Chitinase Research Articles

Are ineffective defence reactions potential target for induced resistance during the compatible wheat-powdery mildew interaction?

Powdery mildew caused by Blumeria graminis f.sp. tritici, an obligate aerial biotrophic fungus, would be one of the most damaging wheat (Triticum aestivum) diseases without the extensive use of conventional fungicides. In our study, the expression levels of some basal defence-related genes were investigated during a compatible interaction in order to evaluate wheat reactions to infection, along with the different stages of the infectious process in planta. As fungal conidia initiated their germination and developed appressorial germ tube (AGT), early defence reactions involved the expression of a lipoxygenase (LOX)- and an oxalate oxidase (OXO)-encoding genes, followed by activations of corresponding LOX (EC 1.13.11.12) and OXO (EC 1.2.3.4) activities, respectively. When penetration of AGT took place, up-regulation of chitinases (CHI) and PR1-encoding genes expression occurred along with an increase of CHI (EC 3.2.1.14) activity. Meanwhile, expression of a phenylalanine ammonia-lyase-encoding gene also took place. Up-regulation of a phospholipase C- and lipid transfer proteins-encoding genes expression occurred during the latest stages of infection. Neither the phi glutathione S-transferase (GST)-encoding gene expression nor the GST (EC 2.5.1.13) activity was modified upon wheat infection by powdery mildew. Whether these defence reactions during such a compatible interaction are markers of immunity or susceptibility, and whether they have the ability to contribute to protection upon modulation of their timing and their intensity by resistance inducers are discussed.

Methyl jasmonate primes defense responses against Botrytis cinerea and reduces disease development in harvested table grapes

The effect of a postharvest treatment with 10μmol/L of methyl jasmonate (MeJA) on controlling gray mold decay caused by Botrytis cinerea in table grapes and the possible action mechanisms were investigated. The results indicated that MeJA treatment significantly reduced the incidence and development of gray mold decay in grapes. Meanwhile, MeJA treatment markedly enhanced activities of superoxide dismutase (SOD) and catalase (CAT), decreased ascorbate peroxidase activity, promoted the accumulation of H2O2 and improved the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. MeJA treatment also significantly enhanced activities of defense related enzymes including chitinase (CHI), β-1,3-glucanase (GNS), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD). Moreover, transcripts of defense related genes encoding CHI, GNS, PAL, SOD and CAT were only significantly enhanced in fruit pre-treated with MeJA and then inoculated with B. cinerea compared with those that were only treated with MeJA or inoculated with B. cinerea. These results suggested that 10μmol/L of MeJA treatment primes defense responses for enhanced disease resistance against Botrytis cinerea and thus reducing gray mold decay in harvested table grapes.

Inhibition of SlMPK1, SlMPK2, and SlMPK3 Disrupts Defense Signaling Pathways and Enhances Tomato Fruit Susceptibility to Botrytis cinerea.

Mitogen-activated protein kinases (MAPKs) are major components of defense signaling pathways that transduce extracellular stimuli into intracellular responses in plants. Our previous study indicated that SlMPK1/2/3 were associated with nitric oxide-induced defense response in tomato fruit. In this study, we determine whether SlMPK1/2/3 influence the tomato fruit's innate immunity and whether plant hormones and reactive oxygen species (ROS) are involved in SlMPK1/2/3 defense signaling pathways. Treatment with 10 μM U0126 significantly inhibited the relative expression of SlMPK1, SlMPK2, and SlMPK3 (P < 0.05). U0126-treated fruit showed higher concentrations of auxin indole acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GA), but a lower concentration of methyl jasmonate (MeJA). The activities of defense enzymes, including β-1,3-glucanases (GLU), chitinase (CHI), phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO), decreased after U0126 treatment. Meanwhile, H2O2 content increased, and catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) activities decreased after U0126 treatment. U0126 treatment enhanced the susceptibility of tomato fruit to Botrytis cinerea and resulted in more severe gray mold rot. These results demonstrate that inhibition of SlMPK1/2/3 disrupts tomato fruit defense signaling pathways and enhances the susceptibility to B. cinerea and also that plant hormones and ROS are associated with SlMPK1/2/3 defense signaling pathways.

Hot air treatment induces resistance against blue mold decay caused by Penicillium expansum in sweet cherry (Prunus cerasus L.) fruit

Effect of hot air (HA) treatment (44°C, 114min) on reducing blue mold decay caused by Penicillium expansum in sweet cherry fruit was investigated. The results indicated that fruit treated with HA had significantly lower disease incidence and smaller lesion diameter than the control fruit did. HA treatment significantly enhanced activities of chitinase (CHI) and β-1, 3-glucanase (GLU). The activities of polygalacturonase (PG) and pectinmethylesterase (PME) were significantly inhibited by HA treatment. Fruit treated with HA exhibited remarkably higher activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenoloxidase (PPO) and lower activity of ascorbate peroxidase (APX) than control. Expression of defense related genes such as PaGLU, PaCAT, and PaNPR1-like was greatly induced in HA-treated fruit during storage, while the expression of expansins (EXP) was down-regulated by HA treatment. These results suggest that HA can effectively inhibit blue mold decay caused by P. expansum in harvested cherry fruit possibly by directly inducing disease resistance and delaying fruit tissue softening that helps to ward off the spread of pathogens.

Characterization of the watermelon seedling infection process by Fusarium oxysporum f. sp. niveum

Fusarium oxysporum f. sp. niveum (FON) is the causal pathogen of fusarium wilt in watermelon. Understanding the interactions of watermelon seedlings and FON is of scientific and practical importance for disease control. The colonization dynamics of a susceptible watermelon cultivar, Sumi 1 (SM 1), were visualized using a green fluorescent protein (GFP)‐expressing strain of FON race 1 (FON 1‐GFP). Within 2 days post‐inoculation (dpi), hyphae adhered to and grew on epidermal cells. At 3 dpi, hyphae crossed the epidermis, penetrated into the cortex and progressed through parenchymal cell borders reaching the xylem vessels at 7 dpi. Growth of hyphae was restricted to the xylem vessels even in the colonized lower hypocotyl. The responses of SM 1 seedlings to infection were analysed. In the roots of SM 1, infected xylem vessels were plugged with gums and tyloses and some occluded vessels were shed from the root vascular tissue. Parenchyma cells surrounding the vascular cylinder showed wall thickening and cell disintegration, which eventually formed cavities. Hypocotyls of most SM 1 plants were also infected. Vascular tissues were densely colonized by hyphae until the vascular bundle became hollow and plants withered. Moreover, the expression patterns of six defence‐related genes in roots of SM 1 were analysed using real‐time quantitative PCR. Transcript levels of plant defensin‐like genes ClPDF2.1 and ClPDF2.4, phenylalanine ammonia lyase (PAL), chitinase (CHI) and ascorbate peroxidase (APX) were significantly induced in SM 1 roots during FON 1 infection, while polyphenoloxidase (PPO) did not show significant responses to FON 1 infection.

Effect of Organic Manure in the Induction of Resistance of Citrus to Phytophthora parasitica

Gummosis and root rot caused by Phytophthora are among the most economically important diseases in Citrus. Chemical control has been used; however, it is essential to search for new alternatives for its control. This study aimed to: (i) produce an organic compound from the anaerobic fermentation of cattle manure, (ii) determine the microbial diversity present in the compound, (iii) determine the effect of compound on mycelial growth of Phytophthora parasitica (P. nicotianae), (iv) evaluate its effect in inducing resistance to the pathogen in five Citrus rootstocks and, (v) evaluate the expression profile of some defense-related genes in resistant plants of Poncirus trifoliata and susceptible plants of Caipira sweet orange. The largest microbial population occurred between 25 and 35 days after production of organic manure with predominance of Bacillus spp. The organic manure at concentration of 20% inhibited about 80% of the mycelial growth of P. parasitica. Plants of Caipira sweet orange (susceptible to P. parasitica) when treated with organic manure at all concentrations (10, 20 and 50%), had lower disease severity when compared with the respective control. The analysis of gene expression suggested that the combination of treatment followed by inoculation with the pathogen in plants of Caipira sweet orange, the susceptible genotype, was able to increase the expression level of the genes encoding chitinase (CHI), lipoxygenase (LOX), peroxidase (POX), B-1,3-glucanase and chalcone synthase (CHS). It is believed that they should be involved with the resistance of Citrus plants to P. parasitica.

Plant Growth‐promoting Fungus Penicillium oxalicum Enhances Plant Growth and Induces Resistance in Pearl Millet Against Downy Mildew Disease

AbstractPlant Growth‐promoting Fungus (PGPF) Penicillium oxalicum was isolated from rhizosphere soil of pearl millet and was tested for its ability to promote growth and induce systemic resistance in pearl millet against downy mildew disease. The fungal isolate P. oxalicum UOM PGPF 16 was identified as P. oxalicum using ITS sequencing and morphological analysis and sequence was deposited at NCBI with accession number KF150220. Pearl millet susceptible seeds were treated with three different inducers (CS, CF and LCF) of PGPF P. oxalicum and all the inducers significantly reduced the downy mildew disease and enhanced plant growth. Among the inducers tested, CS treatment recorded highest seed germination of 91% and 1427 seedling vigour followed by LCF and CF treatments. The vegetative growth parameter and NPK uptake studies under greenhouse conditions revealed that the CS treatment of P. oxalicum remarkably enhanced the parameters tested when compared to control plants. A significant disease protection of 62% and 58% against downy mildew disease was observed in plants pretreated with CS of P. oxalicum under greenhouse and field conditions, respectively. The spatio‐temporal studies revealed that inducers P. oxalicum required a minimum of 3 days for developing maximum disease resistance which was maintained thereafter. The maximum Peroxidase (POX) activity (62.7 U) was observed at 24 h in seedlings treated with CS of PGPF P. oxalicum and the activity gradually reduced at later time points after pathogen inoculation. Chitinase (CHT) activity was significantly higher in inducer treated seedlings when compared to control seedlings inoculated with pathogen after 48 h and remained constant at all time points.

Photosynthetic and antioxidative alterations in coffee leaves caused by epoxiconazole and pyraclostrobin sprays and Hemileia vastatrix infection

Coffee leaf rust (CLR), caused by Hemileia vastatrix, is a major disease affecting coffee production worldwide. In this study, an in-depth analysis of the photosynthetic performance of coffee leaves challenged or not with H. vastatrix and sprayed with either epoxiconazole (EPO) or pyraclostrobin (PYR) was performed by combining chlorophyll a fluorescence images, photosynthetic pigment pools and the activities of chitinase (CHI), β-1,3-glucanase (GLU), peroxidase (POX) and catalase (CAT). The CLR severity was higher in the control plants, but reduced in plants sprayed with both PYR and EPO. Also, the CLR severity was reduced in plants sprayed with PYR compared with plants sprayed with EPO. Plants sprayed with either EPO or PYR showed maximal photosystem II quantum efficiency (Fv/Fm) values ranging from 0.78 to 0.80, which were quite similar to those obtained with inoculated plants (values ranging from 0.74 to 0.77). The decreases in the Fv/Fm ratio values and parallel increases in the F0 values in the inoculated plants, which were not observed in the control plants (sprayed with water) and were confirmed by images of the initial fluorescence (F0) and Fv/Fm parameters in the regions of the leaf tissue containing pustules and in the asymptomatic leaf tissue, indicated that photosynthesis was negatively impacted. When effective photosystem II quantum yield (Y(II)) values approached zero with a high photosynthetic photon flux density, high values of quantum yield of regulated energy dissipation (Y(NPQ)) in association with a high carotenoid concentration were noted in the inoculated plants sprayed either with PYR or EPO. The increased CLR severity in inoculated plants in contrast to inoculated plants sprayed with either PYR or EPO was associated with greater POX activity and a reduced photosynthetic pigment concentration. POX and CAT activities were increased in inoculated plants sprayed with either EPO or PYR when compared with control plants. CHI and GLU activities were maintained at high levels in the leaves of inoculated plants, regardless of the fungicide sprayed, indicating that CHI and GLU are less important for coffee resistance against CLR. The results of the present study clearly demonstrated that plants sprayed with either EPO or PYR showed milder CLR symptoms with adequate photosynthetic performance and optimal conditioning of their antioxidant systems.

Defence‐Related Enzymes in Soybean Resistance to Target Spot

AbstractTarget spot, caused by the fungus Corynespora cassiicola, has become a serious foliar disease in soybean production in the Brazilian Cerrado. Information in the literature regarding the biochemical defence responses of soybean to C. cassiicola infection is rare. Therefore, the objective of this study was to determine the biochemical features associated with soybean resistance to target spot. The activities of chitinases (CHI), β‐1‐3‐glucanases (GLU), phenylalanine ammonia‐lyases (PAL), peroxidases (POX), polyphenol oxidases (PPO) and lipoxygenases (LOX), as well as the concentrations of total soluble phenolics (TSP) and lignin‐thioglycolic acid (LTGA) derivatives, were determined in soybean leaves from both a resistant (FUNDACEP 59) and a susceptible (TMG 132) cultivar. The target spot severity, number of lesions per cm2 of leaflet and area under the disease progress curve were significantly lower for plants from cv. FUNDACEP 59 compared to plants from cv. TMG 132. The GLU, CHI, PAL, POX and PPO activities and the concentration of LTGA derivatives increased significantly, whereas LOX activity decreased significantly on the leaves infected by C. cassiicola. Inoculated plants from cv. FUNDACEP 59 showed a higher PPO activity and concentrations of TSP and LTGA derivatives at 4 and 6 days after inoculation compared to plants from cv. TMG 132. In conclusion, the results of this study demonstrated that the defence‐related enzyme activities increased upon C. cassiicola infection, regardless of the basal level of resistance of the cultivar studied. The increases in PPO activity and concentrations of TSP and LTGA derivatives, but lower LOX activity, at early stages of C. cassiicola infection were highly associated with soybean resistance to target spot.

Yeast Cell Surface Display of Bacterial Chitinase as a New Approach for Biocontrol of Phytopathogenic Fungi

Bacterial chitinase (EC 3.2.1.14) is a potential biological pesticide, but its biochemical properties for agricultural usage need to be improved. We adopted a new approach for using chitinase as a biocontrol application by immobilization of chitinase onto a yeast cell surface. To display the enzyme on the surface of Saccharomyces cerevisiae, a bacterial chitinase gene of Bacillus circulans No.4.1, was fused with the 3’ half terminus of α-agglutinin and the glycosylphosphatidylinositol (GPI) anchored signal. The yeast surface display with chitinase hydrolyzed p-nitrophenyl-diacetyl-chitobiose up to 3- to 4-fold higher than that without chitinase on the cell surface and the enzyme activity was active for up to 20 hr. Our results demonstrated that chitinase was successfully displayed on the yeast cell surface in an active form with an antifungal activity against phytopathogenic fungi, especially Fusarium oxysporum. This new approach may provide an evident for a potential biocontrol against phytopathogenic fungi.

Methyl Jasmonate Primed Defense Responses Against Penicillium expansum in Sweet Cherry Fruit

The effect of methyl jasmonate (MeJA) treatment on controlling blue mold decay caused by Penicillium expansum in sweet cherry fruit and the possible mechanisms were investigated. The results indicated that fruit treated with MeJA had significantly lower disease incidence and smaller lesion diameter than the control fruit did. The in vitro experiment showed that MeJA transiently inhibited spore germination and germ tube elongation of P. expansum. It is clear that MeJA triggers a priming mechanism in sweet cherry fruit, since only in fruit that had been pretreated with MeJA and then challenged with P. expansum was an enhanced capacity to augment defense responses observed. These augmented responses included enhanced activities of chitinase (CHI) and β-1,3-glucanase (GLU), and increased gene expression levels of catalase (CAT), calmodulin (CaM), GLU, phenylalanine ammonia-lyase (PAL), nonexpressor of pathogenesis-related genes 1 (NPR1-like), and thaumatin-like (THAU). Moreover, MeJA inhibited the increase of activities of polygalacturonase (PG) and pectinmethylesterase (PME). These results suggest that the efficacy of MeJA on controlling blue mold decay in sweet cherry fruit may be related to the transient direct inhibitory effect against the pathogens, suppressed activities of PG and PME, and the priming of defense responses.

Functional validation of plant transformation vector with stacked ech42 and bgn from Trichoderma in tomato for fungal disease resistance

Transgenic tomato lines (cv. Pusa Ruby) were generated by using Agrobacterium tumefaciens strain LBA4404 harboring endochitinase (ech42) and endoglucanase (bgn) genes stacked in binary vector (pRAGS121). Ten putative transformants in T0 generation were confirmed by PCR. Progenies of two transgenic tomato lines, CG2 and CG7 showed the presence of transgenes in the T1 generation. Transgene integration and copy number of transgene was assessed using PCR, Dot blot, Southern hybridization in T2 generation. Southern hybridization using DIG-labelled ech42 specific probe revealed the presence of two copies of transgenes. RT-PCR showed expression of ech42 and bgn at transcript level. Chitinase and glucanase assay revealed 4.09 and 3.93 fold higher expression of ech42 and bgn respectively in transgenic plant compared to nontransgenic plant. Bioassay of transgenic plant against Alternaria solani showed 2.97 times reduction in the leaf area infection and against Sclerotium rolfsii showed significant growth inhibition compared to non-transgenic control.

Eliciting Plant Defense on Anthracnose Disease in Chili (Capsicum annuum Linn.) by Sodium Nitroprusside Solution

The study on the induction of plant defense against to anthracnose disease of chili by sodium nitroprusside solution was investigated during pre- and post-harvest. Pre-harvest treatment was conducted by spraying the chili plants with sodium nitroprusside (SNP, nitric oxide donor) solution at 0 (control), 0.05 and 0.1 mM every 3 days for 9 times before inoculating with the spore suspension of Colletotrichum gloeosporioides (the causal agent of anthracnose disease) and then sprayed with SNP again 1 time after inoculating. The results revealed that 0.1 mM SNP was the best concentration to suppress anthracnose disease by reducing disease incidence and disease index on chili leaves, and showing the lowest loss of yield caused by anthracnose disease. This founding also showed that either pathogenic inoculation or SNP treatment had ability to induce the activities of peroxidase (POD) and phenylalanine ammonia lyase (PAL) of chili leaves, particularly the chili plant inoculated with pathogenic fungi followed by treated with 0.1 mM SNP showed the highest POD and PAL activities. Post-harvest treatment was done by inoculating the mature chilli fruit with C. capcisi for 4 h and followed by dipping in 0 (control) and 4 mM SNP. All fruit samples were kept at 13C for 15 days. The results showed that chili fruit dipped with 4 mM SNP reduced disease incidence, disease index, delayed weight loss, respiration rate, ethylene production, and also maintained the changes of fruit color (ΔE) better than non-treated fruit (control). The activities of chitinase (CHI) and β-1,3-glucanase (GLU) in chili fruit were induced by SNP with the highest peak on day 6 of storage but they were not significant different with the control fruit. These results indicated that SNP might potential leading to the reduction of anthracnose disease in chili by eliciting plant defense related enzymes in both pre- and post-harvest periods.

Cooperative effects of hydrogen sulfide and nitric oxide on delaying softening and decay of strawberry

Abstract: Hydrogen sulfide (H2S) and nitric oxide (NO) as two signal molecules play prominent roles in plant response to biotic stress. The combination effects of these two molecules on ripening and decay of postharvest strawberry were investigated. Strawberries were first dipped in distilled water, 0.8 mmol/L NaHS solution, 5 µmmol/L sodium nitroprusside (SNP) solution, and combinative solutions of 0.8 mmol/L NaHS and 5 µmmol/L SNP for 10 min, respectively, and then stored at 20°C. Results showed that the effects of the co-treatment of 0.8 mmol/L NaHS solution and 5 µmmol/L SNP solution were superior to that of other treatments. The former could suppress the percentage of fruit decay, inhibit respiration rate, maintain the original crust color, and slow down the decrease of firmness and the change of relative conductivity, which preserved the fruit quality. Further investigation showed that co-treatment of hydrogen sulfide and nitric oxide maintained higher activities of chitinase (CHI) and beta-1,3-glucanase (GNS), and lowered activities of pectin methylesterase (PME), polygalacturonase (PG) and endo-β-1,4-glucanase (EGase). The study indicated that the synergistic function of H2S and NO could effectively prolong the shelf life and reduce the decay rate of harvested strawberry. Keywords: hydrogen sulfide, nitric oxide, strawberry, enzyme activities, shelf life DOI: 10.3965/j.ijabe.20140706.014 Citation: Zhang C, Shi J Y, Zhu L P, Li C L, Wang Q G. Cooperative effects of hydrogen sulfide and nitric oxide on delaying softening and decay of strawberry. Int J Agric & Biol Eng, 2014; 7(6): 114－122

Presence of chitinase enzymes in crocodilians

Chitin is an abundant bio-polymer present as a structural component of many organisms such as arthropods, nematodes, mollusks, insects, and fungi, among others. Chitinolytic enzymes are synthesized for organisms to defend themselves against chitin-containing pathogens. Chitotriosidase (CHT) is a chitinase enzyme and one of the main proteins secreted by activated macrophages. It plays an important role in mechanisms of immunity by hydrolyzing chitin, thus protecting against chitin-containing pathogens. In this study, CHT was detected in Caiman latirostris plasma, and characterized under laboratory controlled conditions of temperature, reaction time, plasma concentration, pH and salinity. The results complement other immunological studies performed in caimans and demonstrate that they possess an efficient and well-developed immune system that resists the attack of some pathogens. Based on the current knowledge of the properties and homologies of CHT, it would be highly valuable to evaluate its possible therapeutic application in the veterinary clinical setting.

Cyclic LIPopeptides from Bacillus subtilis ABS-S14 elicit defense-related gene expression in citrus fruit.

Effects of cyclic lipopeptides (CLPs) obtained from Bacillus subtilis ABS-S14 on eliciting defense-related gene transcription and activity of defense-related enzymes; glucanase (GLU), chitinase (CHI), peroxidase (POX) and lipoxygenase (LOX) in Citrus sinensis cv. Valencia fruit were determined. The maximum level of GLU transcripts induced in fruit treated with fengycin was significantly greatest among treatments at 48 h. Surfactin enhanced the LOX and POX transcripts. In parallel, corresponding enzyme activities were correlated with changes in gene expression observed in fruit inoculated with Penicillium digitatum following treatment with individual CLPs. Synergistic effects of fengycin and iturin A, fengycin and surfactin were shown in gene transcript of GLU and CHI, respectively, and surfactin induced POX and LOX gene expression of citrus flavedo without pathogen infection. These results suggest that fengycin and surfactin act as elicitors of defense-related gene expression in “Valencia” fruit following infection.

Reduction of postharvest anthracnose and enhancement of disease resistance in ripening mango fruit by nitric oxide treatment

Nitric oxide (NO) acts as an important signal molecule with diverse physiological functions in plants. In this study we investigated the effects and possible mechanisms of exogenous NO on anthracnose caused by Colletotrichum gloeosporioides in mango fruit. ‘Guifei’ mango fruit were treated with NO donor (sodium nitroprusside of 0.1mM) at 25°C for 5min, inoculated with spore suspension of C. gloeosporioides after 24h of NO treatment, and stored at ambient temperature (25°C). NO treatment effectively suppressed lesion development on mango fruit inoculated with C. gloeosporioides, and lesion diameters at 2 through 8d in NO-treated fruit averaged 30% lower than those in control fruit. Additionally, NO treatment reduced natural anthracnose incidence and severity of mango fruit ripened at ambient temperature, and the values of both parameters from 4 to 10d of storage in NO-treated fruit averaged 40 and 45% lower, respectively, than those for control fruit. NO did not exhibit in vitro antifungal activity against C. gloeosporioides. NO treatment enhanced the activities of defense-related enzymes including phenylalanine ammonia-lyase (PAL), cinnamate-hydroxylase (C4H), 4-coumarate: CoA ligase (4CL), peroxidase (POD), β-1,3-glucanase (GLU) and chitinase (CHT). NO treatment also promoted the accumulation of total phenolics, flavonoids and lignin that might contribute to inhibition of the pathogen. In addition to antifungal efficacy, NO treatment delayed flesh softening, yellowing, and changes in soluble solids content (SSC) and titratable acidity (TA), and peaks of respiration rate and ethylene production during ripening. These results suggest that the resistance of NO-treated mango to anthracnose may be attributed to activation of defense responses as well as delay of ripening.

Influence of hot water treatment on brown rot of peach and rapid fruit response to heat stress

Recent results on hot water as an alternative treatment open a new perspective in disease incidence reduction. In the present work peach fruit were wounded, inoculated with conidia of Monilinia laxa and 15min, 3, 6, 12, 24 and 48h after inoculation treated by dipping in hot water (HT) at 60°C for 20s. The effect of heat treatment on some cell wall genes involved in ripening such as β-galactosidase (β-GAL), pectin lyase (PL), polygalacturonase (PG) and pectin methyl esterase (PME), was analyzed by qRT-PCR. The expression levels of defense related genes, phenylalanine ammonia lyase (PAL) and chitinase (CHI), heat stress-related genes such as heat shock proteins 70 and 90 (HSP70, HSP90), and reactive oxygen species (ROS) scavenging genes were also evaluated by qRT-PCR. A 100% disease incidence reduction, as compared to untreated fruit, was obtained by treating 6 and 12h after inoculation. Moreover, brown rot was inhibited by 85.7% when fruit were heat-treated 48h after inoculation. The expression levels of cell wall genes (β-GAL, PL, PG and PME) showed a general decrease in HT fruit as compared to the control, whereas PAL, CHI, HSP70 and ROS-scavenging genes increased their expression level in HT samples with respect to the untreated ones. Our results show a curative activity of heat on peach inoculated with M. laxa 48h before treatment. Each analyzed gene proved to be differentially expressed following heat treatment.

English

To evaluate the potential elicitor of homeopathic preparations on bean plants cv Carioca, homeopathics of Corymbia citriodora, Calcarea carbonica, Silicea and Sulphur in dynamisations 12, 24, 30 and 60CH were applied by pulverization throughout the aerial part. Samples of leaf tissue were taken at 6, 12, 24, 48 and 126 h after the treatment (HAT) to analyze the activity of peroxidase (POX), catalase (CAT), chitinase (CHI) and b-1.3-glucanase (GLU), and fifteen days after the application for the total contents of chlorophyll a and b. For the induction of phytoalexin phaseolin, seeds of the same genotype were germinated in the presence of respective treatments, and the production of phytoalexin quantified spectrophotometrically. All treatments increased the activity of POX, CAT, QUI and GLU, in at least one of the schedules evaluated in comparison to the control. The treatments C. citriodora and C. carbonic did not alter the contents of chlorophyll but induced the accumulation of phaseolin. Silicea and Sulphur caused significant reduction in the levels of chlorophyll a and b. The induction values were superior to the trading inductor (harpin), indicating that these homeopathies may come to be utilized as elicitor treatments on bean plants. The results indicate the potential of the treatments applied in the induction of biochemical mechanisms of defense in the bean plants. &nbsp; Key words: Resistance induction, homeopathy, enzymes, phytoalexins.

Inhibition on brown rot disease and induction of defence response in harvested peach fruit by nitric oxide solution

Nitric oxide (NO) is an important signal molecule involved in numerous plant responses to biotic and abiotic stresses. The effect of nitric oxide (NO) solution on pathogen infection and defence response of peach (Prunus persica (L.) Batsch) fruit against brown rot disease caused by Monilinia fructicola was investigated. The results showed that 15 μmol l−1 NO solution did not significantly inhibit spore germination, germ tube length or pathogenicity of M. fructicola, but significantly reduced disease incidence and lesion areas in the fruit. Although 100 μmol l−1 NO solution effectively inhibited the spore germination, germ tube elongation and pathogenicity of M. fructicola, the high concentration of NO solution caused damage to the fruit. Moreover, 15 μmol l−1 NO enhanced the activities of chitinase (CHI) and β-1,3-glucanase (GNS) in the fruit. RT-PCR analysis showed that the expression of four genes, CHI, GNS, pathogenesis-related protein 1 and 10 genes (PR-1, PR-10) all increased after NO treatment. Conversely, pretreatment with 100 μmol l−1 NO scavenger, 2-4-carboxyphenyl-4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), rendered the fruit relatively susceptible to pathogen infection and inhibited the defence response of the fruit. These results suggest that NO solution treatment can protect peach fruit from pathogen infection by inducing the activities of the defence enzymes and the expression of PR genes.