Long‐lasting β‐aminobutyric acid‐induced resistance protects tomato fruit against Botrytis cinerea

Minimizing losses to pests and diseases is essential for producing sufficient food to feed the world's rapidly growing population. The necrotrophic fungus Botrytis cinerea triggers devastating pre‐ and post‐harvest yield losses in tomato (Solanum lycopersicum). Current control methods are based on the pre‐harvest use of fungicides, which are limited by strict legislation. This investigation tested whether induction of resistance by β‐aminobutyric acid (BABA) at different developmental stages provides an alternative strategy to protect post‐harvest tomato fruit against B. cinerea. Soil‐drenching plants with BABA once fruit had already formed had no impact on tomato susceptibility to B. cinerea. However, BABA application to seedlings significantly reduced post‐harvest infection of fruit. This resistance response was not associated with a yield reduction; however, there was a delay in fruit ripening. Untargeted metabolomics revealed differences between fruit from water‐ and BABA‐treated plants, demonstrating that BABA triggered a defence‐associated metabolomics profile that was long lasting. Targeted analysis of defence hormones suggested a role of abscisic acid (ABA) in the resistance phenotype. Post‐harvest application of ABA to the fruit of water‐treated plants induced susceptibility to B. cinerea. This phenotype was absent from the ABA‐exposed fruit of BABA‐treated plants, suggesting a complex role of ABA in BABA‐induced resistance. A final targeted metabolomic analysis detected trace residues of BABA accumulated in the red fruit. Overall, it was demonstrated that BABA induces post‐harvest resistance in tomato fruit against B. cinerea with no penalties in yield.     

Feeding‐deterrent activity of α‐asarone isomers against some stored Coleoptera

All isomers of α‐asarone [(E)‐4‐prop‐1‐enyl‐1,2,5‐trimethoxybenzene] were tested for their feeding deterrent activity against adults of Sitophilus granarius and Tribolium confusum and larvae of Trogoderma granarium and Tribolium confusum. (E)‐2‐prop‐1‐enyl‐1,3,5‐trimethoxybenzene exhibited the strongest deterrent activity against all the species tested. The total coefficients of deterrency for this compound were 140.6 and 169.7 for Tribolium confusum adults and larvae, respectively, and 144.9 and 104.6 for larvae of Trogoderma granarium and adults of Sitophilus granarius, respectively. © 2000 Society of Chemical Industry     

Bicyclophosphorothionate antagonists exhibiting selectivity for housefly GABA receptors

2,6,7-Trioxa-1-phosphabicyclo[2.2.2]octane 1-sulfides (bicyclophosphorothionates) with various C_1–4 alkyl groups at the 3- and 4-positions were synthesized and tested for their ability to compete with [³H]4′-ethynyl-4-n-propylbicycloorthobenzoate (EBOB), a non-competitive antagonist of γ-aminobutyric acid (GABA) receptors, for specific binding to rat-brain and housefly-head membranes, and for their insecticidal activity against houseflies. Among the 3,4-substituted analogues, 20 compounds were selectively active for housefly GABA receptors versus rat GABA receptors. The 3-alkyl groups of C₃ length and the 4-alkyl groups of C₄ length were tolerated in housefly receptors, whereas such bulky substituents were deleterious in rat receptors. The 4-isobutyl-3-isopropyl analogue was the most potent in housefly receptors (IC₅₀ = 45.2 nM ), and tert-butylbicyclophosphorothionate (TBPS), with the 4-tert-butyl group and no 3-substituent, was the most potent in rat receptors (IC₅₀ = 62.2 nM ). Their receptor selectivities (rat IC₅₀/housefly IC₅₀) were 52 and 0.038, respectively. The insecticidal activity (LD₅₀) of 20 active analogues was well correlated with their potency (IC₅₀) in inhibiting [³H]EBOB binding to housefly-head membranes (r = 0.93). The results obtained in the present study indicate that the introduction of appropriate alkyl groups into the 3- and 4-positions of bicyclophosphorothionate leads to non-competitive antagonists with increased affinity and selectivity for housefly ionotropic GABA receptors versus rat GABA_A receptors. © 1999 Society of Chemical Industry     

Callose and β‐1,3‐glucanase inhibit Phytophthora cinnamomi in a resistant avocado rootstock

Phytophthora root rot (PRR) of avocado, caused by Phytophthora cinnamomi, is a significant threat to sustainable production wherever the crop is grown. Resistant rootstocks in combination with phosphite applications are the most effective options for managing this disease. Recently, the mechanisms underpinning PRR resistance have been investigated by the avocado community. Here, biochemical assays and confocal and scanning electron microscopy were used to investigate early defence responses in PRR resistant and ‐susceptible avocado rootstocks. Zoospore germination and subsequent hyphal growth for the pathogen were significantly inhibited on the surface of resistant avocado roots. When penetration occurred in the resistant R0.06 rootstock, callose was deposited in the epidermal cells, parenchyma and cortex of roots. In addition, β‐1,3‐glucanase was released early (6 h post‐inoculation, hpi) in response to the pathogen, followed by a significant increase in catalase by 24 hpi. In contrast, susceptible R0.12 roots responded only with the deposition of lignin and phenolic compounds incapable of impeding pathogen colonization. In this study, PRR resistance was attributed to a timely multilayered response to infection by P. cinnamomi.     

Three‐dimensional quantitative structure–activity relationship analysis of acyclic and cyclic chloronicotinyl insecticides

The binding activity of chloronicotinyl insecticides, including acetamiprid, nitenpyram and related compounds, to the nicotinic acetylcholine receptors (nAChR) of houseflies was measured. These compounds were defined as ‘acyclic’ compounds. Variations in the binding activity were analysed using comparative molecular field analysis (CoMFA) which is a technique for the analysis of three‐dimensional quantitative structure–activity relationships. The CoMFA results showed that steric interactions were more significant for the acyclic compounds than for imidacloprid and its derivatives (cyclic compounds). It was also shown that the acyclic compounds could bind to housefly‐nAChR in a similar manner to the cyclic compounds, and that the electrostatic natures of the acyclic amino‐ and cyclic imdazolidine‐moieties affected their binding activity. © 2000 Society of Chemical Industry     

Recovery of solubilized δ‐endotoxin from Bacillus thuringiensis subsp kurstaki fermentation broth

Insecticidal δ‐endotoxin proteins, degraded from parasporal crystals by protease, were recovered by a simple procedure using heat treatment, solubilization, and ultrafiltration of a fermentation broth of Bacillus thuringiensis subsp kurstaki HD‐1. A 68 kDa insecticidal protein was obtained and characterized by SDS‐PAGE. The procedure described gave a nearly quantitative recovery of toxicity. Furthermore, bioassay results on larvae of the diamondback moth (Plutella xylostella) showed that the 68 kDa δ‐endotoxin fraction (P1) was the principal insecticidal component to this target insect. A similar molecular mass polypeptide P2 (65 kDa) which was solubilized together with P1 from the parasporal crystals, gave relatively low mortality. © 2000 Society of Chemical Industry