Introduction
Cucumber
(Cucumis sativus L.) is a widespread vegetable crop worldwide (Wehner
and Guner 2004). It is grown in Egypt as a summer crop in the
open field during March to September (Alkharpotly et al. 2019). Cucumber
is a major vegetable crop with important economic and biological value (Che and
Zhang 2019). Eggplant (Solanum melongena L.) is a warm-weather crop and
one of the most prevalent vegetable crops worldwide, especially in Africa,
subtropical regions, Southeast Asia and the Middle East (FAO 2017; Chapman
2019). Eggplant fruit is a rich source of numerous nutrients, carbohydrates,
dietary fiber, protein, vitamins, essential minerals and some bioactive
compounds (Oladosu et al. 2021; Mahamad et al. 2022). Okra Abelmoschus
esculentus L. (Moench.) is one of the most common and popular summer
vegetable crops in Egypt due to its delicious taste and high nutritional value
(Abdel-Fattah et al. 2020). Okra is cultivated in tropical, subtropical, and warm
temperate climates in different countries (Durazzo et al. 2018; Islam
2019). Okra fruit has
a high moisture content, rich in nutrients, and is important source of
vitamins, minerals, proteins, carbohydrates, and lipids (Al-Shawi et al. 2020; Dantas et
al. 2021). The total cultivated area in Egypt reached 24184, 63233 and 9408
hectares (ha) in 2022 producing 593901, 1972593 and 118055 tons with an average
of 24.56, 31.18 and 12.55 tons/ha for cucumber, eggplant and okra respectively,
(Anonymous 2023).
Sucking insect pests are most notorious group of pests for agricultural
crops. Unlike most chewing insect pests, sucking insect pests cause more severe
damage to the crops (Yadav and Rathee 2020). Sucking insect pests such as
aphids, whitefly and thrips are common sucking pests of vegetables. Extensive
feeding by these pests not only results in plant damage and yield reduction,
but it also predisposes plants to various pathogens that increase the severity
of damage and crop losses (Khan et al. 2020; Rani et al. 2020).
The spider mite, Tetranychus urticae Koch is considered in
particular one of the most dangerous pests in different regions of the world
(Grbić et al. 2011;
Abad et al. 2019) and
affects a very wide range of plants. It is particularly predominant in
intensive agricultural systems and affects crops by its direct feeding (Gorman et
al. 2001). The intensive feeding of mites combined with a
rapid increase in population size has a negative effect on the physiology of
the whole plant, as well as the yield and quality (Archer and Bynum 1993;
Suekane et al. 2012). The
increase in T. urticae population and its
feeding cause leaf malformation and a web formation occurs on the plant apex
(Jakubowska et al. 2022). It
causes significant losses in the yield of many important economic crops (Salman
2007). Sucking pests are causing serious damage to agricultural
and horticultural crops by reducing their quantity and quality (Ward et al.
2002; Hassan 2009; Rani et al. 2020).
Plants differ in their degree of susceptibility to infestation and
level of damage, and this is due to many various factors, including the
morphological and chemical characteristics of the plant. Plant direct defense against
insect herbivores is involved both physical and chemical barriers which hinder
insect herbivore’s development and reproduction (Tibebu 2018). Plants have a variety of defense mechanisms
to defend themselves from pest attack, and these include structural and
chemical defenses (Pedras and Yaya 2015; Lev-Yadun 2016). Plants also use several morphological and
biochemical defenses to withstand insect herbivores (War et al. 2020).
Besides, these characteristics are also crucial for crop yield and quality,
which are fundamental criteria in selecting resistant varieties (Amin et al.
2016).
The
crops have intrinsic chemical defenses to protect themselves from pests. Improving the
capabilities of these defensive factors could have the potential to help
improve agricultural pest management (Yactayo-Chang et al. 2020).
Plant morphological
traits such as trichomes, spines and cell wall are the first defense line
against piercing-sucking insect pests and have a substantial role in plant
resistance to phytophages (Hanley et al. 2007; He et al. 2011;
War et al. 2012). Trichomes play a principal role in plant defense
against many plant pests, and that include both toxic and deterrent effects (Chamarthi et al. 2010).
Leaf characteristics may affect the preference
and activity of herbivores (Gianoli and Hannunen 2000) and then impact the
herbivore assemblages (Peeters 2002). Because there are many types of hairs on
different plant species, their defensive roles differ against plant-feeding
pests (Steinite and Ievinsh 2003).
Plant biochemical defense
mechanisms against herbivores are a wide range, highly dynamic, and affect
directly and indirectly (War et al. 2012). Defense mechanism and nutritional factor of
plant often influence the host choice and potential behavior of herbivores
(Bernays and Chapman 1994).
Therefore, the main
purpose of this work was to investigate the impact of chemical content and the
morphological characteristics of the leaves against infestation of two spotted
spider mite, aphids, whitefly and thrips on cucumber, eggplant and okra plants.
The population dynamic of these pests was also monitored.
Materials and Methods
The
field studies
The field experiment was carried
out at Ibshway, Fayoum Governorate, Egypt during summer 2021. Three different
vegetable crops: C. sativus L. (Cucurbitaceae), A. esculentus L.
(Malvaceae) and S. melongena L. (Solanaceae) were chosen for this study.
Plant
cultivation: The
growing season extended from February to June 2021. All cultivars were sown on
the same date with the same surrounding environmental conditions. The three
crops were cultivated in late February in an area around 0.20 ha divided into
three plots of about 700 m2/crop, and each plot divided into three
equal replicates using Randomized Complete Block Design. Normal agricultural
practices were followed with no pesticides applied in the entire experimental
area throughout the study period.
Population of sucking pests: The occurrence of the
phytophagous mite (T. urticae Koch (Tetranychidae), aphids (Aphididae),
whitefly {Bemisia tabaci Genn. (Aleyrodidae)} and thrips {Thrips
tabaci L. (Thripidae)} were investigated under open field conditions.
The investigation
started after three weeks from planting date (February 24, 2021). Randomly 25
leaves per replicate were taken weekly from the different plant portions
representing all cultivated area for each crop. The picked leaves were held in
separate sample bag which were properly labeled and individually examined in
the laboratory under a binocular. The number of spider mite was counted in
2.5cm2 area on the leaf lower surface according to Kumar et al.
(2015), while the number of aphids, whitefly and thrips was counted in the
whole leaf surface as described by Poe (1980).
Laboratory studies
Chemical analysis of plant
leaves to determine certain biochemical constituents: Non-infested leaf samples of
cucumber, okra and eggplant were taken and transferred to the Research Park,
Faculty of Agriculture, Cairo University for chemical analysis. Some chemical
components of leaves were determined as follows: Total carbohydrates were
extracted and estimated according to (Kostas et al. 2016). Total protein
was calorically examined by ninhydrin reagent as described by (Lee and
Takabashi 1966). Total phenols were assessed by Folin-Ciocateu method as
modulated by (Singleton and Rossi 1965). Total chlorophyll in leaf extracts was
determined colorimetrically as defined by Holden (1965).
Macro-elements
Total nitrogen was determined using
Micro-Kjeldahl method according to (A.O.A.C. 1970). Vanadomolybdate yellow
method spectrophotometrically was used to estimate Phosphorus content in plant
sample as stated by (Jackson 1973). A flame photometer was used to measure
potassium (K) content in plant leaf sample as applied by (Jackson 1973).
Scanning Electron Microscopy
(SEM) of plant leaf surface: Leaf samples of cucumber, okra and eggplant plants were
collected and scanned using a Scanning Electron Microscopy (SEM) (Joel JSM.
5200LA) at the Applied Center for Entomonematodes (ACE), Faculty of
Agriculture, Cairo University, Egypt. SEM technique was used as described in
previous studies (Karnowsky 1965; Fischer et al. 2012). Trichome and stomata measurements were determined
with the AnalySIS®3.2 software program for image analysis (Olympus-Hamburg,
Germany) and their frequency (n/mm2).
Statistical
analysis
InfoStat software package was
used to detect significant differences. Mean values of all studied variables were separated by Duncan’s
multiple range test (Duncan 1955)
(P ≤ 0.05). The significance was determined using Pearson's correlation
coefficient at P = 0.05.
Results
Population dynamics of the main
sucking pests
The data indicated the
population dynamics of certain sucking pests (spider mite, aphid, whitefly and
thrips) on three vegetable crops (cucumber, okra and eggplant) during 2021
season (Table 1).
Population of T. urticae:
The population of T. urticae was
observed on cucumber throughout the growing season. The population gradually
increased in high numbers to reach the peak at the end of the season (June 9)
with 852.0 individuals and 3325.7 eggs. The total number reached 1771.3
individuals and 10770.0 eggs.
In
contrast to infestation in cucumber, T. urticae was recorded in eggplant
and okra plants with low numbers. The total number reached 116.0 individuals and
458.7 eggs in eggplant, and less numbers were observed on okra leaves in a few
samples throughout the season and the total number recorded was 31.3
individuals and 78.3 eggs (Table 1).
Population of aphids: The population of aphids was observed in cucumber at the beginning of
the season on the 17th of March 34.7 individuals and reached the
peak 136.3 individuals at the end of March and then the population declined to reach
5.3 individuals in mid of April. Thereafter the population increased to record
115.0 individuals at the end of April and then gradually reduced to 9.0
individuals at the end of the season. The total number recorded was 676.0
individuals/season.
In okra,
aphids observed at the end of March with 5.7 individuals and progressively
increased to reach the peak 177.7 individuals on the 5th of May, then
greatly decreased to record 2.0 individuals in the 3rd week of May.
After that significantly increased to 104.3 individuals at the end of the
season. The total number reached 624.7 individuals/season. In
contrast, only few numbers of aphids were recorded in eggplant throughout the
season with total number of 35.0 individuals/season (Table 1).
Population of whitefly: The infestation of B. tabaci was observed throughout the season
in the three crops. High numbers of B. tabaci were recorded in cucumber
throughout the season, the highest number was registered in the 2nd
week of May 909.0 nymphs. The total number reached 5216.7 nymph/season. In
contrary to the population of whitefly in cucumber, low total numbers were
recorded 552.0 and 458.3 nymphs/season in eggplant and okra, respectively
(Table 1).
Population of thrips: T. tabaci was recorded with high numbers
in cucumber at the beginning of the season and recorded highest number 309.0
individuals on the 24th of March, then population gradually
decreased to record 26.0 individuals in mid April. Thereafter the population
increased with fluctuating numbers to reach 278.0 individuals at the end of the
season. The total number of T. tabaci recorded was 1707.0
individuals/season. Contrarily, few total numbers were recorded in eggplant and
okra (44.0 and 11.0 individuals/season, respectively) (Table 1).
The
relation between population of the certain piercing-sucking pests and some leaf
chemical characteristics
Table
1: Mean number
and population fluctuation of certain sucking pests on cucumber, okra and
eggplant plants during Summer season, 2021
|
Crop |
Pest |
Sampling date |
Total |
Average |
|||||||||||||
|
17/03/2021 |
24/03/2021 |
31/03/2021 |
07/04/2021 |
14/04/2021 |
21/04/2021 |
28/04/2021 |
05/05/2021 |
12/05/2021 |
19/05/2021 |
26/05/2021 |
02/06/2021 |
09/06/2021 |
|||||
|
|
|
No. of pest/25 leaves |
|
|
|||||||||||||
|
Cucumber |
T. urticae |
M. stages |
8.3 |
5.0 |
36.0 |
25.0 |
7.3 |
17.0 |
61.7 |
30.0 |
84.7 |
105.0 |
124.0 |
415.3 |
852.0 |
1771.33 |
136.26 |
|
Eggs |
25.7 |
32.3 |
112.0 |
171.7 |
47.3 |
136.7 |
290.3 |
222.0 |
847.7 |
1173.7 |
1958.0 |
2427.0 |
3325.7 |
10770.00 |
828.46 |
||
|
Aphid sp. |
34.7 |
5.3 |
136.3 |
34.0 |
5.3 |
33.7 |
115.0 |
112.7 |
45.7 |
66.3 |
53.0 |
25.0 |
9.0 |
676.00 |
52.00 |
||
|
B. tabaci |
39.0 |
158.0 |
115.3 |
123.7 |
144.0 |
107.0 |
279.0 |
333.3 |
909.0 |
632.7 |
783.3 |
894.0 |
698.3 |
5216.67 |
401.28 |
||
|
T. tabaci |
146.0 |
309.0 |
149.7 |
106.7 |
26.0 |
27.3 |
76.3 |
63.0 |
168.3 |
70.3 |
162.7 |
123.7 |
278.0 |
1707.00 |
131.31 |
||
|
Okra |
T. urticae |
M. stages |
1.7 |
1.0 |
6.3 |
6.0 |
0.7 |
1.7 |
1.0 |
4.7 |
0.0 |
1.3 |
0.7 |
3.3 |
3.0 |
31.33 |
2.41 |
|
Eggs |
2.3 |
5.7 |
16.7 |
11.7 |
0.0 |
0.7 |
4.7 |
26.0 |
0.0 |
3.7 |
1.0 |
5.0 |
1.0 |
78.33 |
6.03 |
||
|
Aphid sp. |
0.7 |
0.0 |
5.7 |
3.0 |
14.0 |
24.0 |
139.0 |
177.7 |
6.0 |
2.0 |
85.3 |
63.0 |
104.3 |
624.67 |
48.05 |
||
|
B. tabaci |
25.7 |
23.0 |
32.0 |
43.3 |
12.0 |
11.0 |
45.3 |
63.0 |
36.7 |
51.7 |
48.0 |
35.3 |
31.3 |
458.33 |
35.26 |
||
|
T. tabaci |
0.3 |
2.7 |
0.7 |
0.7 |
0.3 |
2.0 |
0.0 |
1.0 |
1.0 |
0.7 |
0.7 |
0.0 |
1.0 |
11.00 |
0.85 |
||
|
Eggplant |
T. urticae |
M. stages |
2.0 |
12.0 |
10.3 |
4.7 |
14.0 |
9.0 |
8.7 |
1.0 |
5.7 |
4.3 |
5.3 |
9.3 |
29.7 |
116.00 |
8.92 |
|
Eggs |
7.3 |
20.3 |
42.0 |
10.7 |
62.7 |
57.0 |
17.7 |
0.7 |
20.3 |
23.0 |
19.0 |
35.0 |
143.0 |
458.67 |
35.28 |
||
|
Aphid sp. |
0.3 |
7.3 |
1.7 |
0.7 |
0.3 |
5.3 |
1.0 |
5.3 |
7.7 |
4.0 |
0.0 |
0.0 |
1.3 |
35.00 |
2.69 |
||
|
B. tabaci |
23.0 |
67.3 |
60.0 |
76.0 |
67.3 |
47.7 |
23.7 |
24.0 |
55.3 |
35.3 |
25.3 |
34.0 |
13.0 |
552.00 |
42.46 |
||
|
T. tabaci |
2.0 |
3.7 |
11.7 |
1.7 |
3.7 |
2.7 |
3.0 |
1.3 |
2.7 |
3.3 |
2.3 |
4.7 |
1.3 |
44.00 |
3.38 |
||
Table 2:
Mean ± SD of certain sucking pests in cucumber, okra and eggplant plants during
2021 season
|
Plant sample |
Pest species |
||||
|
T. urticae |
Aphid spp |
B. tabaci |
T. tabaci |
||
|
Individuals |
Eggs |
||||
|
Cucumber |
1771.33a ± 197.64 |
10770.0a ± 812.62 |
676.00a ± 90.70 |
5216.67a ± 355.17 |
1707.00a ± 218.17 |
|
Okra |
31.33b ± 6.66 |
78.33b ±10.50 |
624.67b ± 57.57 |
458.33b ± 75.66 |
11.00b ± 5.57 |
|
Eggplant |
116.00b ± 27.62 |
458.67b ± 66.88 |
35.00b ± 7.00 |
552.00b ± 77.70 |
44.00b ± 13.45 |
|
ANOVA 5% |
** |
** |
** |
** |
** |
Means
with the same letter not significant (P ≤ 0.05) using Duncan Multiple Range Test
(**)
highly significant
Table 3:
Mean ± SD of some leaf chemical characteristics in cucumber, okra and eggplant plants
during 2021 season
|
Plant sample |
Leaf chemical characteristics |
||||||
|
|
Total chlorophyll mg/Kg |
Total protein% |
Total carbohydrates g/100 g |
Total phenols g/100 g |
N% |
P% |
K% |
|
Cucumber |
32.26b ± 0.44 |
11.11c ± 0.11 |
3.79c ± 0.14 |
0.04b ± 0.005 |
2.12a ± 0.04 |
0.34a ± 0.04 |
1.09a ± 0.03 |
|
Okra |
46.72a ± 0.42 |
17.33b ± 0.12 |
4.82b ± 0.17 |
0.03c ± 0.004 |
3.23b ± 0.08 |
0.23b ± 0.04 |
0.83c ± 0.05 |
|
Eggplant |
31.54b ± 0.46 |
19.24a ± 0.16 |
8.10a ± 0.11 |
0.06a ± 0.003 |
3.79c ± 0.19 |
0.27ab ± 0.02 |
1.62b ± 0.05 |
|
ANOVA 5% |
** |
** |
** |
** |
** |
ns |
** |
Means with the different letters
are significant (P ≤ 0.05)
using Duncan Multiple Range Test
(**) highly
significant, (ns) no significant
The
data in Table 2 reveal the relationship between the pest population density and
the plant type. Table 3 shows the relationship among the biochemical
constituents (total chlorophyll mg/kg, total protein%, total carbohydrates g/100 g, total phenols g/100 g,
N%, P% and K%) and
plant type. These results are described as follows:
The mean number of T. urticae
(mobile stages & eggs) on cucumber 1771.33 and
10770.00 was significantly higher than those recorded in eggplant and okra
116.00 & 458.67 and 31.33 & 78.33, respectively
(Table 2). Highly negative correlation (r =
-0.60 and -0.95) was found between T. urticae (mobile
stages and eggs) and the highest value of total chlorophyll 46.72 mg/kg in okra, while positive relation (0.75 and 0.58) was found in cucumber
(Table 4). Non-significant positive correlation (0.01 and 0.23) was found
between T. urticae and the ratio of total carbohydrates in cucumber, whilst this correlation was
negative (-0.63 and -0.37) in eggplant. Otherwise, highly negative
relation (-0.85 and -0.72) and (-98 and -99) was
recorded with P 0.34, 0.27 & 0.23% in cucumber and eggplant, respectively,
however this correlation was positive (0.16 and 0.99) in okra. Furthermore, the
population of T. urticae (moving stages) was negatively correlated
(-0.80 and -0.50) with the ratios of K and N 0.83 and 3.23% in okra
respectively, but this correlation was positive (0.30 and 0.65) with eggs of
T. urticae.
The lowest
mean number of aphids recorded with eggplant 35.0 that positively correlated
(0.10) with the lowest value of total chlorophyll 31.54 mg/Kg. Highly significant
negative correlation (-0.95 and -1.00) was found between the population of Table 4: The correlation between the pest
population and leaf chemical and morphological characteristics in cucumber,
okra and eggplant plants
|
Plant |
Cucumber |
Okra |
Eggplant |
||||||||||||
|
Pest |
T. urticae |
Aphid sp. |
B. tabaci |
T. tabaci |
T. urticae |
Aphid sp. |
B. tabaci |
T. tabaci |
T. urticae |
Aphid sp. |
B. tabaci |
T. tabaci |
|||
|
Leaf characteristic |
Mobile stages |
Eggs |
Mobile stages |
Eggs |
Mobile stages |
Eggs |
|||||||||
|
Total carbohydrates |
+ 0.01 |
+0.23 |
+0.65 |
+0.36 |
+0.82 |
−0.02 |
−0.95 |
−0.51 |
−0.67 |
+0.60 |
−0.63 |
−0.37 |
−0.11 |
+0.13 |
−0.50 |
|
Total phenols |
+0.07 |
+0.29 |
+0.70 |
+0.42 |
+0.85 |
−0.61 |
+0.55 |
+0.94 |
+1.00 |
−0.97 |
−0.67 |
−0.86 |
−0.97 |
−1.00 |
−0.78 |
|
Total chlorophyll |
+0.75 |
+0.58 |
+0.14 |
+0.47 |
−0.10 |
−0.60 |
−0.95 |
+0.09 |
−0.24 |
+0.02 |
+0.62 |
+0.35 |
+0.10 |
−0.15 |
+0.48 |
|
Total protein |
−0.52 |
−0.70 |
−0.95 |
−0.79 |
−1.00 |
+0.30 |
+1.00 |
+0.25 |
+0.56 |
−0.36 |
−0.80 |
−0.94 |
−1.00 |
−0.99 |
−0.89 |
|
N |
−0.29 |
−0.49 |
−0.84 |
−0.60 |
−0.95 |
−0.50 |
+0.65 |
+0.89 |
+0.99 |
−0.93 |
−0.79 |
−0.94 |
−1.00 |
−0.99 |
−0.88 |
|
P |
−0.85 |
−0.72 |
−0.31 |
−0.62 |
−0.07 |
+0.16 |
+0.99 |
+0.39 |
+0.67 |
−0.49 |
−0.98 |
−0.99 |
−0.93 |
−0.81 |
−1.00 |
|
K |
−0.73 |
−0.86 |
−1.00 |
−0.92 |
−0.98 |
−0.80 |
+0.30 |
+1.00 |
+0.97 |
−1.00 |
−0.96 |
−0.83 |
−0.65 |
−0.45 |
−0.90 |
|
Trichome density |
+0.92 |
+0.98 |
+0.96 |
+1.00 |
+0.86 |
−0.98 |
−0.52 |
+0.71 |
+0.44 |
−0.63 |
+1.00 |
+0.92 |
+0.79 |
+0.62 |
+0.97 |
|
Trichome length |
−0.37 |
−0.15 |
+0.32 |
−0.02 |
+0.54 |
−0.97 |
−0.09 |
+0.95 |
+0.80 |
−0.91 |
+0.57 |
+0.30 |
+0.04 |
−0.21 |
+0.43 |
|
Trichome thickness |
+0.08 |
−0.14 |
−0.58 |
−0.27 |
−0.76 |
−0.31 |
+0.80 |
+0.77 |
+0.93 |
−0.83 |
−0.77 |
−0.93 |
−0.99 |
−0.99 |
−0.86 |
|
Stomatal density |
−0.12 |
+0.11 |
+0.56 |
+0.24 |
+0.74 |
+0.22 |
−0.85 |
−0.70 |
−0.90 |
+0.78 |
+0.73 |
+0.49 |
+0.25 |
+0.01 |
+0.61 |
|
Stomatal aperture area |
−0.77 |
−0.89 |
−1.00 |
−0.95 |
−0.97 |
+0.36 |
+1.00 |
+0.19 |
+0.50 |
−0.30 |
−0.06 |
+0.25 |
+0.49 |
+0.69 |
+0.11 |
|
Stomatal dimension length |
+0.97 |
+0.89 |
+0.58 |
+0.82 |
+0.37 |
−0.74 |
−0.88 |
+0.27 |
−0.06 |
−0.16 |
+0.11 |
−0.20 |
−0.44 |
−0.65 |
−0.05 |
|
Stomatal dimension width |
−0.10 |
−0.32 |
−0.72 |
−0.44 |
−0.87 |
+0.22 |
−0.85 |
−0.70 |
−0.90 |
+0.78 |
−0.94 |
−1.00 |
−0.98 |
−0.89 |
−0.98 |
Correlation coefficient: (+) positive correlation; (‐) negative correlation
aphids
and the ratios of total protein 11.11 and 19.24% in cucumber and eggplant
respectively, while the population was positively correlated (0.25) with the total protein 17.33% in okra. For the correlation
between the aphid population and total carbohydrates 4.82, 8.10 and 3.79 g/100 g was negative (-0.51 and -0.11) in okra and eggplant, however was
positive (0.65) in cucumber, respectively
(Tables 3 and 4). Highly significant positive correlation (0.94 and 0.70) was
reported between the aphid population and the total phenols 0.03 and 0.04 g/100 g in okra and cucumber,
respectively. Correspondingly, a highly significant negative
correlation (-0.97) was investigated with
the highest value of total phenols 0.06 g/100 g in eggplant. On the other hand, strong negative correlation
was found between the aphid population and the ratios of N, P and K (-0.84, -0.31 and -1.00) and (-1.00, -0.93 and -0.65) in cucumber and eggplant, respectively. On contrast,
positive correlation
with N, P and K (0.89, 0.39 and 1.00) was registered in okra, respectively (Table 4).
The B.
tabaci infestation was observably higher in cucumber with mean number
5216.67 than in eggplant and okra 552.00 & 458.33, respectively (Table 1). A
positive relationship (0.36 & 0.13) was found between B. tabaci and
the value of total carbohydrates in cucumber and eggplant respectively, while
this relation was negative (-0.76) in okra (Table 4).
Negative
relation (-0.24 & -0.15) was found between B. tabaci and the total
chlorophyll in okra and eggplant, respectively, however this relation was
positive (0.47) in cucumber. Similarly, considerable negative relationship was
observed with N, P and K (-0.60, -0.62 & -0.92) and (-0.99, -0.81 &
-0.45) in cucumber and eggplant, respectively. On contrary, this relation was
highly positive with N, P and K (0.99, 0.67 & 0.97) in okra, respectively
(Table 4).
The
correlation between T. tabaci population and the values of each of total
protein, carbohydrates, phenols, N, P and K was negative (-0.89, -0.50,
-0.78, -0.88, -1.00, and -0.90), while was positive (0.48) with total
chlorophyll in eggplant, respectively. Also in cucumber, negative relationship
was found with protein, N, P, K and chlorophyll (-1.00, -0.95, -0.07, -0.98 and
-0.10), but was positive with carbohydrates and phenols (0.82 and 0.85),
respectively. Likewise, negative relation was obtained in okra with the ratios
of protein, phenols, N, P and K (-0.36, -0.97, -0.93, -0.49 and -1.00), whilst
was positive with carbohydrates and chlorophyll (0.60 and 0.02), respectively
(Table 4).
The relation between population
of the certain piercing-sucking pests and some leaf morphological characters
The relation between the
population of piercing-sucking pests and certain leaf morphological traits
(trichomes and stomata) is elucidated in Tables (1 and 4). The morphology of
leaf hairs is photographed using SEM as illustrated in (Fig. 1, 2 and 3).
Trichome density
7.20, 4.89 and 4.49 no/mm2, trichome length 470.06, 461.96 and
370.18 µm, and stomatal density 569.80, 321.68 and 239.39 no./mm2 in
cucumber higher than in eggplant and okra, respectively. Hence, T. urticae,
B. tabaci and Thrips tabaci infestation in cucumber was
significantly higher than in eggplant and okra (Table 5).
Moreover, high
significant positive relationship was found between T. urticae (mobile
stages and eggs) and each of the trichome density (0.92 and 0.98) and stomatal
length (0.97 and 0.89), while negative relation was recorded with trichome
length (-0.37 and -0.15) and stomatal dimension width (-0.10 and -0.32) in cucumber,
respectively. On contrast, negative
correlation was observed with trichome density (-0.98 and -0.52) and stomatal length
(-0.74 and -0.88) in okra, respectively. In
eggplant, the population of T. urticae positively correlated with
trichome density (1.00 and 0.92) and trichome length (0.57 and 0.30), while was
negatively correlated with stomatal dimension width (-0.94 and -1.00),
respectively (Table 4).
For aphids on
cucumber, highly positive correlation was found with trichome density, stomatal
density and stomatal dimension length (0.96, 0.56 and 0.58), while was highly
negative with trichome thickness, stomatal aperture area and stomatal dimension
width (-0.58, -1.00 and -0.72), respectively. In okra, this correlation was
positive with trichome density, stomatal dimension length, trichome thickness
and stomatal aperture area (0.71, 0.27, 0.77 and 0.19), but was negative with
stomatal density and stomatal dimension width (-0.70 and -0.70), respectively.
In eggplant, the population of aphids positively correlated with trichome
density, stomatal density and stomatal aperture area (0.49, 0.25 and 0.49),
whilst was negatively correlated with stomatal dimension length, trichome
thickness and stomatal dimension width (-0.44, -0.99 and -0.98), respectively
(Table 4).
Table 5: Mean ± SD of some
leaf morphological characteristics in cucumber, okra and eggplant plants during 2021
season
|
Plant sample |
Leaf morphological
characteristics (± SD) |
||||||
|
|
Trichome density (no/mm2) |
Trichome length (µm) |
Trichome thickness (µm) |
Stomatal density (no./mm2) |
Stomatal aperture area |
Stomatal dimensions (length; µm) |
Stomatal dimensions (width; µm) |
|
Cucumber |
7.20a ± 0.83 |
470.06a ± 32.51 |
75.44b ± 0.60 |
569.80a ± 71.23 |
19.76a ± 5.77 |
12.87b ± 0.34 |
10.26c ± 1.27 |
|
Okra |
4.49b ± 0.56 |
370.18b ± 34.49 |
93.91ab ± 10.67 |
239.39b ± 41.46 |
28.17a ± 9.32 |
15.20b ± 0.81 |
11.36b ± 0.53 |
|
Eggplant |
4.89b ± 0.68 |
461.96a±23.83 |
100.34a ± 7.76 |
321.68b ± 44.82 |
13.01a ± 1.33 |
27.34a ± 3.44 |
16.11a ± 0.52 |
|
ANOVA 5% |
* |
* |
ns |
** |
ns |
** |
** |
Means with the different letters
are significant (P ≤ 0.05)
using Duncan Multiple Range Test
(**)
highly significant, (*) significant, (ns) no significant
%20383-392_files/image002.jpg)
Fig. 1:
Scanning electron micrographs on the abaxial leaf epidermis (lower surface) of cucumber (Cucumis sativus L.). (A, B)
simple hairs (straight trichomes), (C)
simple hairs (appressed trichomes), (D)
stomata
%20383-392_files/image004.jpg)
Fig. 2:
Scanning electron micrographs on the abaxial leaf epidermis (lower surface) of okra (Abelmoschus esculentus
L.). (A) simple hairs
(trichomes with pedestal), (B)
appressed stellate trichomes,
(C) sessile trichomes, (D) stomata
%20383-392_files/image006.jpg)
Fig. 3: Scanning electron micrographs
on the abaxial leaf epidermis (lower surface) of eggplant (Solanum melongena
L.). (A, B, C) appressed stellate
trichomes, (D) stomata
For B. tabaci,
also in cucumber positive relation was recorded with trichome density, stomatal
density and stomatal dimension length (1.00, 0.24 and 0.82), and was negative
with trichome thickness, stomatal aperture area and stomatal dimension width
(-0.27, -0.95 and -0.44), respectively. The relation differed in okra whereas
was positive with trichome density, trichome thickness and stomatal aperture
area (0.44, 0.93 and 0.50), nevertheless was negative with stomatal density,
stomatal dimension length and stomatal dimension
width (-0.90, -0.06 and -0.90),
respectively. Similarly, different correlations were observed in eggplant
whereas the population was positively correlated with trichome density,
stomatal density and stomatal aperture area (0.62, 0.01 and 0.69), yet was
negatively correlated with stomatal dimension length, trichome thickness and
stomatal dimension width (-0.65, -0.99 and -0.89), respectively (Table 4).
For T. tabaci
on cucumber, comparable as formerly mentioned with aphids and B. tabaci,
the correlation was positive with trichome density, stomatal density and
stomatal dimension length (0.86, 0.74 and 0.37), however was negative with
trichome thickness, stomatal aperture area and stomatal dimension width (-0.76,
-0.97 and -0.87), respectively. Otherwise in okra, the population was
positively correlated with stomatal density and stomatal dimension width (0.78 and
0.78), but was negatively correlated with trichome density, stomatal dimension
length, trichome thickness and stomatal aperture area (-0.63, -0.16, -0.83 and
-0.30), respectively. Furthermore, in eggplant the relationship was positive
with trichome density, stomatal density, trichome length and stomatal aperture
area (0.97, 0.61, 0.43 and 0.11), yet was negatively correlated with stomatal
dimension length, trichome thickness and stomatal dimension width (-0.05, -0.86
and -0.98), respectively (Table 4).
In
general, highly significant positive correlation was obtained between the
population of aphids, whitefly and thrips with trichome density in cucumber,
while this correlation was highly significant negative with stomatal aperture
area. Also in eggplant, there was a significant positive correlation between
these insect pests and trichome density; however, this correlation was
significantly negative with trichome thickness and stomatal dimension width. As
for okra, these pests differed in their correlation with each of the
morphological features (Table 4).
Discussion
Cucumber,
okra and eggplant significantly varied in their infestation with the different
sucking pests. The highest numbers of two spotted spider mite T. urticae
was obtained in cucumber plants during June and its increase was associated
with an increase in temperature. Mustafa and Al Mallah (2021) mentioned that heat
and humidity are suitable for growth and reproduction of mites.
In this study, the highest numbers of aphids were
recorded in cucumber and it coincides with the findings of Bayoumy et al.
(2017), who indicated that squash plants harbored higher numbers of Aphis
spp.
The population of Thrips tabaci was
greatly higher in cucumber than in eggplant and okra, and the highest number
was recorded during March. Comparable result was obtained in previous studies
in which, by who reported that T. tabaci population on onion plants was
peaked in February, March and April (Hendawy et al. 2011; El-Fakharany et
al. 2012).
It is well known that high
levels of K can reduce the volume of accumulated amino acids, that can decrease
sucking pest infestation (Jansson and Ekbom 2002; Leite et al. 2011). Thus, we found a negative relationship between the number of
aphids and the highest ratio of K. However, this is in contrast with the
findings of Bayoumy et al. (2017) who found a positive correlation between
the population of Aphis spp and the higher values of total proteins,
carbohydrates and N in squash plants.
Our results revealed that the spider mite T.
urticae infested cucumber plants greatly more than okra 1771.3 and 31.3
individuals that may be due to phenolic content 0.04 and 0.03 g/100 g in
cucumber and okra, respectively. This may be due to the
higher ratios of carbohydrates, protein, nitrogen and phenols, despite
the negative correlation between mites and these components,
in eggplant leaves. Similarly, Helmi and Rashwan (2015) demonstrated a
negative relationship between the infestation of sucking insects and phenol
content in some solanaceous cultivars. Further, Kielkiewicz and Vrie (1990)
mentioned that phenolic compounds have been pointed out as an important factor
mediating plant resistance to spider mites.
Population density of T. tabaci was
significantly higher in cucumber plants, that were positively related with
total phenols and carbohydrates, while it was negatively related with total protein
and nitrogen. Similar findings were reported by El-Fakharany and Knany (2018)
who pointed out positive correlation between population density of T. tabaci
and each of chlorophyll content, total phenols and P. However, this correlation
was negative with total protein, N and K. These results are supported by the
findings of Wahyuni et al. (2021) who indicated that some chemical
compounds gave a significant negative correlation with feeding damage by thrips
in Gladiolus varieties.
Okra leaves contained a higher ratio of chlorophyll
than cucumber and eggplant, that may due to vegetation type, growth nature and
plant composition. El-Fakharany and Knany (2018) suggested that the high
chlorophyll content in lettuce may cause the nature shading of lettuce leaf
growth compared to the other crops which have low chlorophyll content.
Moreover, in regard to the chlorophyll content in
okra and eggplant, the population of aphids and T. tabaci was positively
correlated with total chlorophyll, while a negative correlation was found with B.
tabaci. This finding is confirmatory with Elanchezhyan
et al. (2008) who reported that the total chlorophyll was positively
correlated with plant injury caused by aphids. Total protein in cucumber and
eggplant showed negative correlation with aphid and B. tabaci
population, while this correlation was positive in okra. This result is
contradictory to Hegab et al. (2014) who mentioned that the B. tabaci
population was positively correlated with proteins in eggplant varieties.
Furthermore, the mite infestation in okra and
eggplant was positively correlated with all chemical characteristics measured,
except only total chlorophyll in eggplant, and protein and P in okra. Ali et
al. (2015) revealed that the correlation between the mite infestation and
total carbohydrates was positive; however, it was negative with total carotenes
in five tomato hybrids. Kamel et al. (2019) reported
that the mite population was positively related with total carbohydrates and
nitrogen, but the relation was negative with total phenols in pea leaves, while
Abdallah et al. (2018) indicated a significant positive correlation
between T. urticae infestation and total phenol, while a significant
negative correlation was recorded with total protein, chlorophyll and
carbohydrates in three squash cultivars. Comparable results
were obtained in previous studies in which the correlation between sucking pests
infestation and biochemical leaf components was positive or negative in
different crops (Khan et al. 2015; Kharbangar et al. 2015; Shah et
al. 2016).
Plant morphological factors often affect the
mechanisms of pest locomotion, feeding, digestion and oviposition (Kumar 1984).
Our findings clearly showed that leaf morphological traits significantly
affected the population density of considered pests. For example, from the
results obtained, these pests had a positive relation with trichome density and
stomatal density, while had a negative relation with trichome thickness and
stomatal dimension width in cucumber and eggplant. For okra, trichome (density,
length and thickness) positively affected the population of aphids and B.
tabaci, however it negatively affected the population of T. tabaci
and T. urticae. Stomatal density and stomatal dimension width negatively
affected the population of aphids and B. tabaci, while it positively
affected the population of T. tabaci and T. urticae. These
results corroborate the findings of El-Samahy and Saad (2010) who stated the
high significant positive correlation between leaf trichome density and
population of T. urticae and B. tabaci, while negative
correlation was recorded with A. gosssypii in three soybean varieties.
Similarly, Abdallah et al. (2018) noted a positive correlation between
mite population and leaf trichome density in three squash cultivars.
Identically results were obtained by Hasanuzzaman
et al. (2016) who stated that the number of whitefly was positively correlated
with leaf trichome density and length in different varieties of eggplant.
Similarly, Harish et al. (2023) indicated that the leaf trichome density
and trichome length showed a significant positive correlation with the whitefly
population on soybean genotypes. Consequently, leaves having lower trichome
density considered more resistance against B. tabaci infestation
(Ayyasamy and Baskaran 2005). In addition, whitefly population was positively
correlated with trichome length in eggplant (Singh et al. 2002; Hasanuzzaman
et al. 2016), and beans (Oriani et al. 2005).
Conclusion
Although cucumber leaves contained the lowest ratios of
proteins, carbohydrates and nitrogen, were highly infested with all the
investigated pests. This may be due
to some leaf morphological
traits such as trichome density, trichome length and stomatal density. It can
be concluded that neither the chemical components nor the morphological
characteristics alone can always be the main reason for the susceptibility or
resistance of plants against pests, but this can be attributed to more than one
of these factors. On the basis of these results, it is
possible to increase plant resistance against pests by improving the
morphological and chemical characteristics of plants using advanced
agricultural technology and by developing resistant plant varieties.
Author
Contributions
HSA
planned the experiments, HSA and MAR interpreted the results and made the write
up, HSA and IAA statistically analyzed the data and made illustrations.
Conflicts
of Interest
All
authors declare no conflicts of interest.
Data
Availability
Data
presented in this study will be available on a fair request to the
corresponding author.
Ethics
Approval
Not
applicable in this paper
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