Tomato leaf mold caused by Passalora fulva is a significant disease in tomato production. We isolated several types of boscalid-resistant isolates in the Gifu and Mie Prefectures of Japan. Sequencing analysis of succinate dehydrogenase (Sdh) subunits B, C, and D genes strongly indicated that four amino acid substitutions—T78I, N85K, N85S, and H151R in SdhC—conferred boscalid resistance. We conducted SNP assays to detect each mutation using qPCR techniques and revealed that all 35 resistant isolates had one of these mutations in the SdhC. Among the four resistance types, N85K isolates exhibited the highest, N85S isolates showed the lowest, and T78I and H151R isolates displayed moderate resistance to boscalid. These mutations also conferred cross-resistance to other succinate dehydrogenase inhibitor (SDHI) fungicides, including penthiopyrad, pyraziflumid, fluopyram, and isofetamid. A predicted SdhC protein structure, created by I-TASSER, suggests that the amino acid at position 151 is located close to those of positions 78 and 85, likely forming the SDHI-binding pocket of the protein.

This study focused on the chemical synthesis of auxin analogs, wherein a trifluoromethyl group was introduced near the carboxyl group in the side chain of natural and synthetic auxins, including IAA, NAA, IBA, 2,4-D, and 4-Cl-IAA. The effects of these synthetic compounds and natural auxins on plant growth regulation and callus growth were evaluated. In experiments with black gram, CF₃-IAA and 4-Cl-CF₃-IAA exhibited comparable effects to the parent compound, IAA. Meanwhile, CF₃-NAA, CF₃-2,4-D, CF₃-IBA-1, and CF₃-IBA-2 displayed effects that differed considerably from those of their respective parent auxins. In experiments with lettuce, CF₃-IAA, 4-Cl-CF₃-IAA, CF₃-NAA, CF₃-2,4-D, and CF₃-IBA-1 showed effects comparable to the corresponding parent auxins. However, at low concentrations, these analogs induced hypocotyl and root elongations, a response distinct from that observed with their parent compounds. Furthermore, CF₃-IBA-2 considerably promoted hypocotyl and root elongations across all concentrations relative to the control. The addition of synthetic compounds to callus cultures revealed that CF₃-IAA, 4-Cl-CF₃-IAA, CF₃-NAA, and CF₃-2,4-D promoted callus proliferation, whereas CF₃-IBA-1 and CF₃-IBA-2 did not enhance callus growth.

Capsaicin inhibits the current flow in the voltage-gated sodium channels (VGSCs) of mammals and insects. The aim of the present study was to elucidate capsaicin toxicity in pyrethroid-susceptible and knockdown resistant (kdr; with reduced pyrethroid sensitivity) strains of the German cockroach (Blattella germanica) and its effects on VGSCs carrying the kdr mutation. Injection tests revealed that adult cockroaches from susceptible and kdr strains exhibited sluggish movement and paralysis upon abdominal capsaicin administration, consistent with its inhibitory effect on VGSC currents. The LD₅₀ values of capsaicin were 16 and 36 µg per insect for the susceptible and kdr strains, respectively, yielding a resistance ratio of 2.3. Two-electrode voltage clamp assays showed that the EC₅₀ values for the capsaicin-mediated inhibition of VGSC currents were 4.27 and 9.19 µM for susceptible and kdr mutant channels, respectively, yielding a resistance ratio of 2.2. The findings indicate that capsaicin retains inhibitory activity against insect VGSCs even in the presence of kdr mutations.

N-(3-Phenylisoxazol-5-yl)benzamides (5-benzoylamino-3-phenylisoxazoles: IOXs) with various substituents at two benzene rings were synthesized, and the chitin synthesis inhibition was measured in the cultured integumentary system of Chilo suppressalis. Larvicidal effects against C. suppressalis and Spodoptera litura were also examined, and the larvicidal activity in terms of the 50% lethal dose (LD₅₀) was determined for some compounds. Among IOXs with various substituents at the benzoyl moiety, 2,6-difluoro-substituted (2,6-F₂) benzoyl analogs showed the highest chitin synthesis activity. The larvicidal activities against C. suppressalis and S. litura were 1/138 and 1/35 that of diflubenzuron, a representative benzoylphenylurea-type insecticide, respectively. In a further study, 2,6-F₂ benzoyl analogs with various substituents at the phenyl moiety, such as Br, CF₃, CN, OEt, Ph, and alkyls (CH₃, Et, i-Pr, n-Bu, and t-Bu), were synthesized, and their chitin synthesis inhibition in the Chilo integument and their larvicidal activity against S. litura were quantitatively measured. The introduction of bulky CF₃ and t-Bu at the phenyl moiety of 2,6-F₂ benzoyl analog favorably enhanced the larvicidal activity against S. litura.

Developing new agrochemicals is essential for sustainable agriculture and global food security. Our group focused on natural products that control plant pathogens, conducting synthetic research across three key areas of interest: antimicrobial compounds, phytoalexins, and microbial signaling molecules. We established new methods for producing chiral allylic alcohols as useful synthetic intermediates for natural product synthesis via the enantioselective synthesis of antimicrobial agents such as peniciaculins. In the phytoalexin research, the synthesis of biosynthetic intermediates enabled the elucidation of enzyme functions in terms of their biosynthesis and the confirmation of absolute configurations, deepening our understanding of plant defense systems. Furthermore, the total synthesis and biosynthetic studies of Phytophthora mating hormones revealed a unique chemical relay system regulating sexual reproduction. These findings emphasize the importance of synthetic chemistry in advancing natural product research and offer new strategies for crop protection. Our interdisciplinary approach paves the way for future innovations in combating agricultural pests and diseases.

Oxazosulfyl, a novel insecticide originally discovered and developed by Sumitomo Chemical Co., Ltd., belongs to a new chemical class, the sulfyl group, structurally characterized by its ethylsulfonyl moiety. It exhibits excellent control against a broad range of major rice insect pests, including Coleoptera, Hemiptera, Lepidoptera, and Orthoptera, through nursery-box application. With a novel structural backbone and mode of action, this insecticide is classified by the Insecticide Resistance Action Committee as the sole member of novel code 37, vesicular acetylcholine transporter inhibitor. A substantial number of field studies in rice paddy fields have demonstrated that oxazosulfyl, registered in Japan in April 2021 as ALLES^® granules, is highly effective against populations that have developed reduced sensitivity or resistance to existing insecticides. Given these favorable properties, oxazosulfyl is expected to contribute to the management of insecticide resistance, the reduction of agricultural chemical use, labor savings, and sustainable agriculture as a next-generation insecticide.

Acynonapyr is a novel acaricide developed by Nippon Soda Co., Ltd. It contains a unique azabicyclic ring and oxyamine structure and represents the first agricultural chemical that targets calcium-activated potassium channels, classified as Group 33 in the IRAC Mode of Action Classification. Acynonapyr exhibits high selectivity against spider mites across all developmental stages and has minimal impact on beneficial insects and natural enemies, rendering it suitable for Integrated Pest Management systems. The compound acts by inhibiting potassium ion flow through K_Ca2 channels in spider mites, leading to neurological symptoms such as convulsions and impaired mobility and ultimately resulting in mortality. Electrophysiological studies have demonstrated that acynonapyr effectively blocks Tetranychus urticae calcium-activated potassium channels. Importantly, acynonapyr shows little activity against mammalian calcium-activated potassium channels, contributing to its favorable safety profile. The compound shows efficacy against acaricide-resistant spider mite populations, providing a useful tool for pesticide resistance management.