Studies on Inducer Mediated Resistance Responses
against Biological Fitness of Brevicoryne brassicae (Homoptera: Aphididae) on Brassica napus
Muhammad
Wajid Javed1*, Mansoor ul Hasan1, Muhammad Sagheer1
and Shahbaz Talib Sahi2*
1Department
of Entomology, University of Agriculture, Faisalabad, 038000, Pakistan
2Department
of Plant Pathology, University of Agriculture, Faisalabad 038000, Pakistan
*For correspondence: shahbazsahi@uaf.edu.pk; muhammadwajidjaved@gmail.com
Received 09 July 2020; Accepted 04 September 2020;
Published 10 December 2020
Abstract
Cabbage
aphid, Brevicoryne brassicae is among
the notorious insect pests of Canola (Brassica
napus) and other Brassica spp., with a reported loss of up to 75%. It
has gained resistance against conventional chemical insecticides. So, to
activate inducer mediated plant resistance is among the workable solutions
against this pest. Henceforth, inducer-mediated resistance based on categorizes
of induced-resistance (IR), nutrient-deterrence (ND) and sulphur-integration
(SI), was applied in 18 treatments. Their responses against aphid development
period, reproduction time, progeny production, immature becoming adults,
percent survival and mortalities, were noted-down. In the IR category, all the
biological parameters were affected
significantly by 1 mM (1 and mM should be in the same line) mM
salicylic acid-T4 treatment, whereas in ND, silicon 50 kg ha-1-T10
was more effective. Likewise, during SI studies, bio-sulphur-T15 remained an
efficient one. Overall, the developmental period of B. brassicae nymphs was delayed by T10 (Si 50 kg ha-1),
followed by T4 (1 mM SA), while Compost-T16 expedited their development.
Besides these, reproduction time was reduced at the most by T4, followed by
T15. Aphid progeny production was again decreased significantly by T4 and T10,
while T16 (Compost) presented the maximum progenies. Associatively, the least
number of nymphs becoming adults were shown in T4, T10 followed by T7 (1 mM
CA). The highest percent nymph survival was shown in T1 (control) and T16
(compost) with the highest nymph percent mortality in T4 and T7. Hence,
salicylic acid, silicon, and bio-sulphur showed maximum effective resistance
responses but in concentration-dependent manner. These findings can be used in
future integrated pest management programs of aphids and other specialists on
related hosts. © 2021 Friends Science Publishers
Keywords:
Ammonium
sulphate; Aphid; Bio-sulphur; Citric acid, Compost; Salicylic acid
Canola, Brassica napus L. (Brassicaceae: Brassicales) is an important oilseed crop, ranked second among the edible
oilseed in the world (Razaq et al.
2016; Kumar et al. 2017; Mohamed et al. 2020). Low contents of
anti-nutritional ingredients like erucic acid and glucosinolates have made it
worthwhile as eatable but simultaneously enhanced its vulnerability to insect
pests (Mahmoud and Osman 2015; Nouri-Ganbalani et al. 2018; Sato et al.
2019; Chew 2020). Among such insect pests, cabbage aphid or Brevicoryne brassicae (L) (Homoptera:
Aphididae) is a notorious pest causing huge yield loss. Losses are caused
directly by sucking the cell sap and indirectly by transferring different types
of viruses, which may result in complete crop failure (Saleem and Shah 2010;
Razaq et al. 2016; Kumar et al. 2017). Moreover, the pest has a
very high reproduction rate (~43 generations/year) and adaptability in changing
environmental conditions (Saleem and Shah 2010; Guilbaud and Khudr 2020; Javed
and Qiu 2020; Li et al. 2020).
Synthetic chemical insecticides have been used against this pest, which are posing severe health concerns and
also resulted in insecticide resistance development (Ahmad and Akhtar 2013; Li et al. 2020; Prince and Chandler 2020).
Moreover, the waxy cuticle of the pest also reduces the effectiveness of
applied insecticides (Ahmad and Akhtar 2013; Nouri-Ganbalani et al. 2018). This situation is
thought-provoking and demands the researchers to evaluate alternative control
measures that are safer to the environment and well-suited to human health
(Javed and Qiu 2020; Prince and Chandler 2020).
In such a situation, inducer mediated plant resistance based on
induced-resistance, nutrient-deterrence, and others, etc., are appeared to be a
safer alternative tool (Nouri-Ganbalani
et al. 2018; Santos et al. 2018;
Agathokleous et al. 2019). These may
reduce not only the insect attack but also improve the growth, yield, and vigor
of the crop (Li et al. 2020; Rizzo et al. 2020). In induced-resistance
(IR), plant bio-activators like salicylic, humic and jasmonic acids are working against insects and other stresses
(Chen et al. 2020; Khoshfarman-Borji et al. 2020; Naseem et al. 2020). Likewise, in nutrient-deterrence (ND), nutrients
that can impact insect fitness and biology, are being utilized (Teixeira et al. 2017; Agathokleous et al. 2019; Boer et al. 2019). Here, the most important one is silicon (Si) that
has also been found to be a critical in resistance induction against a variety
of sucking insect pests, especially aphids (Teixeira et al. 2017; Boer et al.
2019; Rowe et al. 2020). Recently,
ammonium sulphate (AS) has also been evaluated against herbivory on cauliflower
(Agathokleous et al. 2019).
Accordingly, sulphur-integration (in elemental-ES or bio-BS formulations with
soil amendments) against insect pests, is also needed to be evaluated due to
the role of sulphur in the generation of various anti-insect compounds in
brassica (Santos et al. 2018; Badenes-Pérez et
al. 2020).
Although salicylic acid (SA) has been explored recently against the
biological fitness of this pest on B.
napus (Khoshfarman-Borji et al.
2020), however, there is no available information on inducer mediated responses
of citric acid, ammonium sulphate and sulphur (bio/elemental formulations)
against this pest. Moreover, in this study, citric acid and bio-sulphur are
being used for the first time against any crop pest. In the main experiments,
compost and ammonium sulphate are also being utilized for the first time,
particularly against B. brassicae.
Furthermore, these inducers were chosen regarding their field doses so that
their performances can be suggested together for integrated pest and crop
nutrient management programs.
Consequently, the current study was designed to check the
responses/efficacies of these inducers against B. brassicae biological fitness comprising seven different
resistance inducers in 18 treatments. Thus, their responses against insect
development period, reproduction time, progeny production, nymphs becoming
adults, nymph percent survival, and percent mortalities were noted.
Seeds of B. napus cv. Faisal Canola were sown in
sterilized soil pots (top diameter 19 cm and height 15 cm) filled with 3 kg of
soil (sandy-clay-loam, NPK 0.05%, 7.47, and 150 ppm). Environmental conditions
were 21 ± 5ºC temperature, 65±5% RH, and photoperiod of 10:14 (L:D) h in the
screen house. Various instars of B.
brassicae were collected from Brassica crops (Brassica juncea, Brassica
napus and Brassica oleracea). The
insect culture was maintained on B. napus
hosts, for more than 15 generations, at above-mentioned conditions to
homogenize the population (Nouri-Ganbalani
et al. 2018). The experiments proceeded on plants with 5–7 expanded leaves
(Ahmed et al. 2018).
Treatments and application
Seven different resistance inducers in 18 treatments within CRD design were applied
via foliar and soil application methods, in potted plants of B. napus. Major inducer categories
assigned were, induced-resistance (IR), nutrient-deterrence (ND) and sulphur-integration
(SI) to generate plant resistance against B.
brassicae. IR was contained of salicylic acid-SA and citric acid-CA, ND had
silicon-Si and ammonium sulphate-AS. In contrast, SI experiments had
elemental/bio-sulphur-ES/BS along with compost-Cp. These treatments and related
information are presented in Table 1 and 2. For IR treatment preparation,
salicylic acid and citric acid were dissolved in 0.01% ethanol and water,
respectively, for the foliar spray to form 0, 0.5, and 1 mM solutions
(Syeed et al. 2011). In 0 mM
solution of SA and CA inducers, 0.01% ethanol and water, respectively were used.
Silicon and ammonium sulphate were added to soil at the rate of 0, 25 and 50 kg
ha-1. Elemental sulphur was applied alongside bio-sulphur and
compost, in individual and integrated/combined manners. NPK was also applied
according to the recommended field dose rate. The foliar spray was applied
manually with the help of a hand sprayer (Type: Top gun-manual, Volume: 1000 cm3).
While soil applications were made by mixing the treatments in the potting soil.
Inducer mediated resistance responses against B. brassicae
Screen
house bioassays with multiple treatments were conducted to notice inducer
mediated resistance responses against B.
brassicae. Treated plants were provided with B. brassicae adult wingless female mothers of the same age groups.
Potted plants with 5–7 expanded healthy leave, were chosen to check the
responses of applied treatments. After introducing on each plant, the female
mothers (FM1) were confined under clip cage covers (6 cm diameter with a depth
of 1.5 cm). Each clip cage was referred to as one replication, and a total of
10 clip cages/replicates were followed per treatment. Then FM1 females were
observed to lay young ones/nymphs (N1). After that, only one immature/nymph
(N1) was allowed to stand per clip cage, and rests were removed. Later on,
primary biological fitness responses were followed in sequence of developmental
period of nymphs (N1) laid by FM1, reproduction time, next progeny production
(N2), the immature becoming adults out of N2 progeny and percent survival of N2
generation with percent nymph mortality (Ahmed et al. 2018).
The developmental period was noted from first instar nymph till
maturity (adult emergence), and reproduction time was considered from the time
when the adult insects (N1) started laying young ones till the finishing of
final laying; while progeny production was noticed by counting the number of nymphs per females. Likewise,
nymphs/immature becoming adults (IBA) were the immature aphid numbers of N2
that survived till the adult stage. Their percent nymph survival was noticed by
the nymphs survived in each treatment divided by total progeny in treatment and then multiplying the outcome with 100.
Table 1: Inducer treatments and their
nature
No. |
Nature of treatments |
No. |
Nature of treatments |
T1 |
Control (Ct) |
T10 |
Silicon 50 kg ha-1 |
T2 |
0 mM
salicylic acid |
T11 |
Ammonium sulphate (AS) 0 kg ha-1 |
T3 |
0.5 mM
salicylic acid |
T12 |
Ammonium sulphate 25 kg ha-1 |
T4 |
1 mM salicylic
acid |
T13 |
Ammonium sulphate 50 kg ha-1 |
T5 |
0 mM citric acid |
T14 |
Elemental sulphur (ES) |
T6 |
0.5 mM
citric acid |
T15 |
Bio-sulphur (BS) |
T7 |
1 mM
citric acid |
T16 |
Compost (Cp) |
T8 |
Silicon 0 kg ha-1 (Si) |
T17 |
Elemental sulphur + compost |
T9 |
Silicon 25 kg ha-1 |
T18 |
Bio-sulphur + compost |
Table 2: Inducers, specifications and
suppliers
Inducers/nutrients |
Specifications |
Suppliers |
Salicylic acid |
Purity 99.0 % |
Sigma Aldrich, MO, USA |
Citric acid |
Purity 99.5 % |
Sigma Aldrich, MO, USA |
Ammonium sulphate |
Nitrogen: 21%, Sulphur: 24% |
Engro Fertilizers, Pakistan |
Silicon (SiO2) |
Silicon: 46.7%, O2: 53.3%, Purity: 99.9% |
Nanoshel, DE, USA |
Elemental sulphur |
(Bentonite) Sulphur: 90 ± 1.5%, Inert: 10 ± 1.5% |
Port Qasim, Karachi, Pakistan |
Bio Sulphur |
Sulphur: 70%, NPK: ~2.5%, 1.5%, 3% |
Dr. M. Naveed, ISES, UAF |
Compost (g kg-1) |
Carbon: 210.5, Nitrogen: 17.1, P: 3.01, pH: 6.43 |
Dr. M. Naveed, ISES, UAF |
Percent of nymph mortality was found by deducting survived insect
percent out of 100. Every observation was recorded daily until all the insects
died (Bernardi et al. 2012;
Nouri-Ganbalani et al. 2018).
Data analysis
In all
three inducer mediated resistance experiments, data of each category with
replicated ten times, were analyzed individually for IR, ND, and SI treatments.
All the responses of treatments were averaged for mean values, and Fisher
analysis was computed using the statistical software (Statistix 8.1, Analytical
Software, Tallahassee). Significant differences among treatment means were
separated by Tukey HSD test as a post-hoc parameter. Graphs were generated in
Excel (MS Office, Version 2013). Statistical significance level of P < 0.05 was taken in all assigned cases.
Statistically
significant responses (P < 0.0001)
were noticed among the induced-resistance responses for B. brassicae biological fitness (Fig. 1a–e). Insect development
period (of N1 nymphs) was delayed significantly (F6,63=14.7, P < 0.0001) by the higher
concentrations (1 mM) of both SA and CA treatments (T3 and T4 in Table
1) contrasted to T1 control. However, SA was shown to be more effective in
delaying the development to 9.96 days (P
< 0.05) compared to 8.45 days in CA (P
< 0.001; Fig. 1a). Likewise, reproduction time was also reduced the most by
SA (9.40 days) compared to the CA (10.56 days) (F6,63=12.4, P < 0.0001) (Fig. 1b). Intermediate concentrations were also efficient, but SA was
Fig. 1: Induced-resistance (IR) responses against different
biological fitness parameters of B. brassicae
a) Development period of nymphs N1
laid by females FM1 b) Reproduction
time of N1 c) Progeny production
(N2) d) Immature becoming adults
(IBA) out of N2 progeny e) Percent
survival of N2 generation
shown to be
more responsive (P < 0.001).
Other parameters like progeny production (N2 nymphs), immature becoming
adults (IBA), and N2 nymph percent survival was also disturbed (Fig. 1c–e).
Statistically significant differences were noticed for progeny (F6,63=6.90,
P < 0.0001), IBA (F6, 63=12.4,
P < 0.0001) and percent nymph
survived (F6,63=13.7, P <
0.0001). A high number of reduced progenies were observed in 1 mM SA (P < 0.0001) with 32.60 nymphs
followed by 38.70 nymphs in 1 mM CA (P
< 0.01) (Fig. 1c). Additionally, the least numbers of IBA were seen in
similar treatments with 14.60 and 20.52 nymphs compared to control (55.10
nymphs). However, the difference among IR treatment means for IBA was
non-significant (Fig. 1d). Percent nymph survival (Fig. 1e) was also appeared
to be reduced to 44.62 and 52.97% in these treatments (P < 0.001) but again values of survived B. brassicae nymphs were not much different statistically in both T4 (1 mM
SA) and T7 (1 mM CA)
treatments (Table 1). Other treatments were less
effective, depending upon their concentrations (T3 and T6) with
significance at P < 0.05, P < 0.01, when compared to the
control T1 B. napus plants (P < 0.05). Additionally, nymph
mortality was higher than 55.38% in T4 (1 mM SA) followed by 47.03% in
T7 (1 mM CA), 39.76% in T3 (0.05 mM SA) and 26.81% in T6 (0.05 mM CA), respectively (Fig. 4).
Fig. 2: Nutrient-deterrence (ND) responses
against different biological fitness parameters of B. brassicae a) Development period of nymphs N1 laid by females FM1 b) Reproduction time of N1 c) Progeny production (N2) d) Immature becoming adults (IBA) out
of N2 progeny e) Percent survival of
N2 generation.
Fig. 3: Sulphur-integration (SI) against different biological fitness
parameters
of B. brassicae a) Development period of nymphs N1 laid by females FM1 b) Reproduction time of N1 c) Progeny production (N2) d) Immature becoming adults (IBA) out
of N2 progeny e) Percent survival of
N2 generation
Nutrient-deterrence (ND)
responses against B. brassicae
Fisher
variance values revealed significant difference among nutrients (silicon and
ammonium sulphate at 0, 25 and 50 kg ha-1)
treatments to influence and retard B.
brassicae development, reproduction time, progeny
Fig. 4: Inducer mediated percent nymph mortality
responses against B. brassicae.
Series-1 (white bars) from top to bottom showing CA, AS, ES, ES + Cp, and Ct
(Control) treatments. Series-2 (dark grey bars) from top to bottom are showing
SA, Si, BS, BS + Cp, and Cp treatments. Henceforth a horizontal bar chart is generated showing the
comparisons of applied concentrations and doses as (left to right) SA vs. CA (in IR), Si vs. AS (in ND), and BS vs.
ES (in SI) responses
production (nymphs/female), IBA and nymph survival (F6,
63=28.6, 16.1, 6.94, 16.7 and 20.5) with P < 0.0001 (Fig. 2a to 2e). In the ND category, doses and their
responses remained efficient to increase the development period (N1 nymphs)
(Fig. 2a) and decrease reproduction times (Fig. 2b). Si was recorded,
apparently, more efficient to retard B.
brassicae development by delaying to 10.90 days in T10 Si-50 kg ha-1
contrasting AS treatments (7.68 days in T12, AS-25 kg ha-1). Higher
ammonium sulphate (T13, AS-50 kg ha-1) dose was inefficient and
reduced the development time to 7.56 days compared to control 7.66 days.
Associatively, reproduction time continued to vary non-significantly and
reduced by Si to 10.53 days in T10 and 10.28 days in T13, comparing against
13.55 days in T1 (Fig. 2d). While progeny production and immature becoming
adults (IBA) were 34.10 in T10 to 50.30 nymphs in T12, contrasting to IBA
numbers of 17.95 and 35.04 in the treatments of 50 kg ha-1 silicon
and 25 kg ha-1 ammonium sulphate, respectively (Fig. 2c–d). Also,
nymph survival was reduced proficiently under both treatments as Si (53.33% in
T10) and AS (69.62% in T12), with statistical significance of P < 0.05 and P < 0.01 (Fig. 2e). Maximum nymph mortality (Fig. 4), was
noticed in 50 kg ha-1 silicon and 25 kg ha-1 ammonium
sulphate with 46.67 and 30.38%, respectively.
Sulphur-integration (SI) responses against B. brassicae
Insect
development (F5,54=13.2, P
< 0.0001) and reproduction time (F5,54=11.7, P < 0.0001) was retarded efficiently by all the treatments (Fig.
3–b). However, compost (T16) was shown to work negatively to reduce aphid
development to 6.63 days and increase the reproduction time to 59.60 days.
Effective responses for development were shown by bio-sulphur treatments (T15
and T18) with 9.10 and 8.84 days against reproduction time of 9.96 and 11.33,
respectively.
Number of nymphs/female (progeny) (F5,54 =3.64, P=0.0066)
and IBA values (F5,54 =11.7, P
< 0.0001) were 41.70 (BS) and 45.80 (ES) nymphs, whereas 26.72 (BS) and
32.64 (ES) immature were transferring to adult stages. Among all such treatment
means of SI, non-significant responses (P= 0.05) were noted. However, nymph
survival (F5,54 =33.9, P <
0.0001) was observed higher in T16 (Cp) to 79.81% and lower in T15 (BS)
treatments to 64.10%. However, a significant difference among treatment means
was observed at P < 0.05 (for BS),
P<0.01 (ES and BS + Cp), and P < 0.001 (ES + Cp and BS + Cp),
respectively. Mortality percent of N2 nymphs remained higher to 35.90% in
BS-T15 and 30.24% in BS + Cp (T18) sulphur-integration treatments (Fig. 4).
While discussing mean values obtained in the SI category, all the applied
treatments were useful; however, integration of sulphur with compost exhibited
greater impacts compared to single ones.
Inducer
mediated resistance responses against insect pests have been shown as an
alternative tool to synthetic insecticides (Nouri-Ganbalani et al. 2018; Serteyn et al.
2020). In the current study, inducer mediated plant resistance, centered on
induced-resistance, nutrient-deterrence, and sulphur-integration, has shown its
tremendous potential to mitigate aphid pest as a nontoxic substitute (Teixeira et al. 2017; Agathokleous et al. 2019; Khoshfarman-Borji et al. 2020). For the first time,
citric acid, ammonium sulphate, bio-sulphur, and
compost have been recorded for their anti-insect potential. These have
not only lessened the insect occurrence but also provided supportable outcomes
for increasing the plant defenses (Boer
et al. 2019; Li et al. 2020;
Rizzo et al. 2020).
In case of induced-resistance, foliar application of salicylic/citric
acid and related compounds have been shown to invigorate the built-in plant
defenses against invaders, called induced systemic resistance (Züst and Agrawal
2016; Nam et al. 2020; Serteyn et al. 2020). Previously only
bio-activators/phytohormones (Benzo-thiadiazole and Jasmonic acid) have been
employed to reduce pest abundance (Selig
et al. 2016; Nouri-Ganbalani et al.
2018). But they are costly enough to restrict their field application
practically (Dhandhukia and Thakkar 2007). Also, they may antagonize plant defense against the specialist pest due to
issues in defensive signaling crosstalk (Schmiesing et al. 2016; Li et al. 2019;
Irigoyen et al. 2020; Ma et al. 2020). As B. brassicae is also a specialist pest (Nouri-Ganbalani et al. 2018), thus some alternative
bio-activators such as SA and CA suitable against such pest, are needed to
explore.
Our work has suggested the pivotal associations of using such
alternative cost-efficient and defense-effective inducers that can inflict
injuries to pest and their progenies. We used salicylic and citric acids, with
different levels of foliar concentrations, to induce resistance against B. brassicae. Important outcomes were
found, showing that SA and CA were not only helpful for reducing B. brassicae development period and
reproduction times but also its progenies and nymph percent survival was
reduced significantly. Insect developmental and reproduction time may be
retarded due to the effect of defense genes (PR and PIN) and metabolites that are shown to be elicited
in plants by IR treatments (Studham and MacIntosh 2013; Ma et al. 2020; Irigoyen et al.
2020). These metabolites are usually
glucosinolates, phenolics, and some other flavonoids (Studham and MacIntosh
2013; Khoshfarman-Borji et al. 2020).
B. brassicae was also able to
produce the least number of next-generation progenies and IBA with lesser
percent survival compared to control plants. This was happened since B. brassicae reproduction time was
shortened, thus lesser numbers of nymphs/female were produced in a successive
generation. Additively, less number of immature became adults with the least
percent survival. The similar responses have
been portrayed by Nouri-Ganbalani et al.
(2018) and Khoshfarman-Borji et al.
(2020),who have described that aphid offspring become less viable after
feeding on plants under IR treatments (Khoshfarman-Borji
et al. 2020) showed the
effectiveness of SA and humic acid induced-resistance implicating different
biological fitness attributes of B.
brassicae aphids on B. napus with
similar results.
Work on other plants like wheat, barley, soybean, and Brassica spp., has shown the effectiveness of
induced-resistance against bio-fitness attributes of Myzus persicae and Lipaphis
spp. aphids (Chaman et al. 2003; Studham and MacIntosh
2013; Mahmoud and Osman 2015; Sun et al.
2016; Nouri-Ganbalani et al. 2018).
Its underlying mechanism involves the activation of defense transcriptional
machinery, against aphid infestations (Studham and MacIntosh 2013).
Associatively, to reference further, decrements in these biological parameters,
have also been attributed to diverse packaging of secondary range biochemicals that can restrict phloem uptake
and nutrient digestion in aphids (Chaman
et al. 2003; Studham and MacIntosh 2013; Khoshfarman-Borji
et al. (2020).
Silicon and ammonium sulphate, although not appeared much in pest
reduction studies, however, their efficiencies to activate plant built-in
defense machinery, are giving insights to use them as pest control implements
(Teixeira et al. 2017; Boer et al. 2019). Henceforth, as per
assumption, soil routed Si and AS showed better results to affect B. brassicae developmental and
reproductive performances in dose-dependent manner (Fig. 2a–e). In the ND
category, compared to AS, Si has been recorded to delay insect development both
in 25 and 50 kg ha-1 doses, but it was evident that doubling the
dose (50 kg ha-1) is not retarding the pest developmental time twice
as expected. The response may be occurred due to excessive Si fertilization
that renders the plant inefficient to optimize its defense system further (Rowe et al. 2020; Amsterdam 2020). B. brassicae reproduction time, progeny,
and adults appearing from these progenies (IBA) along with their percent
survival were also affected significantly. Delay in development and reduction
in reproducing days to give next progenies are responsible for lesser nymphs to
become adults with the least viable generation. Such implications of Si for
aphid have been considered to be associated with reduced food intake in
offspring as Si cements the plant tissues against mechanical injuries
(Alhousari and Greger 2018).
Besides, least nutrient digestibility indices with severe impact on
aphid growth and biological performances have also been mentioned (Alhousari
and Greger 2018). Boer et al. (2019)
have exhibited Si effectiveness to retard nutrient digestibility in sap-sucking
and leaf chewing insect pests due to coagulation and fabrication of food
materials. Moise et al. (2019) mentioned the involvement of plant nutrient
status and insect physiology to impede insect growth and digestion indices
under Si application.
Likewise, mentioned biological fitness parameters were also impaired in
AS application. However, AS in 25 kg ha-1 was working more
competently, contrasting to 50 kg-1. Similar dose responses were
shown for progeny production, IBA, and nymph survival. The efficient
performance of AS 25 kg may be associated with higher production of defense
compounds due to active presence of sulphur ingredient. Sulphur is thought to
work and generate efficient sources of glucosinolates to deter the aphids on
brassica crops (Badenes-Pérez et al.
2020; Santos et al. 2018). Also,
Agathokleous et al. (2019) have
revealed the bio-inhibitory impacts of AS for insects on brassica plants even
under ozone pollution. But this effect may be altered under excessive or high
AS doses, especially for insect defense (Sabino et al. 2018).
Furthermore, both soil dose responses at 25 kg and 50 kg were
comparatively more efficient against control treatment plants. But reduced responses
of higher AS dose (50 kg), was attributive of increased plant nitrogen content.
Such higher nitrogen contents can favour the insect pest (Santos et al. 2018; Agathokleous et al.
2019). This value-added improvement in plant nitrogen levels has been revealed
by Syeed et al. (2011) due to
increments in plant root areas that were noticed under higher nitrogen
fertilizer doses. Thus, the inefficiency of 50 kg AS over to 25 kg, as
suggested from enhanced feeding and reproduction of B. brassicae on AS treated plants was connected with higher plant
nitrogen contents.
Sulphur-integration with compost in elemental and bio-sulphur
formulations against B. napus aphid
was assessed due to the role of sulphur in the production of different
anti-insect defense complexes (phenolics, flavonoids, and glucosinolates) in
brassica plants (Santos et al. 2018;
Badenes-Pérez et al. 2020). In the
present study, sulphur results were more operative and augmentative for
bio-formulations to restrict aphid biological parameters. Moreover, in
comparison to elemental sulphur, bio-sulphur was performing better with compost
combinations. Insect developmental period, reproduction, and progeny
production, along with IBA and nymph survival and mortalities, were all
forceful to generate resistance responses in sulphur bio-formulation (BS).
BS has performed proficiently to impede B. brassicae bio-fitness compared to elemental formulations. This
activity of BS has been produced under microbial decomposition, which, in turn,
has exhibited to make the sulphur available efficiently to plants (Kumar et al. 2018; Singh et al. 2020). Moreover, the presence of beneficial microbial fauna
in BS may have increased the plant capabilities to detoxify redox species under
stress responses. Besides these, plant physiology and volatile organic
compounds were also recorded to improve by microbial activities, thus, to reinforce plant defense (Raza and Shen 2020).
Furthermore, higher contents of sulphur (90 ± 1.5%) in elemental formulation-ES
compared to BS (70% sulphur), may also render ES treatment less valid. Higher
sulphur doses may also sometime show implications to plant growth and defense
mechanism. Also, non-availability of microbial fauna may serve as another
reason to supply sulphur inefficiently to plants (Singh et al. 2020).
Concisely, the sulphur treatments, both alone and integrated, were
efficient. However, compost worked negatively to mitigate the pest. Most of the
time, positive relations to improve B.
brassicae reproduction and development were recorded for compost, compared
to the control plants. The responses may occur because of the presence of high
proportions of nitrogen (17.1 g kg-1) in compost to favor the aphid.
Nonetheless, higher B. brassicae
mortalities compared to the control plants were also there. But this may be
attributive of the presence of phosphorous (3.01 g kg-1) in compost.
Phosphorous has been documented to work negatively against the biological
fitness characteristics of different insect pests (Cease et al. 2016). Other reinforcing arguments were manifested by the
fact that sulphur has more roles in the production of anti-aphid glucosinolates
(Rehman et al. 2013). Additively,
increased uptake of essential nutrients (Chaman et al. 2003; Sun et al.
2016; Syeed et al. 2011), is also
mentioned under sulphur application to enhance plant resistance against the
pest.
The
present studies have given a clear view for inducer mediated resistance under
different inducer categories to be functionally operative to reduce the biological
fitness of B. brassicae. All crucial
parameters like developmental period, reproduction times, progeny production,
immature becoming adults, and percent survival was decreased significantly.
However, the type and concentration of inducers were of real concern.
Additionally, increasing the concentration of inducers may be effective against
insect pests, but phytotoxicity must be considered in all orientations.
Molecular/genetics-based research is also being suggested to explore the
underlying mechanism of such resistance responses. Moreover, field-level
applications and evaluations are also being recommended for further
investigations.
Acknowledgment
We
acknowledge the role of ORIC (UAF), and HEC to facilitate the research.
Author Contributions
Muhammad Wajid Javed, Mansoor ul Hasan, Muhammad
Sagheer and Shahbaz Talib Sahi planned the experiments. Mansoor ul Hasan and
Muhammad Sagheer designed the experiment. Muhammad Wajid Javed conducted the
experiments, and Mansoor ul Hasan and Shahbaz Talib Sahi performed statistical
analysis. Muhammad Wajid Javed and Mansoor ul Hasan wrote the manuscript.
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