroughly
to ensure that they were tightly bonded to the soil.
2.2. Aphid Rear
The aphids, identified as A. gossypii, were harvested from lilies at the National Engi-
neering Research Center, in Beijing, China (Figure S2). The morphological identification
was based on the Journal of Economic Insects of China and the Ecological Atlas of Aphids
in Beijing [
27
,
28
]. A. gossypii used in the aphid resistance experiment were reared on the
lily cultivar ‘Magnefique’ at 22 ±2◦C and 65 ±5% relative humidity with a photoperiod
of 16:8 (light: dark) in the breeding greenhouse.
2.3. Aphid Resistance Test
2.3.1. Greenhouse Test
Five fourth-instar A. gossypi apterous nymphs were placed on the young leaves at the
top of each lily stem and confined with a voile bag (20
×
30 cm, mesh = 80) when the lilies
grew to a height of 10~15 cm [
29
] (Figure S1). The number of A. gossypii was counted after
10 days. The environmental conditions were kept the same as in Section 2.2. Five biological
replicates were set. No insecticides were used during the experiment.
2.3.2. Field Test
When the lilies in the field grew to a height of 10–15 cm, they were manually inoculated
with aphids for resistance evaluation tests. Each plant was inoculated with five fourth-
instar A. gossypi apterous nymphs, and the number of A. gossypi was counted after 10 days,
with 5 biological replicates for each plant material. It was ensured that no insecticides were
applied around the test field during the test period.
Insects 2023,14, 936 4 of 15
2.4. Determination of Biological Parameters of Lily Leaf
2.4.1. Leaf Preparation
The fifth and sixth leaves under the lily buds were collected to test when the lilies in
the greenhouse grew to a height of 10–15 cm.
2.4.2. Leaf Color
To determine L* (the lightness), a* (red to green axis), and b* (yellow to blue axis)
of the leaf’s adaxial and abaxial surfaces, we used a spectrophotometer (NF555, Nippon
Denshoku, Japan) to measure the middle part. We followed a previous study’s measuring
method [
18
]. Five biological replicates were set. Leaf color was analyzed using two color
spaces, CIELAB (L*a*b*) and CIE L*C*h*, selected based on their wide acceptance by the
industry and scientific community. C* (Chroma) and h* (Hue angle) were calculated using
the following formula:
C* = (a*2+ b*2)1/2
h* = arctan(b*/a*)
2.4.3. Leaf Stomata
Leaf stomata were investigated by using the imprinting method referenced from a
previous study [
30
]. Colorless nail polish was applied to the middle of the lower epidermis
of the lily fresh leaves, and gently torn off after the nail polish dried to make a clinical slide.
These slides were then observed and photographed with an optical microscope (Sdptop
CX40P, Sungrant, Suzhou, China). For each cultivar or species, three samples were selected,
and for each sample, five random visual fields were observed. The number of stomata,
stomatal length, and stomatal width of each field were counted with Image-Pro plus 6.0
(Media cybernetics, Rockville, MD, USA). Stomatal density, which is the number of stomata
per unit leaf area (square millimeters), was calculated.
2.4.4. Leaf Anatomical Structure
The lily fresh leaves were cut crosswise into 0.5 cm-wide slices at the center and fixed
with FAA fixative (Solarbio G2350) for 70 h. The fixed material was dehydrated in ethanol,
made transparent in xylene, embedded in paraffin, and then sliced using a microtome
(Leica RM 2016, Wetzlar, Germany) with a section thickness of 12
µ
m. Safranine O-fast
green staining was performed after the specimen was dried. Then, it was sealed with
neutral resin and photographed with an optical microscope (Sdptop CX40P, Sungrant,
Suzhou, China). Three samples were selected for each plant material, and each sample
was randomly observed in three fields of view. Data were measured by Image-Pro plus 6.0
(Media cybernetics, Rockville, MD, USA). The measured parameters included the thickness
of the leaf, upper epidermis, palisade tissue, spongy tissue, and lower epidermis. The
method of making paraffin sections and the measurement standard of data can be found in
a previous study [31].
2.4.5. Leaf Waxy Content
Leaf waxy content measurement was referenced and improved from a previous
study [
32
]. Fresh lily leaves weighing 2 g were cut and placed into a beaker, where
they were soaked in 30 mL of chloroform for a minute. Next, the liquid was filtered and
transferred into a clean beaker that had been weighed beforehand. The beaker was then
weighed again until all the chloroform had evaporated. Three replicates of the experi-
ment were carried out. The waxy content of the leaves was calculated using the following
formulas:
Leaf waxy content (mg/g) = (W2
−
W1)
×
1000/2.0 g (W1 is the mass of the clean
beaker, W2 is the mass of the beaker after chloroform evaporation).
Insects 2023,14, 936 5 of 15
2.4.6. Leaf Water Content
Once the lily leaves were clearly separated and tagged, they were quickly weighed
to avoid water loss. Then, the fresh leaves were placed in an oven at a temperature of
110
◦
C for 10 min and then kept at 80
◦
C until a constant dry weight was obtained [
33
]. The
determination was repeated three times for each plant material. The leaf water content was
calculated by using the following formulas:
Leaf water content (%) = (fresh weight −dry weight)/fresh weight ×100%
2.5. Statistical Analysis
All data were checked for normality and the homogeneity of variance before statistical
analysis. The normality of data distributions was tested using the Shapiro–Wilk normality
test. The homogeneity of variance between groups was tested using the Levene test for
homogeneity of variance. The aphid number, leaf color, leaf thickness, waxy content,
and other biological parameters of each lily were tested via one-way ANOVA followed
by Duncan’s multiple comparisons test with a 95% confidence interval of the difference.
Correlation analysis was performed by means of Pearson correlation coefficient calculation.
All statistical analyses were performed on SPSS20.0 (IBM SPSS, Somers, NY, USA). Images
were created using Origin software (2023b, MicroCal, East Northampton, MA, USA) and
Excel 2016 (Microsoft, Redmond, WA, USA).
3. Results and Discussion
3.1. Aphid Resistance
After 10 days of inoculation, aphids were found to have significantly increased on
‘Magnefique’ and ‘Black Beauty’ in the greenhouse, while ‘Cameleon’ had the lowest
aphid proliferation (Figure 1). These results indicate that ‘Magnefique’ and ‘Black Beauty’
displayed weaker aphid resistance compared with the other 16 plant materials, while
cultivars like ‘Cameleon’ demonstrated stronger aphid resistance. The field resistance
evaluation results also support this finding. However, there are some inconsistencies
regarding the aphid resistance of some plants in the greenhouse and field experiments. For
example, ‘Cameleon’ displayed the strongest aphid resistance in the greenhouse, while
‘Apricot Fudge’ had the lowest aphid proliferation in the field (Figure 1). Moreover,
greenhouse aphid populations were higher than field aphid populations for the same lily
materials. As shown in the figure, many aphids in the greenhouse gather on lilies’ tender
leaves and flower buds to absorb the juices (Figure 2). These results are probably because
greenhouse conditions are more favorable for aphid growth and reproduction and there is
less threat from their natural enemies present in the field [34–36].
Although greenhouse cut flower production is their main form of application, lilies are
still used in many applications as important flower beds and flower sea plants. Therefore,
this study combines the aphid resistance evaluation results of 18 lily plants obtained from
greenhouse and field evaluations, which provide higher practical application value for
the pest control and cultivation management of these lilies. Correlation analysis showed
a significant positive correlation between greenhouse aphid numbers and field aphid
numbers (p
≤
0.05, r = 0.47), indicating that the degree of aphid infestation in the field
and greenhouse is generally consistent among different lily plants (Figure 3). This laid the
foundation for the further exploration of the aphid resistance of lilies.
Insects 2023,14, 936 6 of 15
Insects 2023, 14, x FOR PEER REVIEW 6 of 16
Figure 1. Aphid numbers on eighteen lilies at 10 days after inoculation. Values are the mean ± SE (n
= 5).
Different lowercase leers above the columns indicate significant differences among different
lilies at the 0.05 level (Duncan’s test). Greenhouse aphid numbers, F = 6.126; df = 17, 72; p < 0.001.
Field aphid numbers, F = 2.055; df = 17, 72; p = 0.018.
Figure 2. Phenotypes of eighteen lily plants at ten days after inoculation in the greenhouse. The
boom left image shows the top part of the lily magnified three times. (A) ‘Black Beauty’; (B) ‘Conca
D′or’; (C) ‘Palazzo’; (D) ‘Nymph’; (E) ‘Friso’; (F) ‘Eyeliner’; (G) ‘Armandale’; (H) ‘Heartstrings’; (I)
‘A p r i c o t F udge’; (J) ‘Trendy Havana’; (K) ‘Secret Kiss’; (L) ‘Cameleon’; (M) ‘The Edge’; (N) ‘White
Triumph’; (O) ‘Magnefique’; (P) ‘Watch Up’; (Q) Lilium leucanthum; (R) Lilium lancifolium.
Although greenhouse cut flower production is their main form of application, lilies
are still used in many applications as important flower beds and flower sea plants. There-
fore, this study combines the aphid resistance evaluation results of 18 lily plants obtained
from greenhouse and field evaluations, which provide higher practical application value
for the pest control and cultivation management of these lilies. Correlation analysis
showed a significant positive correlation between greenhouse aphid numbers and field
aphid numbers (p ≤ 0.05, r = 0.47), indicating that the degree of aphid infestation in the
Figure 1.
Aphid numbers on eighteen lilies at 10 days after inoculation. Values are the mean
±
SE
(n= 5). Different lowercase letters above the columns indicate significant differences among different
lilies at the 0.05 level (Duncan’s test). Greenhouse aphid numbers, F = 6.126; df = 17, 72; p< 0.001.
Field aphid numbers, F = 2.055; df = 17, 72; p= 0.018.
Insects 2023, 14, x FOR PEER REVIEW 6 of 16
Figure 1. Aphid numbers on eighteen lilies at 10 days after inoculation. Values are the mean ± SE (n
= 5).
Different lowercase leers above the columns indicate significant differences among different
lilies at the 0.05 level (Duncan’s test). Greenhouse aphid numbers, F = 6.126; df = 17, 72; p < 0.001.
Field aphid numbers, F = 2.055; df = 17, 72; p = 0.018.
Figure 2. Phenotypes of eighteen lily plants at ten days after inoculation in the greenhouse. The
boom left image shows the top part of the lily magnified three times. (A) ‘Black Beauty’; (B) ‘Conca
D′or’; (C) ‘Palazzo’; (D) ‘Nymph’; (E) ‘Friso’; (F) ‘Eyeliner’; (G) ‘Armandale’; (H) ‘Heartstrings’; (I)
‘A p r i c o t F udge’; (J) ‘Trendy Havana’; (K) ‘Secret Kiss’; (L) ‘Cameleon’; (M) ‘The Edge’; (N) ‘White
Triumph’; (O) ‘Magnefique’; (P) ‘Watch Up’; (Q) Lilium leucanthum; (R) Lilium lancifolium.
Although greenhouse cut flower production is their main form of application, lilies
are still used in many applications as important flower beds and flower sea plants. There-
fore, this study combines the aphid resistance evaluation results of 18 lily plants obtained
from greenhouse and field evaluations, which provide higher practical application value
for the pest control and cultivation management of these lilies. Correlation analysis
showed a significant positive correlation between greenhouse aphid numbers and field
aphid numbers (p ≤ 0.05, r = 0.47), indicating that the degree of aphid infestation in the
Figure 2.
Phenotypes of eighteen lily plants at ten days after inoculation in the greenhouse. The
bottom left image shows the top part of the lily magnified three times. (
A
) ‘Black Beauty’; (
B
) ‘Conca
D
0
or’; (
C
) ‘Palazzo’; (
D
) ‘Nymph’; (
E
) ‘Friso’; (
F
) ‘Eyeliner’; (
G
) ‘Armandale’; (
H
) ‘Heartstrings’;
(
I
) ‘Apricot Fudge’; (
J
) ‘Trendy Havana’; (
K
) ‘Secret Kiss’; (
L
) ‘Cameleon’; (
M
) ‘The Edge’; (
N
) ‘White
Triumph’; (O) ‘Magnefique’; (P) ‘Watch Up’; (Q)Lilium leucanthum; (R)Lilium lancifolium.
Insects 2023,14, 936 7 of 15
Insects 2023, 14, x FOR PEER REVIEW 7 of 16
field and greenhouse is generally consistent among different lily plants (Figure 3). This
laid the foundation for the further exploration of the aphid resistance of lilies.
Figure 3. Scaerplot of correlation between greenhouse aphid population and field aphid popula-
tion (Pearson correlation coefficient).
Different plants have various insect resistance strategies such as the waxiness of the
epidermis, stomatal density, and deeper vascular bundle burial depth [10]. However, it is
not yet clear why there are significant differences in resistance among various lily plants.
After ten days of inoculation, there were notable differences in aphid populations among
different lilies. We hypothesize that certain biological properties of lily leaves play a cru-
cial role in hindering the aphids (Figure 1).
3.2. Leaf Color
After analysis, significant differences (p < 0.05) were found among different lilies in
L*, a*, b*, C*, and h* on the adaxial and the abaxial surfaces of leaves. It is well-docu-
mented that many phytophagous insects, such as aphids, prefer yellow-green light [37,38].
Consequently, green leaves are more likely to be infested by various insect species as com-
pared to red leaves [16,17]. In this study, ‘Secret Kiss’ had the smallest distal a* value,
indicating the most intense green color, and the largest distal b* value, indicating the yel-
lowest color, and it was the least aphid-resistant (Table 2; Figures 1 and S3). In addition,
the highly aphid sensitive ‘Magnefique’ also had a very low a* value and high b* value on
both the adaxial and abaxial surfaces. The aphid-resistant lilies such as ‘Palazzo’, ‘White
Triumph’, and ‘Conca D’or’ exhibited a lower value of brightness (L*), yellowness (b*),
and chromaticity (C*) and higher values of redness (a*) on both the adaxial and abaxial
surfaces. These results align with the theoretical understanding of aphid visual ecology,
which suggests that phytophagous insects may favor specific colors or intensities in their
preferred plants [39].
R² = 0.2208
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350 400 450
Field aphids number
Greenhouse aphids number
Figure 3.
Scatterplot of correlation between greenhouse aphid population and field aphid population
(Pearson correlation coefficient).
Different plants have various insect resistance strategies such as the waxiness of the
epidermis, stomatal density, and deeper vascular bundle burial depth [
10
]. However, it is
not yet clear why there are significant differences in resistance among various lily plants.
After ten days of inoculation, there were notable differences in aphid populations among
different lilies. We hypothesize that certain biological properties of lily leaves play a crucial
role in hindering the aphids (Figure 1).
3.2. Leaf Color
After analysis, significant differences (p< 0.05) were found among different lilies in L*,
a*, b*, C*, and h* on the adaxial and the abaxial surfaces of leaves. It is well-documented that
many phytophagous insects, such as aphids, prefer yellow-green light [
37
,
38
]. Consequently,
green leaves are more likely to be infested by various insect species as compared to red
leaves [
16
,
17
]. In this study, ‘Secret Kiss’ had the smallest distal a* value, indicating the most
intense green color, and the largest distal b* value, indicating the yellowest color, and it was
the least aphid-resistant (Table 2; Figures 1and S3). In addition, the highly aphid sensitive
‘Magnefique’ also had a very low a* value and high b* value on both the adaxial and abaxial
surfaces. The aphid-resistant lilies such as ‘Palazzo’, ‘White Triumph’, and ‘Conca D’or ’
exhibited a lower value of brightness (L*), yellowness (b*), and chromaticity (C*) and higher
values of redness (a*) on both the adaxial and abaxial surfaces. These results align with
the theoretical understanding of aphid visual ecology, which suggests that phytophagous
insects may favor specific colors or intensities in their preferred plants [39].
Insects 2023,14, 936 8 of 15
Table 2. Color parameters of the adaxial and abaxial leaves of eighteen lilies.
Cultivars/Species Colorimetric Characteristics of the Leaf Apaxial Plane Colorimetric Characteristics of the Leaf Paraxial Plane
L* a* b* C* h* L* a* b* C* h*
‘Black Beauty’ 37.04 ±0.81 gh −18.16 ±0.79 efg 23.32 ±1.29 cde 29.56 ±1.5 bc −0.908 ±0.008 cd 48.3 ±0.71 def −15.23 ±0.23 efg 23.91 ±0.42 abc 28.35 ±0.47 ab −1.006 ±0.004
efgh
‘Conca D0or’ 33.51 ±0.63 i −15.31 ±0.89 bcd 18.54 ±1.85 fg 24.06 ±2 de −0.874 ±0.019 b 47.23 ±0.88 ef −12.37 ±0.35 ab 18.67 ±0.71 gh 22.4 ±0.76 gh −0.984 ±0.011
abcde
‘Palazzo’ 35.56 ±1.13 hi −18.03 ±0.36 efg 24.44 ±0.89 bcd 30.37 ±0.92 bc −0.934 ±0.008 def 48.28 ±0.62 def −13.93 ±0.36 cd 20.44 ±0.77 efg 24.74 ±0.82 defg −0.972 ±0.009 ab
‘Nymph’ 35.66 ±1.3 hi −16.95 ±0.29 def 22.28 ±0.46 def 28 ±0.53 cd −0.92 ±0.004 de 46.46 ±1.02 f −13.97 ±0.23 cd 20.63 ±0.43 efg 24.91 ±0.47 def −0.976 ±0.006
abcd
‘Friso’ 33.19 ±0.76 i −15.76 ±0.42 bcd 19.1 ±0.95 fg 24.77 ±1 de −0.878 ±0.011 b 47.52 ±0.4 def −12.75 ±0.37 ab 18.8 ±0.84 fgh 22.72 ±0.9 fgh −0.972 ±0.008 ab
‘Eyeliner’ 40.75 ±0.23 def −16.67 ±0.47 cdef 21.93 ±0.76 def 27.55 ±0.89 −0.92 ±0.005 de 49.34 ±0.81 cde −15.13 ±0.55 efg 22.38 ±1.12 cde 27.02 ±1.21 bcd −0.974 ±0.011
abc
‘Armandale’ 45.22 ±1.14 ab −18.16 ±0.53 efg 23.54 ±1.24 cde 29.74 ±1.31 bc −0.912 ±0.011 cd 52.63 ±0.51 ab −14.77 ±0.25 def 22.86 ±0.32 bcd 27.22 ±0.39 bc −0.996 ±0.004
cdef
‘Heartstrings’ 46.41 ±0.49 a −14.85 ±0.54 bc 23.01 ±0.8 cde 27.39 ±0.96 cd −0.996 ±0.004 h 52.7 ±0.21 ab −14.61 ±0.24 de 20.9 ±0.5 def 25.5 ±0.54 cde −0.96 ±0.007 a
‘Apricot Fudge’ 40.7 ±1.08 def −16.27 ±0.67
bcde 21.85 ±1.05 def 27.24 ±1.24 cde −0.932 ±0.007 def 53.04 ±0.36 a −14.82 ±0.2 def 24.51 ±0.36 abc 28.64 ±0.4 ab −1.026 ±0.002 h
‘Trendy Havana’ 41.81 ±0.45 cde −19.41 ±0.55 g 27.32 ±1.56 ab 33.53 ±1.59 ab −0.948 ±0.014 ef 52.53 ±0.46 ab −15.18 ±0.16 efg 24.72 ±0.25 ab 29.01 ±0.3 ab −1.022 ±0.002 gh
‘Secret Kiss’ 42.82 ±0.32 bcd −19.48 ±0.93 g 29.39 ±2.09 a 35.27 ±2.25 a −0.982 ±0.013 gh 50.75 ±0.52 bc −16.09 ±0.31 g 25.78 ±0.62 a 30.39 ±0.69 a −1.014 ±0.002
fgh
‘Cameleon’ 37.64 ±1.11 gh −18.22 ±0.54 fg 24.47 ±1.28 bcd 30.52 ±1.35 bc −0.93 ±0.011 def 46.67 ±0.17 f −15.14 ±0.56 efg 23.7 ±0.66 abc 28.12 ±0.86 ab −1.006 ±0.005
efgh
‘The Edge’ 35.37 ±0.95 hi −14.67 ±0.76 b 17.96 ±0.96 g 23.19 ±1.23 e −0.884 ±0.002 bc 47.21 ±0.8 ef −12.2 ±0.44 a 17.81 ±0.42 h 21.59 ±0.58 h −0.97 ±0.009 ab
‘White Triumph’ 35.41 ±0.54 hi −12.4 ±0.68 a 13.34 ±0.78 h 18.21 ±1.03 f −0.822 ±0.008 a 48.49 ±0.84 def −13.38 ±0.35 bc 19.55 ±0.69 fgh 23.69 ±0.76 efgh −0.97 ±0.007 ab
‘Magnefique’ 43.79 ±0.38 bc −19.01 ±0.16 g 26.62 ±0.43 abc 32.72 ±0.44 ab −0.952 ±0.005 f 52.74 ±0.27 ab −15.78 ±0.25 fg 23.97 ±0.64 abc 28.7 ±0.66 ab −0.99 ±0.006
bcde
‘Watch Up’ 39.1 ±0.66 fg −15.24 ±0.27 bcd 18.49 ±0.62 fg 23.97 ±0.64 de −0.878 ±0.008 b 49.57 ±0.97 cd −13.34 ±0.4 bc 20.91 ±0.59 def 24.8 ±0.71 def −1±0.005 efg
Lilium leucanthum 39.34 ±0.88 efg −15.52 ±0.67 bcd 22.17 ±1.47 def 27.06 ±1.58 cde −0.956 ±0.011 fg 48.21 ±1.05 def −13.21 ±0.48 abc 20.53 ±1.2 efg 24.42 ±1.26 efg −0.998 ±0.012 def
Lilium lancifolium 38.42 ±0.66 fg −14.61 ±0.49 b 19.93 ±0.82 efg 24.71 ±0.94 de −0.936 ±0.007 def 51.61 ±0.45 ab −13.15 ±0.33 abc 18.82 ±0.72 fgh 22.96 ±0.76 fgh −0.96 ±0.009 a
F 23.526 10.971 10.909 10.671 19.107 12.386 11.095 13.044 12.799 8.031
df 17, 72 17, 72 17, 72 17, 72 17, 72 17, 72 17, 72 17, 72 17, 72 17, 72
pvalue <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
Values expressed as mean ±SE (n= 5); means in the same column followed by different lowercase letters are significantly different at the 0.05 level (Duncan’ test).
Insects 2023,14, 936 9 of 15
3.3. Leaf Stomata
Lilies’ stomatal length, stomatal width, and stomatal density of lilies were found
to be significantly different (p< 0.05). Previous studies have shown that larger stomatal
densities can alter leaf surface topography, leading to behavioral responses from insects [
15
].
Plant aphid-resistant varieties tend to have a smaller stomatal size and higher stomatal
density [
30
]. The stomatal length and stomatal width of L. leucanthum, which is weakly
resistant to aphids, were significantly smaller than those of other lilies, and the stomatal
density was significantly higher than that of other lilies. The more aphid-resistant ‘Conca
D’or’, ‘Palazzo’ had a larger stomatal length and stomatal width, as well as lower stomatal
density (Table 3; Figures 1and S4). This finding is contrary to previous studies, which
have suggested that plants with increased stomatal sizes and greater stomatal densities
enable the conversion of additional photoassimilates, resulting in strengthened cell walls
and enhanced tolerance to aphids [
40
]. The stomata play a complex role in influencing
plant aphid resistance.
Table 3. Stomatal parameters of eighteen lilies.
Cultivars/Species Stomatal Length
(µm) Stomatal Width (µm) Stomatal Density
(Number/mm2)
‘Black Beauty’ 83.86 ±2.72 g 56.45 ±1.35 def 45.73 ±2.07 cd
‘Conca D0or’ 114.24 ±2.22 b 70.73 ±1.51 a 24.55 ±0.33 gh
‘Palazzo’ 113.74 ±1.72 b 70.6 ±1.94 a 32.93 ±0.49 f
‘Nymph’ 92.64 ±1.53 ef 59.25 ±0.57 cd 47.45 ±1.64 cd
‘Friso’ 111.28 ±2.45 b 63.44 ±0.7 bc 28.92 ±1.27 fg
‘Eyeliner’ 107.73 ±4.5 bc 65.18 ±2.29 b 30.98 ±0.69 f
‘Armandale’ 96.58 ±2.44 de 59.91 ±1.76 cd 39.42 ±0.66 e
‘Heartstrings’ 101.25 ±3.77 cd 58.37 ±1.08 de 47.13 ±2.53 cd
‘Apricot Fudge’ 125.98 ±3.48 a 69.94 ±2.13 a 17.15 ±0.46 i
‘Trendy Havana’ 99.34 ±3.64 de 70.66 ±1.8 a 22.43 ±0.6 h
‘Secret Kiss’ 82.33 ±1.75 g 53.61 ±0.8 ef 45.43 ±1.76 cd
‘Cameleon’ 81.87 ±2.67 g 59.5 ±2.3 cd 70.3 ±2.47 b
‘The Edge’ 85.91 ±1.87 fg 55.95 ±1.92 def 44.87 ±1.14 d
‘White Triumph’ 114.96 ±1.98 b 58.1 ±0.96 de 39.15 ±0.96 e
‘Magnefique’ 74.57 ±1.09 h 56.02 ±0.72 def 50.73 ±1.07 c
‘Watch Up’ 72.38 ±1.54 h 48.31 ±0.94 gh 44.82 ±1.16 d
Lilium leucanthum 62.98 ±1.15 i 47.41 ±1.24 h 90.12 ±4.07 a
Lilium lancifolium 97.76 ±1.35 de 52.45 ±1.19 fg 49.13 ±2.18 cd
F 47.17 23.90 102.18
df 17, 252 17, 252 17, 252
pvalue <0.001 <0.001 <0.001
Values expressed as mean
±
SE (n= 15); means in the same column followed by different lowercase letters are
significantly different at the 0.05 level (Duncan’s test).
3.4. Leaf Anatomical Structure
Plants have evolved various constitutive defense systems to protect themselves from
insect damage. One such defense mechanism is the presence of palisade tissue and spongy
tissue, which act as physical barriers to resist insect attacks [
41
]. Researchers have pre-
viously compared the resistance of cucumbers to aphids and found that the deeper the
vascular bundles are buried, the stronger the cucumber’s resistance to aphids. This may be
due to the increased difficulty aphids face in feeding on the vascular sap [
31
]. In this study,
significant differences (p< 0.05) in the thickness were observed among all the lilies tested.
‘Cameleon’ exhibited the highest leaf thickness, measuring 570.41
µ
m, and demonstrated
greater resistance to aphids. The weakly aphid-resistant ‘Secret Kiss’ had the thinnest
palisade tissue at 32.87
µ
m (Table 4; Figures 1and S5). There are similar cases in previ-
ous studies, like a pear tree study which revealed that leaf thickness and palisade tissue
thickness are the key factors influencing aphid feeding [31].
Insects 2023,14, 936 10 of 15
Table 4. The thickness of each layer of eighteen lilies.
Cultivars/Species Leaf Thickness (µm) Leaf Epidermis
Thickness (µm)
Leaf Palisade Tissue
Thickness (µm)
Leaf Spongy Tissue
Thickness (µm)
Leaf Lower
Epidermis
Thickness (µm)
‘Black Beauty’ 369.29 ±9.04 ijk 48.85 ±2.08 bcde 44.56 ±0.84 cde 243.25 ±8.65 efgh 30.69 ±0.97 de
‘Conca D0or’ 465.57 ±21.8 bcdef 73.7 ±0.72 a 64.67 ±2.74 abc 284.56 ±19.11 defg 43.33 ±2.92 abc
‘Palazzo’ 426.97 ±21.84 defgh 44.71 ±0.89 cde 42.51 ±4.95 d 305.15 ±22.68 cd 32.67 ±1.73 de
‘Nymph’ 369.43 ±13.06 ijk 41.84 ±4.12 def 60.81 ±1.65 abcd 233.41 ±10.18 gh 36.23 ±3.17 bcde
‘Friso’ 449.7 ±20.18 cdefg 60.46 ±1.77 b 68.79 ±4.26 ab 289.59 ±18.36 def 37.69 ±1.88 bcd
‘Eyeliner’ 450.53 ±23.23 cdefg 48.56 ±7.3 bcde 59.66 ±3.44 abcd 303.53 ±15.98 cd 33.08 ±4.06 de
‘Armandale’ 420.45 ±25.76 efghi 46.89 ±2.82 cde 66.93 ±2.57 ab 275.98 ±23.24 defg 31.42 ±2.83 de
‘Heartstrings’ 470.6 ±23.65 bcde 78.12 ±6.78 a 56.42 ±6.12 bcd 293.41 ±27.6 de 49.74 ±1.74 a
‘Apricot Fudge’ 346.5 ±7.63 jk 40.49 ±4.86 ef 55.88 ±8.13 bcd 207.19 ±19.27 h 44.03 ±4.59 ab
‘Trendy Havana’ 406.85 ±6.72 ghi 75.32 ±3.85 a 58.64 ±3.73 bcd 240.2 ±16.14 fgh 44.4 ±3.81 ab
‘Secret Kiss’ 326.12 ±13.87 k 32.87 ±1.58 f 58.01 ±4.67 bcd 199.12 ±11.85 h 34.03 ±3.36 cde
‘Cameleon’ 570.41 ±8.39 a 55.92 ±2.83 bc 63.9 ±4.48 abc 414.58 ±3.76 a 34.15 ±2.19 cde
‘The Edge’ 380.16 ±11.72 hij 50.54 ±4.43 bcde 45.62 ±6.96 cde 238.26 ±17.55 fgh 39.13 ±4.28 bcd
‘White Triumph’ 519.18 ±30.57 b 53.82 ±3.61 bcd 54.37 ±11.78 bcd 373.21 ±13.52 ab 38.75 ±1.2 bcd
‘Magnefique’ 500.19 ±11.74 bc 46.61 ±0.12 cde 69.4 ±6.56 ab 345.27 ±15.33 bc 34.13 ±1.59 cde
‘Watch Up’ 411.08 ±9.59 fghi 43.06 ±1.29 def 44.77 ±3.32 cde 280.61 ±8.6 defg 35.07 ±1.64 bcde
Lilium leucanthum 478.87 ±9.07 bcd 45.33 ±3.5 cde 79.73 ±13.13 a 321.71 ±10.18 cd 29.88 ±3.09 de
Lilium lancifolium 266.18 ±5.89 l 49.68 ±3.16 bcde 50.2 ±4.33 bcd 142.59 ±9.62 i 27.66 ±2.13 e
F 19.176 11.765 2.741 16.04 4.268
df 17, 36 17, 36 17, 36 17, 36 17, 36
pvalue <0.001 <0.001 0.005 <0.001 <0.001
Values expressed as mean
±
SE (n= 3); means in the same column followed by different lowercase letters are
significantly different at the 0.05 level (Duncan’s test).
3.5. Leaf Waxy Content
Leaf surface wax is a layer of lipophilic compounds that covers the plant surface [
42
].
It serves to prevent water loss and resist insect attacks. Leaves with a thicker waxy structure
have smoother surfaces, which reduces the attachment ability of phytophagous insects
and thus leads to lower egg drop and hatchability, resulting in reduced pest damage. A
previous study found that removing the wax from the surface of the leaves promoted
cochineal insect feeding on Brassicaceae [
43
]. Additionally, the wax content of cabbage was
significantly and negatively correlated with green peach aphid preference [36].
However, in this study, the most severely aphid-infested lilies, ‘Magnefique’ and ‘Black
Beauty’, had the highest wax content at 1.45 mg/g and 1.44 mg/g, respectively. On the other
hand, aphid-resistant lilies, such as ‘Conca D
0
or’ and ‘Palazzo’, had the lowest wax content
of 0.71 mg/g and 0.79 mg/g, respectively (Figures 1and 4). This anomaly is not exceptional.
Another previous study found that epidermal waxes can also benefit plants by influencing
natural enemy insects [
44
]. Lower wax content increases the attachment ability of natural
enemy insects such as Hippodamia convergens Linnaeus (Ladybirds, Coleoptera), thereby
promoting their predation on phytophagous insects [
45
,
46
]. These findings highlight the
complexity of the role of surface waxes in the tertiary trophic relationship between plants,
phytophagous insects, and natural enemy insects.
3.6. Leaf Water Content
The water content of lily leaves ranged from 86.02% to 91.67%, with significant differences
(p< 0.05). Previous studies have shown a positive correlation between host feeding preference
and leaf water content [
41
]. While L. leucanthum is susceptible to aphids, its water content was
significantly lower than that of the other lilies, at 86.02% (Figures 1and 5). The highest water
content was found in ‘Eyeliner’, ‘Armandale’, at 91.67% and 91.62%, respectively, but they
are not aphid-resistant. Previous studies have shown that a decrease in leaf water content
and leaf water potential increases the difficulty of aphids to feed in the xylem and shortens
the feeding time [
47
]. The decrease in water potential elevated the total amino acid content
of the plant, including asparagine and valine, which are critical for aphid performance.
However, aphids did not benefit from improved phloem sap quality [
48
]. At a lower water
content, the expression of JA- and SA-related genes rose in plants due to drought stress,
Insects 2023,14, 936 11 of 15
which in turn acted as a suppressor of aphids [
49
]. The water content of leaves has a more
complex relationship with aphid populations.
Insects 2023, 14, x FOR PEER REVIEW 12 of 16
findings highlight the complexity of the role of surface waxes in the tertiary trophic rela-
tionship between plants, phytophagous insects, and natural enemy insects.
Figure 4. Leaf wax content of eighteen lilies. Values are the mean ± SE (n = 3). Different lowercase
leers above the columns indicate significant differences among different lilies, Duncan’s test, alpha
= 0.05 (F = 2.606; df = 17, 36; p = 0.008).
3.6. Leaf Water Content
The water content of lily leaves ranged from 86.02% to 91.67%, with significant dif-
ferences (p < 0.05). Previous studies have shown a positive correlation between host feed-
ing preference and leaf water content [41]. While L. leucanthum is susceptible to aphids, its
water content was significantly lower than that of the other lilies, at 86.02% (Figures 1 and
5). The highest water content was found in ‘Eyeliner’, ‘Armandale’, at 91.67% and 91.62%,
respectively, but they are not aphid-resistant. Previous studies have shown that a decrease
in leaf water content and leaf water potential increases the difficulty of aphids to feed in
the xylem and shortens the feeding time [47]. The decrease in water potential elevated the
total amino acid content of the plant, including asparagine and valine, which are critical
for aphid performance. However, aphids did not benefit from improved phloem sap qual-
ity [48]. At a lower water content, the expression of JA- and SA-related genes rose in plants
due to drought stress, which in turn acted as a suppressor of aphids [49]. The water con-
tent of leaves has a more complex relationship with aphid populations.
Figure 4.
Leaf wax content of eighteen lilies. Values are the mean
±
SE (n= 3). Different lower-
case letters above the columns indicate significant differences among different lilies, Duncan’s test,
alpha = 0.05 (F = 2.606; df = 17, 36; p= 0.008).
Insects 2023, 14, x FOR PEER REVIEW 13 of 16
Figure 5. Leaf water content of eighteen lilies. Values are the mean ± SE (n = 3). Different lowercase
leers above the columns indicate significant differences among different lilies, Duncan’s test, alpha
= 0.05 (F = 16.276; df = 17, 36; p < 0.001).
3.7. Correlation between the Aphid Population and Biological Parameters of Lily Leaves
In this study, Pearson’s correlation coefficient was utilized to investigate the relation-
ship between various biological parameters of lilies and their ability to resist aphids. The
results indicate that the number of aphids in the greenhouse was significantly negatively
correlated with the thickness of the leaf palisade tissue (p ≤ 0.05, r = −0.521), suggesting
that thicker leaf tissue made it harder for aphids to feed and resulted in a lower aphid
population (Figure 6). This finding is consistent with a previous study which showed that
the thickness of palisade tissue was one of the main factors influencing pear’s resistance
to pear psylla [31]. Additionally, the findings indicate that parameters such as stomatal
length, stomatal width, water content, and leaf abaxial surface a* were negatively corre-
lated with the aphid population, while wax content, leaf abaxial surface b*, and C* were
positively correlated. Although these correlations did not reach statistical significance,
they still suggest that these leaf traits have some influence on aphid resistance in lilies.
Previous studies have also reported similar findings [10,37], indicating that a combination
of factors may determine the resistance of lilies to aphids.
Figure 5.
Leaf water content of eighteen lilies. Values are the mean
±
SE (n= 3). Different lower-
case letters above the columns indicate significant differences among different lilies, Duncan’s test,
alpha = 0.05 (F = 16.276; df = 17, 36; p< 0.001).
Insects 2023,14, 936 12 of 15
3.7. Correlation between the Aphid Population and Biological Parameters of Lily Leaves
In this study, Pearson’s correlation coefficient was utilized to investigate the relation-
ship between various biological parameters of lilies and their ability to resist aphids. The
results indicate that the number of aphids in the greenhouse was significantly negatively
correlated with the thickness of the leaf palisade tissue (p
≤
0.05, r =
−
0.521), suggesting
that thicker leaf tissue made it harder for aphids to feed and resulted in a lower aphid
population (Figure 6). This finding is consistent with a previous study which showed that
the thickness of palisade tissue was one of the main factors influencing pear’s resistance to
pear psylla [
31
]. Additionally, the findings indicate that parameters such as stomatal length,
stomatal width, water content, and leaf abaxial surface a* were negatively correlated with
the aphid population, while wax content, leaf abaxial surface b*, and C* were positively
correlated. Although these correlations did not reach statistical significance, they still
suggest that these leaf traits have some influence on aphid resistance in lilies. Previous
studies have also reported similar findings [
10
,
37
], indicating that a combination of factors
may determine the resistance of lilies to aphids.
Insects 2023, 14, x FOR PEER REVIEW 14 of 16
Figure 6. Correlation between the number of greenhouse aphids and biological parameters of lily
leaves (Pearson correlation coefficient). Color code ranges from blue = strong negative correlation (r
= −1) to white = no correlation (r = 0) to red = positive correlation (r = +1). Labels with “*” indicate
the significant correlations at different levels (* p ≤ 0.05; ** p ≤ 0.01).
4. Conclusions
As a limitation to the development of the lily industry, A. gossypii has aracted much
aention from researchers. This study evaluated the aphid resistance of eighteen lilies in
the field and greenhouse. The correlation between the number of aphids and lily leaf color
parameters, stomatal density and size, thickness of leaf layers, leaf surface wax content,
and leaf water content was assessed. The results show that ‘Palazzo’, ‘Nymph’ and L. lanci-
folium displayed higher resistance to A. gossypii. In contrast, ‘Black Beauty’ and ‘Mag-
nefique’ were more susceptible to A. gossypii than the other lilies. There was a significant
negative correlation between greenhouse aphid number and leaf palisade tissue thickness.
The resistant lilies ‘Palazzo’, ‘Nymph’, ‘Cameleon’, and L. lancifolium have great potential
to be used for breeding enhancement and cultivated in the regions where A. gossypii is still
considered a major concern.
Supplementary Materials: The following supporting information can be downloaded at:
www.mdpi.com/xxx/s1, Figure S1: The growth of eighteen lilies during aphid inoculation; Figure
S2: Comparison of body form of various ages and wing morphs of Aphis gossypii; Figure S3: Leaf
adaxial surface and abaxial surface of eighteen lilies; Figure S4: Leaf abaxial surface stomata of eight-
een lilies; Figure S5:
Leaf transverse sections of eighteen lilies, showing the epidermal tissues and
the palisade and spongy tissues.
Author Contributions: Conceptualization, H.S., J.Z. and Y.L. (Yilin Liang); methodology, H.S. and
Y.L. (Yilin Liang) and J.Z.; software, H.S., C.W. and L.G.; validation, H.S., P.Z. and Y.T.; formal anal-
ysis, H.S.; investigation, H.S., L.G. and C.W.; resources, M.S.; data curation, H.S., Y.L. (Yufan Lu)
and P.Z.; writing—original draft preparation, H.S.; writing—review and editing, H.S. and Y.T.;
Figure 6.
Correlation between the number of greenhouse aphids and biological parameters of lily
leaves (Pearson correlation coefficient). Color code ranges from blue = strong negative correlation
(r =
−
1) to white = no correlation (r = 0) to red = positive correlation (r = +1). Labels with “*” indicate
the significant correlations at different levels (* p≤0.05; ** p≤0.01).
4. Conclusions
As a limitation to the development of the lily industry, A. gossypii has attracted much
attention from researchers. This study evaluated the aphid resistance of eighteen lilies in
the field and greenhouse. The correlation between the number of aphids and lily leaf color
parameters, stomatal density and size, thickness of leaf layers, leaf surface wax content, and
Insects 2023,14, 936 13 of 15
leaf water content was assessed. The results show that ‘Palazzo’, ‘Nymph’ and L. lancifolium
displayed higher resistance to A. gossypii. In contrast, ‘Black Beauty’ and ‘Magnefique’
were more susceptible to A. gossypii than the other lilies. There was a significant negative
correlation between greenhouse aphid number and leaf palisade tissue thickness. The
resistant lilies ‘Palazzo’, ‘Nymph’, ‘Cameleon’, and L. lancifolium have great potential to
be used for breeding enhancement and cultivated in the regions where A. gossypii is still
considered a major concern.
Supplementary Materials:
The following supporting information can be downloaded at: https://
www.mdpi.com/article/10.3390/insects14120936/s1, Figure S1: The growth of eighteen lilies during
aphid inoculation; Figure S2: Comparison of body form of various ages and wing morphs of Aphis
gossypii; Figure S3: Leaf adaxial surface and abaxial surface of eighteen lilies; Figure S4: Leaf abaxial
surface stomata of eighteen lilies; Figure S5: Leaf transverse sections of eighteen lilies, showing the
epidermal tissues and the palisade and spongy tissues.
Author Contributions:
Conceptualization, H.S., J.Z. and Y.L. (Yilin Liang); methodology, H.S. and
Y.L. (Yilin Liang) and J.Z.; software, H.S., C.W. and L.G.; validation, H.S., P.Z. and Y.T.; formal analysis,
H.S.; investigation, H.S., L.G. and C.W.; resources, M.S.; data curation, H.S., Y.L. (Yufan Lu) and P.Z.;
writing—original draft preparation, H.S.; writing—review and editing, H.S. and Y.T.; visualization,
H.S. and Y.L. (Yufan Lu); supervision, M.S.; project administration, M.S.; funding acquisition, M.S.
All authors have read and agreed to the published version of the manuscript.
Funding:
This work was funded by the National Natural Science Foundation of China (31971708,
32271947), Beijing Natural Science Foundation (6202022), and Science, Technology & Innovation
Project of Xiongan New Area (2022XAGG0100).
Data Availability Statement:
The datasets in this study are available from the corresponding author
upon reasonable request.
Conflicts of Interest: The authors declare no conflict of interest.
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