Solatenol - the second generation benzonorbornene SDHI carboxamide with outstanding performance against key crop diseases

Abstract

Solatenol (common name benzovindiflupyr) is a new broad spectrum foliar fungicide discovered and developed by Syngenta. It is the third Syngenta succinate dehydrogenase inhibitor (SDHI), and the second in the benzonorbornene amide subclass. The focus of the Solatenol project was on finding compounds with high intrinsic activity against soybean and cereal diseases, in particular Asian Soybean Rust (Phakopsora pachyrhizi) and Septoria leaf blotch (Zymoseptoria tritici). Solatenol is highly active on other major pathogens, e.g. Rhizoctonia spp. and Botrytis cinerea. The very high affinity to succinate dehydrogenase results in its high intrinsic activity. This, together with strong binding to the plant's wax layer, provides long lasting disease control. Solatenol is safe to the crop, also when applied in mixture with DMI and QoI compounds.

Full text

1
Solatenol - The Second Generation
Benzonorbornene SDHI Carboxamide with
Outstanding Performance against Key Crop
Diseases
Guicherit E., Bartlett D, Dale SM, Haas H-U., Scalliet G, Walter H.
Syngenta Crop Protection AG, Schwarzwaldallee 215, CH-4002, Basel, Switzerland;
Email: eric.guicherit@syngenta.com
ABSTRACT
Solatenol (common name benzovindiflupyr) is a new broad spectrum foliar fungicide
discovered and developed by Syngenta. It is the third Syngenta succinate dehydrogenase
inhibitor (SDHI), and the second in the benzonorbornene amide subclass. The focus of the
Solatenol project was on finding compounds with high intrinsic activity against soybean and
cereal diseases, in particular Asian Soybean Rust (Phakopsora pachyrhizi) and Septoria leaf
blotch (Zymoseptoria tritici). Solatenol is highly active on other major pathogens, e.g.
Rhizoctonia spp and Botrytis cinerea. The very high affinity to succinate dehydrogenase
results in its high intrinsic activity. This, together with strong binding to the plant’s wax
layer, provides long lasting disease control. Solatenol is safe to the crop, also when applied
in mixture with DMI and QoI compounds.
INTRODUCTION
Researchers within Syngenta started working in the SDHI area in 1999. The first
breakthrough in this area was the discovery of the benzonorbornene amide class, which
revealed a large number of good chemical leads with the potential to cover the foliar cereals
segment. Isopyrazam was the result of a first optimization of this class and was introduced to
the market in 2010, mainly tailored for foliar use in the cereals segment (Harp et al. 2013)
(Figure 1).
Figure 1. Structures of isopyrazam and Solatenol
isopyrazam
(syn/anti mixture)
Solatenol
(racemic)

2
Solatenol is the result of an optimization program mainly looking at the efficacy against
Asian Soybean Rust (ASR), caused by Phakopsora pachyrhizi. Solatenol’s structure is
closely related to isopyrazam. In addition to the outstanding efficacy against ASR, Solatenol
delivers broad spectrum fungal control including control of major diseases in the cereals
segment.
MATERIAL AND METHODS
SDH enzyme inhibition tests
SDH enzyme inhibition was tested in vitro on Zymoseptoria graminicola, Botrytis cinerea
and Rhizoctonia solani using purified mitochondrial suspensions. Mitochondrial
purifications and test conditions were performed following already described procedures
(Scalliet et al. 2012). These assays enable comparison of the intrinsic potency displayed by
carboxamides of different structures at the level of the SDH enzyme. The inhibition of
ubiquinone reduction was monitored in the presence of succinate and of a terminal electron
acceptor (DCPIP) whose reduction was monitored spectrophotometrically at 595 nm. The
slopes of DCPIP reduction were used for calculation of the half inhibitory concentrations
(IC50) as described in Zeun et al. (2013).
Biological Activity on Asian Soybean Rust (ASR)
SDH enzyme inhibition was determined in situ using a whole plant-leaf disk assay. The
shoot of 24-days old soybean plants was removed just after the first trifoliate leaf one day
before application. The plants were sprayed with the test compounds at equivalent of 50 l/ha
spray volume. The compounds were sprayed at 12 rates, adapted to the known potency of the
compounds on ASR (Table 1). One day after application, 6 leaf discs per treatment were
taken from the first trifoliate leaf and placed into 24-multiwell plates. The leaf discs were
inoculated with rust spores one day after application. After dark incubation for 48 h, the
plates were further incubated under light at 22°C for another 10 days. As a reference, 6 leaf
discs of untreated plants were placed on each of the plates. Disease severity was determined
visually and activity calculated in comparison to the infestation on leaf discs of the untreated
check.
Table 1: Compound rates applied on whole soybean plants to determine the in situ activity of 3
different SDHI against soybean rust
g/ha in 50 l/ha spray volume
Solatenol
30.0
19.8
13.1
9.8
7.4
5.5
4.1
3.1
2.3
1.5
1.0
0.7
fluxapyroxad
50.0
33.0
21.8
16.3
12.3
9.2
6.9
5.2
3.9
2.6
1.7
1.1
penthiopyrad
100.0
66.0
43.6
32.7
24.5
18.4
13.8
10.3
7.8
5.1
3.4
2.2

3
Biokinetics
Corn
Corn plants cv. Avenir were grown under glasshouse conditions to the 6-7 leaf stage and
sprayed with Solatenol 100g/l EC or 100g/l EC + 0.3% v/v NIS adjuvant in a tracksprayer at
a rate of 30g ai/ha in a spray volume of 150l/ha. Immediately after spraying, the youngest
fully expanded leaves from ten replicate plants were removed and the Solatenol retained on
the foliar surface removed to allow quantification of foliar spray retention. Six hours and 1,
3 and 7 days after spraying, unabsorbed Solatenol was recovered and quantified from leaf
surfaces, epicuticular waxes and plant tissue.
RESULTS AND DISCUSSION
SDH enzyme inhibition tests
The results show that Solatenol is a highly potent SDH inhibitor on a range of pathogens
(Figure 2). In many cases the intrinsic activity of Solatenol was superior to other SDHI’s.
Bioavailability; a major factor influencing biological efficacy, may explain some
discrepancies when in vitro results for SDH inhibition are compared to in vivo activity within
pathogens. The outstanding performance of Solatenol on rusts, and in particular on soybean
rust (Figure 7), is most likely the result of a combination of its superior potency on the
targeted SDH rust enzyme, and a good fit of physico-chemical properties and bioavailability
required for optimal activity.
Figure 2: In vitro inhibition of the succinate ubiquinone oxidoreductase activity by
carboxamide inhibitors. IC50 values are the concentrations required for each
inhibitor to half-inhibit DCPIP reduction on M.graminicola, B.cinerea and
R.solani mitochondrial suspensions. Presented values are based on triplicate
determinations ±SD.
Biological Activity on soybean rust, Phakopsora pachyrhizi
10 days after inoculation the disease severity on untreated, infected checks was up to 85 %;
on average 80 %. Infestation on treated leaves ranged depending on rate from 0 to 80 %.
Rate for rate, Solatenol showed best activity on soybean rust, clearly more active when
compared to fluxapyroxad and penthiopyrad. (Figure 3)

4
Figure 3: Leaf discs in multiwell plates of comparable treatments, 5.5g/ha for Solatenol, 5.2 g
/ha for fluxapyroxad and 5.1 g/ha for penthiopyrad, showing infestation levels of
the leaf discs with Phakopsora pachyrhizi.
Data was analyzed statistically and did not benefit from transformation. Dose-response
relationships (Figure 4) were calculated using the Log-logistic model with lower (0) and
upper (100) asymptotes constrained, by calculating the data in MS Excel using the
Bioassay97 MS-Excel macro (Onofri 2005).
Figure 4: Dose response relationships of 3 different SDHI on Phakopsora pachyrhizi on
soybean leaves, based on 12 different rates adapted to each of the compounds.
The dose response curves differed, showing different dose dependent activity of each of the
compounds on soybean rust. Solatenol was more active compared to fluxapyroxad and
penthiopyrad. Based on the dose-response relationships effective concentrations at distinct
control levels could be derived (Table 2). Since the fitted dose-response curves were not
parallel, relative potencies of the compounds varied, dependent on the different control
levels. However a clear result would be that one would need at least 3 times more ai. of
either fluxapyroxad or penthiopyrad compared to Solatenol to get comparable control of
soybean rust (Table 2).
Table 2: Dose estimates (g/ha) of SDHI compounds against soybean rust for response at
distinct percent control scale
Solatenol
fluxapyroxad
penthiopyrad
50 % control
4.0
13.4
16.6
70 % control
6.2
19.4
21.3
90 % control
12.1
35.1
31.4
Solatenol, 5.5g /ha fluxapyroxad, 5.2g /ha penthiopyrad, 5.1g /ha

5
Biokinetics
Corn
The distribution over time of Solatenol between the foliar surface, epicuticular wax and
within the leaf tissue was significantly influenced by the presence of adjuvant, with adjuvant
significantly decreasing recoveries from within the wax layer and increasing in the foliar
tissue itself as shown in Figure 5. When Solatenol EC was applied alone, the wax layer
acted as a major reservoir for the absorbed compound with approximately 63% (4.03
ug/gFW) of recovered Solatenol being quantified in the wax when sampled 3 days after
application. In contrast, the addition of adjuvant decreased the wax residence time such that
only 31% (2.02 ug/gFW) remained in the wax layer with a consequent increase in Solatenol
in the leaf tissue to 53% (3.44 ug/gFW) from the 7% (0.43 ug/gFW) recovered without
adjuvant (Figure 5).
Figure 5: Distribution over time of Solatenol between the foliar surface, epicuticular wax and
within the leaf tissue of corn
Wheat
In numerous field trials Solatenol applied at 75g/ha in mixture with a triazole for resistance
management has shown excellent efficacy on Zymoseptoria tritici which positively reflects
on yield (Figure 6). The trials also showed Solatenol’s excellent crop tolerance, being safe to
wheat.
Figure 6: Control of Zymoseptoria tritici in wheat.

6
Figure 7: Control of Phakopsora pachyrhizi in soybean.
CONCLUSIONS
Solatenol is Syngenta’s second generation benzonorbornene amide fungicide belonging to
the group of succinate dehydrogenese inhibitors (SDHI) with high intrinsic activity on a
broad range of plant fungal diseases. Solatenol binds strongly to the plant’s wax layer where
it forms a reservoir from which it slowly translocates into the tissue. Movement with the
sapstream is very limited. Adding an NIS adjuvant, either built-in or in tank mix, greatly
enhances uptake which can positively reflect on efficacy, spectrum and duration of control.
Solatenol is highly active on key pathogens at rates between 30 to 75g/ha when applied
preventative or early curative. The performance on Asian soybean Rust sets new standards.
In wheat Solatenol mixed with a triazole provides Zymoseptoria tritici control similar to the
best commercial standard.
REFERENCES
Zeun R; Scalliet G; Oostendorp M (2013). Biological activity of sedaxane a novel broad-
spectrum fungicide for seed treatment. Pest Management Science, 69 (4), 527-34.
FRAC Code List ©*2013: Fungicides sorted by mode of action (including FRAC Code
numbering). www.frac.info (date of access 01.08.2013).
Scalliet G; Bowler J; Torsten, L; Kirchhofer A; Steinhauer D; Ward K; Niklaus M; Verras A;
Csukai M; Daina A; Fonné-Pfister R (2012). Mutagenesis and Functional Studies
with Succinate Dehydrogenase Inhibitors in the Wheat Pathogen Mycosphaerella
graminicola. PLOS ONE.
www.plosone.org/article/info:doi/10.1371/journal.pone.0035429 (date of access
01.08.2013).
Harp, T. L.; Godwin JR; Scalliet G; Walter H; Stalker AD.; Bartlett DW.; Ranner DJ (2011).
Isopyrazam, a new generation cereal fungicide. Aspects of Applied Biology 106,
113-120.
Sezione Scientifica Onofri A (2005). Rivista Italiana di Agrometeorologia. (3), 40-45.