Journal of Pesticide Science最新文献

In recent years, the stable supply of natural rubber has been threatened by a new leaf fall disease (LFD) caused by filamentous fungi. We screened pesticides to control the growth of Neopestalotiopsis sp. and Colletotrichum sp., which are considered to be the causal agents of LFD in rubber trees. We identified two effective pesticides, Quinondo 80% WP and Topsin M WP. When these two candidate pesticides were used in combination at 10 ppm each, there was enhanced inhibition of growth of both fungal species. Furthermore, the use of Quinondo 80% WP was shown to suppress the development of necrotic lesions caused by Neopestalotiopsis in rubber seedlings. These results suggest that Quinondo 80% WP is effective in controlling the spread of damage caused by LFD infection in rubber trees, and further verification of the concentration and method of application is needed to further demonstrate its effectiveness.

We investigated whether various modified cyclodextrins (CDs) and emulsifiers could be applied as dispersing agents in ready biodegradability tests of poorly water-soluble substances. Trimethylated α-, β-, and γ-CDs and partially methylated β-CD were not biodegraded in the test period but accelerated the biodegradation of octabenzone and anthraquinone. The process by which trimethylated α-, β-, and γ-CDs enhance the biodegradation of test substances has been partially uncovered. These CDs create inclusion complexes with the substances, which then coalesce into larger aggregates. These aggregates disperse throughout the testing medium and attach to clusters of activated sludge, known as flocs. This close contact with the sludge speeds up the breakdown of the hydrophobic substances being tested.

Root parasitic broomrape (Phelipanche and Orobanche spp.) weeds cause devastating damage to agricultural production all around the world. The seeds of broomrapes germinate when they are exposed to germination stimulants, mainly strigolactones (SLs), released from the roots of any plant species; however, broomrapes parasitize only dicot plants. Therefore, monocots can be trap crops for broomrapes, as they induce seed germination but are not parasitized. In this study, we examined two European and one Japanese barley cultivar for their potential as trap crops for broomrapes. We found that the European cultivars, Sebastian and Golden Promise, are good potential trap crops, as they produce more SLs and exhibit higher mycorrhizal colonization rates as compared to the Japanese cultivar Shunrai.

A search for antifungal compounds from the mushroom Coprinus comatus using a bioassay-guided chromatographic fractionation approach led to the discovery of a novel polyketide harboring a rare 3,3a,9,9a-tetrahydro-1H-furo[3,4-b]chromen-1-one skeleton. The novel compound was named coprinolide. The inhibitory activity and fungicidal potential of coprinolide were evaluated against five economically important plant-pathogenic fungi. Coprinolide showed inhibitory effects on conidial germination and germ tube elongation of all tested fungi. The strongest effect was observed for Colletotrichum orbiculare with half-maximal inhibitory concentrations of 7.1 ppm and 8.2 ppm for conidial germination and germ tube elongation, respectively. Furthermore, coprinolide exhibited fungicidal activity against the tested fungi by inhibiting conidial germination to conidial death as confirmed by fluorescence microscopy using fluorescein diacetate and propidium iodide. These findings showed the potential of the mushroom as a source of a novel bioactive compound with promising agricultural application as an antifungal agent against different plant-pathogenic fungi.

When a test substance is poorly water-soluble, it can be adsorbed onto silica gel to facilitate dispersibility in a ready biodegradability test. To uniformly adsorb the test substance onto silica gel, the substance is dissolved in a solvent and then mixed with the silica gel. It is desirable for the solvent to completely evaporate afterward. In this study, we identified n-hexane as a suitable solvent for this purpose. Furthermore, through fluorescence observation, we revealed that the test substance adsorbed onto the silica gel adhered to activated sludge flocs. This is thought to improve contact between the test substance and microorganisms, thereby accelerating biodegradation.

Agonists of insect hormones, namely molting hormone (MH) and juvenile hormone (JH), disrupt the normal growth of insects and can be employed as insecticides that are harmless to vertebrates. In this study, a series of experiments and computational analyses were conducted to rationally design novel insect hormone agonists. Syntheses and quantitative structure-activity relationship (QSAR) analyses of two MH agonist chemotypes, imidazothiadiazoles and tetrahydroquinolines, revealed that the structural factors important for the ligand-receptor interactions are significantly different between these chemotypes. On the other hand, a virtual screening cascade combining ligand- and structure-based methods identified a piperazine derivative as a novel JH agonist. The results obtained in this study will be useful for the future development of novel insect growth regulators.

Pyriofenone demonstrates outstanding efficacy in controlling powdery mildew. We investigated the impact of pyriofenone on the infection processes and cytological features of Blumeria graminis f. sp. tritici on wheat leaves. The preventive application of pyriofenone before inoculation did not inhibit conidial germination but effectively suppressed both appressorial and haustorial formation. Notably, haustorial formation was effectively inhibited, resulting in the complete suppression of successive lesion development and sporulation. Curative application of pyriofenone after inoculation also inhibited lesion expansion and sporulation. Furthermore, it had considerable impact on the morphogenesis of powdery mildew fungus. We observed multi-formed secondary appressoria, shrunken or bifurcated hyphae, abnormal conidiophores, and clubbed conidia-like structures. Subsequently, we employed a histochemical approach to analyze the localization of essential components for the polar growth of fungal hyphae. Pyriofenone induced mislocalization of the actin cytoskeleton, β-glucan and cytoplasmic vesicles, although it did not affect tubulin orientation.

An antifungal polyene-decalin polyketide natural product, burnettiene A (1) has been re-discovered from the culture broth of Lecanicillium primulinum (current name: Flavocillium primulinum) FKI-6715 strain utilizing our original multidrug-sensitive yeast system. This polyene-decalin polyketide natural product was originally isolated from Aspergillus burnettii. The antifungal activity of 1 against Candida albicans has been reported. However, only one fungal species for the antifungal activity of 1 has been revealed, and details of the antifungal activity against other pathogenic fungus remain unknown. After extensive screening for antifungal activity, we found that 1 exhibits broad antifungal activity against pathogenic plant fungi, including Colletotrichum gloeosporioides, Botrytis cinerea, Pyricularia oryzae, Leptosphaeria maculans, and Rhizoctonia solani. Furthermore, we synthesized 12 derivatives from 1 and evaluated their antifungal activity to reveal the detailed structure-activity relationship. The methyl ester derivative showed antifungal activity against Saccharomyces cerevisiae 12geneΔ0HSR-iERG6 100-fold more potent than that of 1. Our research indicates that 1 would be a promising natural product as a new fungicidal candidate and the methyl ester derivative especially has great potential.

Strigolactones (SLs) are a class of plant hormones that play several roles in plants, such as suppressing shoot branching and promoting arbuscular mycorrhizal symbiosis. The positive regulation of plant disease resistance by SLs has recently been demonstrated by analyses using SL-related mutants. In Arabidopsis, SL-mediated signaling has been reported to modulate salicylic acid-mediated disease resistance, in which the priming of plant immunity plays an important role. In this study, we analyzed the effect of the synthetic SL analogue rac-GR24 on resistance against necrotrophic pathogen Botrytis cinerea. In rac-GR24-treated plants, disease resistance against B. cinerea was enhanced in an ethylene- and camalexin-dependent manners. Expression of the ethylene-related genes and the camalexin biosynthetic gene and camalexin accumulation after pathogen infection were enhanced by immune priming in rac-GR24-treated plants. These suggest that SL-mediated immune priming is effective for many types of resistance mechanisms in plant self-defense systems.

The objective of the present study is to provide reliable concentration values as assigned values for target pesticides in brown rice samples used in proficiency testing (PT) organized by the Hatano Research Institute (HRI). The test samples for PT were prepared by immersing brown rice in the pesticide solution and using a spray dryer by the HRI. Homogeneity and stability assessments were performed for PT samples, and the relative uncertainties due to inhomogeneity and instability were 0.58 %–0.78 % and 0 %–0.96 %, respectively. Quantification for the assigned values of target pesticides by the National Metrology Institute of Japan (NMIJ) was carried out using the multiple analytical methods including Japanese official analytical method, QuEChERS, and modified QuEChERS, which were combined with isotope dilution mass spectrometry, to ensure the reliability of the analytical results. The NMIJ assigned values were 0.065±0.004 mg/kg for chlorpyrifos, 0.217±0.012 mg/kg for diazinon, 0.138±0.008 mg/kg for fenitrothion, and 0.138±0.008 mg/kg for malathion.