Induced Resistance Against Plasmopara helianthi in Sunflower Plants by DL-β-Amino-n-butyric acid

Sunflower plants treated with the nonprotein amitio add, DL-β-attiino- n -butyric acid (BABA) were protected against infection with Plasmopara helianthi. Soil drenches at the highest rates (150-250 mg/kg soil), applied one day before the inoculation induced high levels of protection (80-83%) against the disease and more than 90% control was observed when BABA was applied at 300 mg/kg soil. However, at this concentration phytotoxic symptoms were observed. This compound also provided a curative activity when applied one day post-inoculation. BABA had no antifungal activity in vitro against P. helianthi. The effect of BABA on zoosporangia germination was evaluated by treating pre-germinated seeds with the compound solution and the zoosporangia suspension for 3 h. Then, seeds were sown and the percentages of infected plants were determined. The other two aminobutyric acid isomers (a and g) were ineffective against downy mildew. The mechanisms by which DL-β-amino- n -butyric acid protect sunflowers against downy mildew awaits more detailed elucidation.     

Induction of Systemic Acquired Resistance in Pea against Rust (Uromyces pisi) by Exogenous Application of Biotic and Abiotic Inducers

Pea breeding for rust resistance is hampered by the little resistance available in pea. In an attempt to validate alternative control methods, we evaluated the potential of systemic acquired resistance for rust control in pea by biotic and abiotic inducers. Challenge with a virulent or with an avirulent rust isolate prior to pea rust inoculation did not induce resistance either locally or systemically. Exogenous application of salicylic acid in the range 5–10 m m prior to rust inoculation did not protect against rust locally, but reduced rust infection systemically in first upper leaf node although not in the upper ones. Some phytotoxicity was observed at 10 m m . Exogenous application of benzothiadiazole in the range 1–10 m m provided locally a 30–40% reduction in infection frequency. At least 5 m m was needed to reduce rust infection systemically in first upper leaf, and 10 m m in upper ones. Exogenous application of dl -3-amino- n -butyric acid (BABA) provided locally a 45–58% reduction in infection frequency, while systemically a 33–58 and 49–58% reduction of rust symptoms was achieved on leaves at second and third nodes respectively. BABA application was not associated with symptoms of phytotoxicity.     

The effect of β-aminobutyric acid on the growth of herbivorous insects feeding on Brassicaceae

dl ‐β‐Aminobutyric acid (BABA) is a nonprotein amino acid that can enhance defences in a variety of plants against a wide range of pathogens. BABA can also reduce infestation by phytopathogenic nematodes and has recently been shown to suppress the growth of aphids feeding on legumes. This investigation examined the effect of applying BABA as a root drench to a range of Brassicaceae, including Arabidopsis thaliana, on the performance of two species of aphid (Myzus persicae and Brevicoryne brassicae) and the larvae of two species of Lepidoptera (Trichoplusia ni and Plutella xylostella). Application of BABA reduced the performance of all four insect species, and inhibition of insects occurred on all the plants tested. The results illustrate that BABA‐induced resistance (BABA‐IR) can affect generalist and specialist insect herbivores and inhibit insects feeding with mandibulate as well as sap‐feeding mouthparts. The BABA‐induced suppression of B. brassicae and P. xylostella feeding on A. thaliana provides a means to further examine the mechanisms of BABA‐IR to insects using this model plant.     

DL‐β‐Aminobutyric acid application negatively affects reproduction and larval development of the rosy apple aphid,Dysaphis plantaginea,on apple

The rosy apple aphid, Dysaphis plantaginea (Passerini) (Hemiptera: Aphididae), is one of the major pests of European apple orchards, commonly controlled by the use of synthetic insecticides. In the present work, the non‐protein amino acid DL‐β‐aminobutyric acid (BABA), known to induce plant resistance against a wide range of abiotic and biotic stresses, has been tested for its protective effect against this pest on apple. We first verified the lack of any contact effect of BABA on the insect itself. Next we applied BABA as a soil drench to apple and monitored its effect on the population development of aphids after artificial infestation. We demonstrated that BABA strongly reduced the population growth and that this compound severely affected various life‐history characteristics of the aphid such as female longevity and fecundity, nymph mortality, and larval development.     

Application of DL-beta-aminobutyric acid (BABA) as a root drench to legumes inhibits the growth and reproduction of the pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae)

DL-beta-aminobutyric acid (BABA) is a non-protein amino acid that is an effective inducer of resistance against a variety of plant pathogens. However, examples of BABA-induced resistance against insect herbivores have not been reported. We applied BABA as a soil drench to legumes and monitored its effects on the pea aphid Acyrthosiphon pisum (Harris). On tic bean (Vicia faba var. minor), BABA increased aphid mortality, caused a reduction in the mean relative growth rate of individual insects and lessened the intrinsic rate of population increase (rm). BABA also caused significant reductions in the growth rate of A. pisum on pea (Pisum sativa), broad bean (Vicia faba var. major), runner bean (Phaseolus coccineus), red clover (Trifolium pratense) and alfalfa (Medicago sativa). No direct toxic effects of BABA against A. pisum were found, and no phytotoxic effects that may have caused a reduction in aphid performance were detected. Possible mechanisms behind this BABA-induced inhibition of aphid performance are discussed.     

β-Aminobutyric Acid-induced Resistance in Brassica juncea against the Necrotrophic Pathogen Alternaria brassicae

β‐Aminobutyric acid (BABA) pretreatment of Brassica plants protected them against the necrotrophic pathogen Alternaria brassicae. The achieved resistance level was much higher than that seen after salicylic acid (SA) and jasmonic acid (JA) pretreatments. BABA pretreatment to the leaves, 1 day before inoculation, led to an inhibition of the oxidative burst and a decrease in SA levels, but did not influence lipoxygenase activity nor cause callose deposition at the site of inoculation. Expression of two marker genes of the SA and JA pathways, namely PR1 and PDF1.2, was enhanced in response to BABA pretreatment. Our results indicate that BABA‐induced resistance is mediated through an enhanced expression of pathogenesis‐related protein genes, independent of SA and JA accumulation.     

BABA and Phytophthora nicotianae Induce Resistance to Phytophthora capsici in Chile Pepper (Capsicum annuum)

Induced resistance in plants is a systemic response to certain microorganisms or chemicals that enhances basal defense responses during subsequent plant infection by pathogens. Inoculation of chile pepper with zoospores of non-host Phytophthora nicotianae or the chemical elicitor beta-aminobutyric acid (BABA) significantly inhibited foliar blight caused by Phytophthora capsici. Tissue extract analyses by GC/MS identified conserved change in certain metabolite concentrations following P. nicotianae or BABA treatment. Induced chile pepper plants had reduced concentrations of sucrose and TCA cycle intermediates and increased concentrations of specific hexose-phosphates, hexose-disaccharides and amino acids. Galactose, which increased significantly in induced chile pepper plants, was shown to inhibit growth of P. capsici in a plate assay.     

Benzothiadiazole Induces Resistance to Plasmopara helianthi in Sunflower Plants

A novel synthetic chemical CGA 245704 [benzo (1,2,3) thiadiazole-7-carbothioic acid S methyl ester (acibenzolar-S-methyl) (BTH)] applied as a soil drench and foliar spray was shown to provide good protection against Plasmopara helianthi in sunflower plants. Soil drenches at the rates of 150 and 200 mg/kg soil, were applied 3 days before the inoculation and induced high levels of protection (80–82%) against downy mildew. At the highest concentrations (up to 300 mg/kg soil) about 90% protection was observed but at these rates phytotoxic symptoms were noted. This compound also provided good protection against P. helianthi when applied 1 day before the inoculation as well as when applied 1 day post-inoculation. The chemical had no antifungal activity in vitro against P. helianthi . In addition the combination of CGA 245704 and metalaxyl, as a seed dressing at low rates, provided a high level of control against the disease; however, the activity of this combination was not significantly different from metalaxyl alone. CGA 245704 applied as a soil drench and foliar spray also protected sunflower plants from P. helianthi foliar infection.     

Soil Drench Treatment with ?-Aminobutyric Acid Increases Drought Tolerance of Potato

The non-protein amino acid β-aminobutyric acid (BABA) is known to be a priming agent for a more efficient activation of cellular defence responses and a potent inducer of resistance against biotic and abiotic stresses in plants. Nevertheless, most of the studies on priming have been carried out in Arabidopsis. In potato, the effect of BABA was demonstrated only on biotic stress tolerance. We investigated the effect of BABA on the drought tolerance of potato and found that soil drenched with BABA at a final concentration of 0.3 mM improves the drought tolerance of potato. Water loss from the leaves of the primed plants is attenuated and the yield is increased compared to the unprimed drought-stressed plants. The metabolite composition of the tubers of the BABA-treated plants is less affected by drought than the tuber composition of the non-treated plants. Nitric oxide and ROS (reactive oxygen species) production is increased in the BABA-treated roots but not in the leaves. In the leaves of the BABA-treated plants, the expression of the drought-inducible gene StDS2 is delayed, but the expression of ETR1, encoding an ethylene receptor, is maintained for a longer period under the drought conditions than in the leaves of the non-treated, drought-stressed control plants. This result suggests that the ethylene-inducible gene expression remains suppressed in primed plants leading to a longer leaf life and increased tuber yield compared to the non-treated, drought-stressed plants. The priming effect of BABA in potato, however, is transient and reverts to an unprimed state within a few weeks.     

beta-Aminobutyric acid-induced protection of Arabidopsis against the necrotrophic fungus Botrytis cinerea

The non-protein amino acid beta-aminobutyric acid (BABA) protects numerous plants against various pathogens. Protection of Arabidopsis plants against virulent pathogens involves the potentiation of pathogen-specific defense responses. To extend the analysis of the mode of action of BABA to necrotrophs we evaluated the effect of this chemical on Arabidopsis plants infected with the gray mold fungus Botrytis cinerea. BABA-treated Arabidopsis were found to be less sensitive to two different strains of this pathogen. BABA protected mutants defective in the jasmonate and ethylene pathways, but was inactive in plants impaired in the systemic acquired resistance transduction pathway. Treatments with benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester, a functional analog of salicylic acid (SA), also markedly reduced the level of infection. Moreover, BABA potentiated mRNA accumulation of the SA-associated PR-1, but not the jasmonate/ethylene-dependent PDF1.2 gene. Thus, besides jasmonate/ethylene-dependent defense responses, SA-dependent signaling also contributes to restrict B. cinerea infection in Arabidopsis. Our results also suggest that SA-dependent signaling is down-regulated after infection by B. cinerea. The observed up-regulation of the PDF1.2 gene in mutants defective in the SA-dependent signaling pathway points to a cross-talk between SA- and jasmonate/ethylene-dependent signaling pathways during pathogen ingress.     

Induced Resistance by β‐Aminobutyric Acid in Artichoke against White Mould Caused by Sclerotinia sclerotiorum

β‐aminobutyric acid (BABA) was assessed for the ability to protect two artichoke cultivars, C3 and Exploter, against white mould caused by Sclerotinia sclerotiorum, which represents a major problem in the cultivation of this crop in many growing areas of Central Italy. Changes in the activity and isoenzymatic profiles of the pathogenesis‐related (PR) proteins β‐1,3‐glucanase, chitinase and peroxidase in plantlets upon BABA treatment and following inoculation of the pathogen in plantlets and leaves detached from adult plants were also investigated as molecular markers of induced resistance and priming. BABA treatments by soil drenching induced a high level of resistance against S. sclerotiorum in artichoke plantlets of both cultivars C3 and Exploter with a similar level of protection and determined a consistent increase in peroxidase activity paralleled with the differential induction of alkaline isoenzyme with a pI 8.6. A consistent change was found in Exploter in the peroxidase activity following BABA treatments and pathogen inoculation and was paralleled with the expression of an anionic band in plantlets and both anionic and cationic bands in leaves. Our results showed a correlation between BABA‐induced resistance (BABA‐IR) and a augmented capacity to express basal defence responses, more pronounced in cultivar C3 and associated β‐1,3‐glucanase accumulation in both plantlets and leaves inoculated with the pathogen, whereas chitinase resulted affected only at plantlet stage. The present results represent the first one showing the effect of BABA in inducing resistance in artichoke and associated accumulation of selected PRs. If confirmed in field tests, the use of BABA at early plant stages may represent a promising approach to the control soilborne pathogens, such as the early infection of S. sclerotiorum.     

Induction of systemic protection against rust infection in broad bean by saccharin: effects on plant growth and development

Here, we examine the effect of saccharin on the induction of systemic resistance in broad bean (Vicia faba) to the rust fungus Uromyces viciae-fabae. Saccharin was applied to beans at the three-leaf stage, either as a soil drench or by painting the solution on to first leaves. Plants were then challenge inoculated with the rust 1, 6, 10 and 14 d following saccharin treatment, after which they were harvested, assessed for the intensity of rust infection and plant growth measurements conducted. Foliar application of saccharin did not induce systemic protection to rust infection until 14 d after application and was less effective than saccharin applied as a soil drench. When saccharin was applied as a drench, systemic protection was not observed until 6 d after application, but was still apparent in plants 14 d after application of the drench. Irrespective of the method of application, saccharin had no significant effect on fresh and dry weights or leaf area of the plants. Saccharin applied as a drench did, however, reduce the number of leaflets produced.     

The effects of a plant defence priming compound, β-aminobutyric acid,on multitrophic interactions with an insect herbivore and a hymenopterous parasitoid

Biocontrol of aphids by natural enemies is utilized in many organic and integrated pest management schemes. β-aminobutyric acid (BABA), a non-protein amino acid, is a plant defence primer that suppresses growth of some insect herbivores when applied as a root drench. This investigation examined how applying BABA to host plants via the roots may impact on a parasitoid wasp of aphids. Female Aphidius ervi (Haliday) did not discriminate against pea aphids (Acyrthosiphon pisum (Harris)) reared on BABA-treated beans (Vicia faba L.) or show any modified responses to volatiles released from BABA-treated plants. BABA reduced the size of emerging wasps, primarily by inhibiting the growth of the host aphid. Metabolomic analysis revealed BABA in both aphids and emergent wasps indicating some potential for direct physiological inhibition to have occurred. Survival of the parasitoids was only reduced at doses of BABA likely to produce phytotoxic effects in many plant species, thus there may be potential to incorporate plant defence primers like BABA into integrated pest management practices. However, the precise mechanisms of BABA-inhibition of insects still require elucidation.