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.     

Phenylalanine ammonia‐lyase and cinnamate 4‐hydroxylase genes' response to HHO in Eupatorium adenophorum

6‐Hydroxy‐5‐isopropyl‐3,8‐dimethyl‐4a,5,6,7,8,8a‐hexahydronaphthalen‐2(1H)‐one (HHO) is an allelopathic substance that is related to allelochemical metabolism in Eupatorium adenophorum. In this study, the full‐length complementary DNA of two phenylalanine ammonia‐lyase (PAL) genes and a fragment of the cinnamate 4‐hydroxylase (CA4H) gene from E. adenophorum (Ea) were cloned. The expression of all three genes was increased by the HHO treatment, with varying sensitivity: EaPAL2 > EaPAL1 > EaCA4H. Southern blotting suggested that there is a third member of the PAL gene family in this species.     

The β‐amylase genes: negative regulators of disease resistance for Verticillium dahliae

Little is known about the role of plant primary metabolism in defence against pathogens. The present study is the first investigation published that examines the role of β‐amylase (BAM) genes upon fungal, Verticillium dahliae, infection. The responses of Arabidopsis thaliana plants impaired in BAM1, BAM2, BAM3, BAM4 genes, along with double, triple and quadruple mutants of those genes, were used to explore the involvement of BAM in the host plant–V. dahliae interaction. Less severe symptoms were recorded in bam mutants compared to wild type. Real‐time quantitative PCR (qPCR) revealed that the decrease in symptom severity shown in bam plants was correlated with reductions in the growth of the pathogen in the plants. Confocal microscopy of the most and least susceptible bam mutants and the wildtype plants showed that there were no differences between them in the number of attached conidia and penetration sites on the roots. BAM1, BAM2 and BAM3 expression was altered upon V. dahliae infection in the aerial tissues of the wild type. Analysis by qPCR of the PR1 and PDF1.2 expression in the bam3, bam1234, bam14 and wildtype plants showed that PR1 was up‐regulated in the roots of bam plants upon V. dahliae infection.     

Synthesis and structure–activity relationship analysis of bicyclophosphorothionate blockers with selectivity for housefly γ‐aminobutyric acid receptor channels

BACKGROUND: Bicyclophosphorothionates (2,6,7‐trioxa‐1‐phosphabicyclo[2.2.2]octane‐1‐sulfides) are blockers (or non‐competitive antagonists) of γ‐aminobutyric acid (GABA) receptor channels. Twenty‐two bicyclophosphorothionates with different 3‐ and 4‐substituents were synthesised, and [³H]4′‐ethynyl‐4‐n‐propylbicycloorthobenzoate (EBOB) binding assays were performed to evaluate their affinities for housefly and rat GABA receptors. RESULTS: Introduction of an isopropyl group at the 3‐position enhanced the affinity of bicyclophosphorothionates for housefly GABA receptors and reduced the affinity towards rat GABA receptors. The 4‐isopentyl‐3‐isopropylbicyclophosphorothionate showed the highest affinity for housefly GABA receptors (IC₅₀ = 103 nM ) among the analogues tested, while the 4‐cyclohexylbicyclophosphorothionate showed the highest affinity for rat GABA receptors (IC₅₀ = 125 nM ). Among the bicyclophosphorothionates synthesised to date, the former analogue exhibited the highest selectivity for housefly GABA receptors, with an IC₅₀^rat/IC₅₀^fly ratio of approximately 97. Three‐dimensional GABA receptor models successfully explained the structure–activity relationships of the bicyclophosphorothionates. CONCLUSION: The results indicate that minor structural modifications of blockers can change their selectivity for insect versus mammalian GABA receptors. The substituent at the 3‐position of the bicyclophosphorothionates dictates selectivity for housefly versus rat GABA receptors. This information should prove useful for the design of safer insecticides and parasiticides. Copyright © 2010 Society of Chemical Industry     

Transfer of the β‐tubulin gene of Botrytis cinerea with resistance to carbendazim into Fusarium graminearum

BACKGROUND: Resistance to carbendazim and other benzimidazole fungicides in Botrytis cinerea (Pers. ex Fr.) and most other fungi is usually conferred by mutation(s) in a single chromosomal β‐tubulin gene, often with several allelic mutations. In Fusarium graminearum Schwade, however, carbendazim resistance is not associated with a mutation in the corresponding β‐tubulin gene. RESULTS: The β‐tubulin gene conferring carbendazim resistance in B. cinerea was cloned and connected with two homologous arms of the β‐tubulin gene of F. graminearum by using a double‐joint polymerase chain reaction (PCR). This fragment was transferred into F. graminearum via homologous double crossover at the site where the β‐tubulin gene of F. graminearum is normally located (the β‐tubulin gene of F. graminearum had been deleted). The transformants were confirmed and tested for their sensitivity to carbendazim. CONCLUSION: The β‐tubulin gene conferring carbendazim resistance in B. cinerea could not express this resistance in F. graminearum, as transformants were still very sensitive to carbendazim. Copyright © 2010 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.     

Characterization of field‐evolved resistance to Bacillus thuringiensis‐derived Cry1F δ‐endotoxin in Spodoptera frugiperda populations from Argentina

BACKGROUND

Transgenic maize (Zea mays L.) event TC1507 (Herculex^® I insect protection), expressing Cry1F δ‐endotoxin derived from Bacillus thuringiensis var. aizawai, was commercialized in 2003 in the Americas. Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) susceptibility to Cry1F was monitored annually across several regions in Argentina using diagnostic concentration bioassays. Reduced performance of TC1507 maize against S. frugiperda was reported in 2013. A resistant population was established in the laboratory and the dominance of Cry1F resistance was characterized.

RESULTS

During 2012–2015, high‐survivorship of several populations was observed in the resistance monitoring program. Reciprocal crosses of a Cry1F‐resistant population with a Cry1F‐susceptible population were evaluated to calculate effective dominance (D_ML) based on mortality levels observed at 100 µg/ml Cry1F. Two additional dominance levels (D_LC and D_EC) were calculated using lethal (LC₅₀) or effective concentration (EC₅₀) derived from concentration–response bioassays. Estimates indicated that Cry1F resistance in S. frugiperda in Argentina was either highly recessive (D_ML = 0.005) or incompletely recessive (D_LC < 0.26 and D_EC < 0.19).

CONCLUSION

This study is the first documented confirmation and characterization of S. frugiperda Cry1F field‐evolved resistance in Argentina. The resistance to Cry1F in S. frugiperda populations collected in Argentina, is autosomal and incompletely recessive similar to the resistance reported in Brazil. © 2017 The Authors. Pest Management Science published by John Wiley © Sons Ltd on behalf of Society of Chemical Industry.     

Resistance to benzimidazole can be caused by changes in β-tubulin isoforms

The summary reports work that indicates that resistance in Rhynchosporium secalis to benzimidazole fungicides could result from substitution of the normal wild-type benA β-tubulin gene by other β-tubulin isoforms. © 1999 Society of Chemical Industry