Plant Defense-related Enzymes Research Articles

Leaf litter from Cynanchum auriculatum Royle ex Wight leads to root rot outbreaks by Fusarium solani, hindering continuous cropping.

Cynanchum auriculatum Royle ex Wight (CA) is experiencing challenges with continuous cropping obstacle (CCO) due to soil-borne fungal pathogens. The leaf litter from CA is regularly incorporated into the soil after root harvesting, but the impact of this practice on pathogen outbreaks remains uncertain. In this study, a fungal strain D1, identified as Fusarium solani, was isolated and confirmed as a potential factor in CCO. Both leave extract (LE) and root extract (RE) were found to inhibit seed germination and the activities of plant defense-related enzymes. The combinations of extracts and D1 exacerbated these negative effects. Beyond promoting the proliferation of D1 in soil, the extracts also enhanced the hypha weight, spore number, and spore germination rate of D1. Compared to RE, LE exhibited a greater degree of promotion in the activities of pathogenesis-related enzymes in D1. Additionally, caffeic acid and ferulic acid were identified as potential active compounds. LE, particularly in combination with D1, induced a shift in the composition of fungal communities rather than bacterial communities. These findings indicate that the water extract of leaf litter stimulated the growth and proliferation of fungal strain D1, thereby augmenting its pathogenicity toward CA and ultimately contributing to the CCO process.

Influence of silver nanoparticles on postharvest disease, pericarp hardening, and quality of mangosteen

The main problem associated with mangosteen (Garcinia mangostana L.) in the postharvest period is fruit rot caused by Lasiodioplodia theobromae, which results in pericarp hardening, poor quality, and short storage life. Silver nanoparticles (AgNPs) constitute a potential agent for curbing microbial infections, especially fungal infections. In the in vitro test conducted in this study, 270 ppm AgNPs completely inhibited mycelium growth and spore germination (100 %) in L. theobromae, similar to the results obtained using 200 ppm fungicidal carbendazim. For the in vivo test, the concentration of AgNPs was increased to 300 ppm to provide a strong inhibitory effect against fungal infection on mangosteen fruit. The results showed that treatment with AgNPs significantly decreased the disease index (DI) in the artificially inoculated mangosteen fruit stored at 25ºC, and AgNP residue in the fruit was found to be 3.3 mg kg-1, which conforms to the Environmental Protection Agency (2009) regulations. Furthermore, the effects of AgNPs on fruit rot disease and plant defense-related enzymes were investigated with regard to naturally infected mangosteen stored at 13ºC for 30 days, as compared to fungicide-treated fruits and non-treated fruits (control). The results revealed that AgNP treatment resulted in an eight-fold reduction in fruit rot disease, whereas fungicidal treatment resulted in only a 2.46-fold disease reduction compared to the result in the control group. Also, AgNP treatment induced plant defense-related enzyme activities: phenylalanine ammonia-lyase (PAL), peroxidase (POD), chitinase (CHI) and β-1,3-glucanase (GLU), and ɑ-mangostin content (a major phenolic compound in pericarp). Further, the effect of AgNPs on the physiology and quality of fruits was measured and compared with the non-treated fruits. The results showed that AgNP treatment lowered ethylene production and rate of respiration, which resulted in a reduction in weight loss and pericarp hardening. AgNP treatment was also found to maintain pericarp color, chlorophyll content in calyx as well as total soluble solids (TSS), titratable acidity (TA), and anthocyanin content in the pericarp. This result implies that AgNPs constitute an effective and safe treatment modality for controlling fruit rot disease, reducing pericarp hardening, and maintaining the quality of mangosteen fruit.

Biocontrol potential of Pseudomonas rhodesiae GC-7 against the root-knot nematode Meloidogyne graminicola through both antagonistic effects and induced plant resistance

Plant-parasitic nematodes (PPNs) cause serious damage to agricultural production worldwide. Currently, because of a lack of effective and environmental-friendly chemical nematicides, the use of microbial nematicides has been proposed as an eco-friendly management strategy to control PPNs. A nematicidal bacterium GC-7 was originally isolated from the rice rhizosphere, and was identified as Pseudomonas rhodesiae. Treatment with the fermentation supernatant of GC-7 in vitro showed a highly lethal effect on second-stage juveniles of Meloidogyne graminicola, with the mortality rate increasing to 95.82% at 24 h and egg hatching significantly inhibited, with a hatch inhibition rate of 60.65% at 96 h. The bacterium significantly reduced the level of damage caused by M. graminicola infestations to rice (Oryza sativa) in greenhouse and field experiments. Under greenhouse conditions, the GC-7 culture efficiently reduced the gall index and nematode population in rice roots and soils, as well as inhibited nematode development compared to the control. Under field conditions, application of the GC-7 consistently showed a high biocontrol efficacy against M. graminicola (with a control efficiency of 58.85%) and promoted plant growth. In addition, the inoculation of GC-7 in M. graminicola-infested rice plant fields significantly suppressed final nematode populations in soil under natural conditions. Furthermore, activities of plant defense-related enzymes, peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase were remarkably increased in plant roots treated with GC-7 compared with roots that were challenge to M. graminicola. Moreover, quantitative real-time PCR analysis showed that GC-7 significantly enhanced the expression of defense genes (PR1a, WRKY45, JaMYB, AOS2, ERF1, and ACS1) related to salicylic acid, jasmonic acid, and ethylene signaling pathways in rice roots after inoculation with GC-7 at different levels. The results indicated that GC-7 could be an effective biological component in the integrated management of M. graminicola infecting rice.

Mycorrhizal Inoculation Enhances Nutrient Absorption and Induces Insect-Resistant Defense of Elymus nutans.

The majority of terrestrial plants can form symbiotic associations on their roots with arbuscular mycorrhizal fungi (AMF) in the soil to stimulate the growth and nutrient uptake of the host plant and to improve plant resistance to insects and disease. However, the use of AMF for insect control on gramineous forages requires further study. Here, we evaluated the effects of AMF (Funneliformis mosseae) inoculation on the defense against Locusta migratoria attack in Elymus nutans. Inoculation assays showed that mycorrhizal plants had a higher resistance than non-inoculated plants, as evidenced by plants having more plant biomass, a higher nitrogen and phosphorus content, and greater lipoxygenase (LOX) activity. The results of insect damage showed that in addition to a decrease in the enzyme phenylalanine-ammonia-lyase, the activities of other plant defense-related enzymes (including polyphenol oxidase and β-1,3-glucanase) were increased. A key enzyme, LOX, belonging to the jasmonic acid (JA) signaling pathway was notably increased in mycorrhizal treatment. Volatile organic compounds (VOCs) were identified using gas chromatography mass spectrometry and the results showed that several metabolites with insect-resistant properties, including D-Limonene, p-Xylene, 1,3-Diethylbenzene were detected in mycorrhizal plants. These findings suggest that mycorrhizal inoculation has potential applications in insect management on forage grasses and demonstrates that the JA signaling pathway is essential for insect resistance in Elymus nutans.

The Combined Effect of Hot Water Treatment and Chitosan Coating on Mango (Mangifera indica L. cv. Kent) Fruits to Control Postharvest Deterioration and Increase Fruit Quality

The synergistic effect of dipping in 55 °C for 5 min of hot water (HW) and 1% chitosan coating during the storage of mango at 13 ± 0.5 °C and 85%–90% relative humidity for 28 days was investigated. The combined treatment significantly suppressed the fruit decay percentage compared with both the single treatment and the control. In addition, the specific activities of key plant defense-related enzymes, including peroxidase (POD) and catalase (CAT), markedly increased. The increase occurred in the pulp of the fruits treated with the combined treatment compared to those treated with HW or chitosan alone. While the control fruits showed the lowest values, the combination of pre-storage HW treatment and chitosan coating maintained higher values of flesh hue angle (h°), vitamin C content, membrane stability index (MSI) percentage, as well as lower weight loss compared with the untreated mango fruits. The combined treatment and chitosan treatment alone delayed fruit ripening by keeping fruit firmness, lessening the continuous increase of total soluble solids (TSS), and slowing the decrease in titratable acidity (TA). The results showed that the combined application of HW treatment and chitosan coating can be used as an effective strategy to suppress postharvest decay and improve the quality of mango fruits.

Novel Genetic Dysregulations and Oxidative Damage in Fusarium graminearum Induced by Plant Defense Eliciting Psychrophilic Bacillus atrophaeus TS1.

This study elaborates inter-kingdom signaling mechanisms, presenting a sustainable and eco-friendly approach to combat biotic as well as abiotic stress in wheat. Fusarium graminearum is a devastating pathogen causing head and seedling blight in wheat, leading to huge yield and economic losses. Psychrophilic Bacillus atrophaeus strain TS1 was found as a potential biocontrol agent for suppression of F. graminearum under low temperature by carrying out extensive biochemical and molecular studies in comparison with a temperate biocontrol model strain Bacillus amyloliquefaciens FZB42 at 15 and 25 °C. TS1 was able to produce hydrolytic extracellular enzymes as well as antimicrobial lipopeptides, i.e., surfactin, bacillomycin, and fengycin, efficiently at low temperatures. The Bacillus strain-induced oxidative cellular damage, ultrastructural deformities, and novel genetic dysregulations in the fungal pathogen as the bacterial treatment at low temperature were able to downregulate the expression of newly predicted novel fungal genes potentially belonging to necrosis inducing protein families (fgHCE and fgNPP1). The wheat pot experiments conducted at 15 and 25 °C revealed the potential of TS1 to elicit sudden induction of plant defense, namely, H2O2 and callose enhanced activity of plant defense-related enzymes and induced over-expression of defense-related genes which accumulatively lead to the suppression of F. graminearum and decreased diseased leaf area.

Biocontrol Potential of Trichoderma afroharzianum TM24 Against Grey Mould on Tomato Plants.

Grey mould caused by Botrytis cinerea leads to severe economic loss on commercial tomato production. Application of beneficial microorganism offers an eco-friendly alternative for mitigation of tomato fungal disease damage, considering negative influences of fungicides. In the present study, an antagonistic Trichoderma afroharzianum isolate TM24 was evaluated for its biocontrol potential on tomato grey mould. The isolate TM24 showed obviously antagonistic effect on B. cinerea mycelium growth and production of glucanase and chitinase. Leaf spraying with spore suspension of isolate TM24 showed a biocontrol efficiency of over 54% against tomato grey mould in greenhouse pot experiment. The activities of plant defense-related enzymes including polyphenol oxidase, phenylalanine ammonialyase, superoxide dismutase, and peroxidase were all increased to varying degrees in tomato leaves after isolate TM24 treatment. Transcriptome analysis showed that, a total of 1941, 1753 and 38 differentially expressed genes (DEGs) were obtained at 24, 48 and 72 hpi, respectively, in tomato leaves pretreated with T. afroharzianum TM24, and then challenged with B. cinerea inoculation. The DEGs were mainly enriched in MAPK signaling pathway and plant hormones signal transduction pathway. Multiple genes that regulated crucial nodes of defense-related pathways, like flavonoid, phenylpropanoid, jasmonic acid and ethylene metabolisms were also identified, which may have positive correlations with the biocontrol potential of isolate TM24 in tomato plants. These promising results provided valuable information on using T. afroharzianum TM24 as a beneficial biocontrol agent in tomato grey mould management.

Genomic insights into biocontrol potential of Bacillus stercoris LJBS06.

The online version contains supplementary material available at 10.1007/s13205-021-03000-6.

An overview of plant defense-related enzymes responses to biotic stresses

Plants are the ecosystem's primary source and have a direct or indirect impact on human life. Pathogens and insect's interference into the plants contribute to enormous losses in yield and productivity. Pathogens that can invade plants capable of recognizing and responding to their attack by activating security systems. This activation requires signal transmission from the receptor to the cell gene. Recently, signal molecules have been discovered that are involved in signal transmission induced in response to biological stresses. Accumulated data indicate the presence of a dynamic and well-integrated bio-signal mechanism in plant cells. Controls plant defense responses to these net pathogen attacks.

FOLIAR SPRAYED-SILICON TO INDUCE DEFENSE-RELATED ENZYMATIC ACTIVITY AGAINST Pyricularia oryzae INFECTION IN AEROBIC RICE

Rice blast disease caused by Pyricularia oryzae is the most devastative disease. The alternative in rice blast disease management using foliar silicon (Si) application is gaining attention. The mechanism underlying defense-related enzyme induced through foliar Si application is still scarce. This research aimed to elucidate the bio-efficacy of foliar Si in inducing defense-related enzyme activity against P. oryzae in two aerobic rice cultivars: MR219-4 (blast-partially resistant) and MARDI Aerob 1 (resistant). Calcium silicate at 9 mg/L was foliar-sprayed and the disease severity index was evaluated and transformed to the area under disease progress curves (AUDPC). Foliar Si application significantly reduced rice blast disease severities in both cultivars tested. The AUDPC was reduced to 96.57 (MR219-4) and 21.90 (MARDI Aerob 1), from 148.57 (MR219-4) and
 53.73 (MARDI Aerob 1). Plant defense-related enzymes: peroxidase (PO), polyphenol oxidases (PPO), and phenylalanine ammonia-lyase (PAL) were increased and might be associated to increase resistance. Also, there was a significant interaction (p=0.003) between rice cultivar and treatment to Si content in rice leaf. Thus, foliar application of Si in rice seedling underlined the important role of Si as a modulator in influencing plant defense-related enzymes with interacting with other stress signaling pathways leading to induce resistance.

Trichoderma virens-Tv4 enhances growth promoter and plant defense-related enzymes of mungbean (Vigna radiata) against soil-borne pathogen Rhizoctonia solani

Abstract. Inayati A, Sulistyowati L, Aini LQ, Yusnawan E. 2020. Trichoderma virens-Tv4 enhances growth promoter and plant defense-related enzymes of mungbean (Vigna radiata) against soil-borne pathogen Rhizoctonia solani. Biodiversitas 21: 2410-2419. Trichoderma virens has been studied for its ability to control various soil-borne pathogens as well as to induce plant resistance. The ability of T. virens control R. solani and its capability to induce resistance was evaluated in two different genotypes of mungbean (Vigna radiata (L.) R. Wilczek). Plant growth-promoting capability and production of plant defense-related enzymes during plant-pathogen-Trichoderma interaction were investigated. Pathogen infection caused the morphological and biochemical changes as well as increased plant defense enzymes activity such as peroxidase, polyphenol oxidase, PAL, phenolics, and flavonoid compared to control uninoculated plants. T. virens improved mungbean seedling growth in terms of increased total biomass, root weight, and root length as well as improved chlorophyll content and IAA-synthase from leaves and roots. T. virens treatment alone or in the presence of pathogen-induced mungbean defense-related enzymes indicated by the increasing of PO and PPO activity, and higher accumulation of total phenolic and flavonoid content. Although most of plant induced resistance parameters showed low and non-significant in direct single-factor comparison, Pearson’s correlation showed there was a positive correlation between plant growth promoter compounds (IAA and chlorophyll) with plant defense-related enzymes (total phenol, and flavonoid content). T. virens treatment can induce systemic defense response of mungbean seedling directly by increasing the activity of some defense-related enzymes, and indirectly by improving plant health, and promoting plant growth. In conclusion, T. virens-Tv4 has potential to be developed as bio-control agents to control R. solani as well as to induce mungbean resistance.

Local Trichoderma strains as a control strategy of complex black root rot disease of strawberry in Egypt

BackgroundEconomics and human safety to avoid health risks caused by fungicides are materializing new era of biological pest control. Trichoderma species ranked high among other agents to control complex black root rot disease of strawberry caused by Fusarium solani, Rhizoctonia solani, and Pythium sp. Our study aimed to document the efficacy of local strains representing T. harzianum, T. viride, T. virinis, and T. koningii against such a disease.Materials/methodsThese strains were cultured separately on potato dextrose broth medium to test their inhibitory effect against strawberry black root rot in vitro and in vivo. Strawberry growth and yield were also assessed relative to the untreated check and the fungicide Actamyl. Activity of peroxidase and chitinase were measured in plant leaves using spectrophotometer.ResultsEach of the antagonistic fungal strains significantly reduced growth area of all pathogenic fungi collectively causing the disease. Trichoderma harzianum, T. viride, and T. koningii reduced the growth area more than 90.6% for all tested pathogenic fungi. Each species significantly reduced disease incidence and severity under field conditions. The highest reduction in the disease incidence and severity, 83.3 and 88.5% respectively, was attained by mixture of the four species. This mixture increased the strawberry fresh and dry weight by 83.3 and 176.9%, respectively, and the yield by 117.1%. All Trichoderma species tested significantly increased the activity of two plant defense-related enzymes of strawberry plants against the pathogens. Their mixture attained the highest increase of peroxidase and chitinase activity by 150 and 160.9%, respectively.ConclusionsWhile the fungal mixture could considerably increase the strawberry fresh and dry weight as well as the yield, it suppressed the incidence and severity of the disease. So, integrated pest management in ways that make these biocontrol agents complementary or superior to chemical fungicides should further be examined against this disease.

Bacillomycin D inhibits growth of Rhizopus stolonifer and induces defense-related mechanism in cherry tomato.

The inhibitory effect of Bacillomycin D, a cyclic lipopeptide, on Rhizopus stolonifer colonization of cherry tomato was studied, and its possible mechanism of action was explored. Bacillomycin D showed a direct inhibitory effect on R. stolonifer spore germination and mycelial growth in vitro. It conferred both a direct inhibitory effect on R. stolonifer growth in cherry tomato in vivo and induced host resistance in cherry tomato. Moreover, Bacillomycin D treatment significantly increased the activities of plant defense-related enzymes, including chitinase (CHI), β-1,3-glucanase (GLU), phenylalanine ammonia-lyase (PAL), and peroxidase (POD). Real-time PCR (RT-PCR) showed that defense-related genes involved in the salicylic acid defense signaling pathway and genes encoding pathogenesis-related proteins were up-regulated in Bacillomycin D treatment. Furthermore, Bacillomycin D-C16 resulted in direct inhibition and a remarkable induced resistance to R. stolonifer which was higher than as induced by Bacillomycin D-C14. Together, the data indicated that Bacillomycin D can control the growth of R. stolonifer through both the direct inhibition of the fungus and the activation of defense-related genes and enzymes in cherry tomato.

Co-inoculation of different antagonists can enhance the biocontrol activity against Rhizoctonia solani in tomato.

Biological control by using microbial inoculants is adopted as the best alternative to chemical pesticides to manage plant diseases. In the present study, a microbial consortia based management strategy involving the microbes Bacillus velezensis MB101 (BV), Streptomyces atrovirens N23 (SA) and Trichoderma lixii NAIMCC-F-01760 (TL), was evaluated for the management of Rhizoctonia solani (RS), the causal agent of tomato root rot. The efficacy of these microbial inoculants was evaluated in glasshouse and field experiments. Plant defense-related enzymes were assayed in the glasshouse, and biocontrol effect was evaluated in the field with RS infected soil. In the glasshouse experiment, co-inoculated SA + TL treated plants showed maximum disease resistance in comparison to control. Also, the plant defense-related enzymes such as chitinase, β-1,3-glucanase, peroxidases, polyphenol oxidase, and phenylalanine ammonia lyase were increased in this treatment. Furthermore, three application methods were assessed in the field, and SA + TL showed maximum disease reduction (76%) by the dual application. Based on glasshouse and field study results, it was concluded that co-inoculation of SA + TL activated plant defense against RS as compared to the individual microbes, and co-inoculation could be a new effective strategy to manage the root rot pathogen in an eco-compatible manner.

UV irradiation induces resistance against fruit rot disease and improves the quality of harvested mangosteen

Fruit rot disease and short shelf life are the limiting factors of mangosteen fruit. This study focused on investigating the effect of ultraviolet (UV) irradiation in controlling fruit rot disease and on quality improvement in harvested mangosteen. Mangosteen fruit artificially inoculated with L. theobromae were treated with UV-B or UV-C irradiation at dosages of 0 (control), 6, 13, 26, and 40 kJ m−2 and stored at 25 °C for 7 d. The results indicate that UV-C treatment exhibited higher fungicidal potential in preventing fruit rot disease than UV-B treatment. UV-C treatment at a dose of 13 kJ m-2 was the most effective in reducing disease incidence and lesion diameter, followed by UV-C at a dose of 26 kJ m−2, whereas the effects of UV-C at a higher dosage (40 kJ m−2) and a lower dosage (6 kJ m−2) showed no significant difference from the untreated fruit. Therefore, UV-C irradiation at doses of 13 kJ m−2 was selected to investigate the induction of disease resistance and improvement of mangosteen quality. Naturally infected mangosteen fruit were exposed to UV-C irradiation at a dose of 13 kJ m−2 and untreated fruit served as the control. All fruit samples were kept at 13 °C for 21 d. The results showed that UV-C treatment reduced fruit rot disease and induced the activity of key plant defense-related enzymes, including phenylalanine ammonia lyase (PAL), peroxidase (POD), chitinase and β-1,3-glucanase, besides increasing the content of total phenolics and hydrogen peroxide (H2O2). In addition, the fruit treated with UV-C could delay weight loss, respiration rate, color changes of peel and calyx and maintain total chlorophyll in the calyx of mangosteen. The results suggest that UV-C application is an alternative approach to suppress fruit rot disease and improve the postharvest quality of mangosteen.

Plant defense-related enzymes against pathogens: a review

Plant disease control is mainly based on the use of fungicides, bactericides, and insecticides-chemical compounds toxic to plant invaders, causative agents, or vectors of plant diseases. However, the detrimental effect of these chemicals or their degradation products on the environment and human health strongly imposes the search for novel, harmless means of disease control. Therefore, it is essential to introduce environmentally-friendly alternative measures for management of plant diseases. Induced plant resistance is one of the promising non-chemical strategies for the effective management of diseases. The host plant mediated resistance is governed by defense response genes encoding for production of various pathogenesis-related (PR) proteins. This review chiefly explains the biochemical response of plant defense mechanism pertaining to defense-related enzymes which have been identified as PR proteins.

Effect of increased UV-B radiation on biological control of the gray mold by Clonostachys rosea and on the expression of strawberry defense-related enzymes

Changes in UV-B radiation can have large effects on the management of the pathogen Botrytis cinerea, especially on strawberry production in Brazil. The aim of this work was to investigate the effect of the increased UV-B radiation on biological control of gray mold by Clonostachys rosea and on the expression of plant defense-related enzymes. The experiments were laid out in randomized complete blocks in a split-plot design. The whole-plot factor was represented by UV-B treatments: 1. ambient solar UV; 2. ambient solar UV reduced by 80% (UV-); 3 ambient solar UV supplemented with UV-B lamps (UV+). The split-plot factors were: 1. plants sprayed with water (control); 2. plants exposed to B. cinerea; 3 plants sprayed weekly with an inoculum suspension of C. rosea and exposed to B. cinerea. The latent infection of B. cinerea was evaluated during five weeks per season, after which leaves were collected to assess the peroxidase, polyphenoloxidase and chitinase activities. No significant effect on B. cinerea incidence for irradiation treatments were observed during both seasons, although C. rosea treatments have been able to control gray mold on fruits. The enzymatic activity was related to the ambient condition, not to the exposure of the plants to these micro-organisms. Only UV+ conditions led to an increase of polyphenoloxidase activity in season 2. The results indicate that the increase of UV-B radiation has no influence on the ability of C. rosae to control the gray mold on strawberry.

Combined treatment with hot water and UV-C elicits disease resistance against anthracnose and improves the quality of harvested mangoes

This research investigated the effects of hot water, UV-C irradiation and their combination on the induction of resistance to anthracnose disease and on quality improvement in harvested mangoes. Naturally infected mango fruits were harvested, surface-disinfested with a solution of 100 ppm sodium hypochlorite and air dried. The fruits were then treated with UV-C irradiation at a dose 6.16 kJ m−2, with hot water at 55 °C for 5 min or with hot water followed by UV-C irradiation. Untreated fruits served as the control. All fruit samples were kept at 13 °C for 12 days. The combined treatment significantly suppressed the severity of anthracnose symptoms compared with either single treatment. Additionally, the specific activities of key plant defense-related enzymes, such as phenylalanine ammonia lyase (PAL), peroxidase (POD), chitinase (CHI) and β-1,3-glucanase (GLU), increased in both the peel and the pulp of the mango fruits. The expressions of the MI-PAL, MI-POD, MI-CHI and MI-GLU genes in the mango peel were markedly enhanced in the fruits treated with the combined treatment in comparison with those treated with hot water or UV-C alone, while the control fruits showed the lowest expression of these genes. The combined treatment or UV-C treatment alone significantly delayed fruit ripening by maintaining fruit firmness, retarding the progressive increase of total soluble solids (TSS) and delaying the decrease in titratable acidity (TA). Weight loss was not significantly different among the treatments. The results suggested that the combination of hot water and UV-C treatment may be used as a tool not only for suppressing anthracnose disease but also for improving the quality of harvested mangoes by inducing the expression of plant defense-related genes.

Survival of Bemisia tabaci and activity of plant defense-related enzymes in genotypes of Capsicum annuum L.

The whitefly Bemisia tabaci (Gennadius, 1889) is a major plant pest of horticultural crops from the families Solanaceae, Fabaceae and Cucurbitaceae in Neotropical areas. The exploration of host plant resistance and their biochemical mechanisms offers an excellent alternative to better understand factors affecting the interaction between phytophagous insect and host plant. We evaluated the survival of B. tabaci in landrace genotypes of Capsicum annuum L., and the activity of plant defense-related enzymes (chitinase, polyphenoloxidase, and peroxidase). The landrace genotypes Amaxito, Tabaquero, and Simojovel showed resistance to B. tabaci, as we observed more than 50% nymphal mortality, while in the commercial susceptible genotype Jalapeno mortality of B. tabaci nymphs was not higher than 20%. The activities of plant defense-related enzymes were significantly different among pepper genotypes (P < 0.05). Basal activities of chitinase, polyphenoloxidase and peroxidase were significantly lower or equal in landrace genotypes than that of the commercial genotype Jalapeno. The activity of plant enzymes was differential among pepper genotypes (P < 0.05). For example, the activity of chitinase enzyme generally was higher in non-infested plants with B. tabaci than those infested. Instead polyphenoloxidase ('Amaxito' and 'Simojovel') and peroxidase enzymes activities ('Tabaquero') increased in infested plants (P < 0.05). We conclude that basal activities of plant defense-related enzymes could be act through other mechanism plant induction, since plant defense-related enzymes showed a different induction response to B. tabaci. We underlined the role of polyphenoloxidase as plant defense in the pepper genotype Simojovel related to B. tabaci.

Elevated expression of hydrolases, oxidase, and lyase in susceptible and resistant cucumber cultivars systemically induced with plant growth-promoting fungi against anthracnose

Susceptible and resistant cultivars of cucumber (cv. Suyo and cv. Shogoin fushinari, respectively) were evaluated for induction of systemic resistance by plant growth-promoting fungal isolates Phoma sp. GS8-1 and nonsporulating fungus GU21-2 against Colletotrichum orbiculare. Reduction in anthracnose disease was assessed at regular intervals of 0, 3, 6, and 9 days after challenge inoculation. Activities of endochitinase, β-1,3-endoglucanase, peroxidase (PO), polyphenol oxidase, and phenylalanine ammonia lyase (PAL) were assayed at the above intervals, while the activities of exochitinase and β-1,3-exogluconase were assayed at 9 days after challenge inoculation. The data showed that all the enzymes activities increased in plants treated with plant growth-promoting fungi (PGPF) compared with nontreated plants of both cultivars. The activities of endochitinase and β-1,3-endoglucanase were highly increased in PGPF-induced plants than in nontreated plants of both cultivars at different time points. Activities of PO, polyphenol oxidase, and PAL also increased between 3 and 6 days due to inoculation with PGPF and decreased thereafter. The activity of PAL at 9 days in PGPF-induced plants was at the same level as that of nontreated plants of both cultivars. Results of this investigation suggest that PGPF-induced systemic resistance is associated with not only high increases in the activities of chitinase and β-1,3-gluconases but also other plant defense-related enzymes such as PO, PPO, and PAL. Roles of other mechanisms rather than accumulation of defense-related enzymes in PGPF-mediated induced resistance in susceptible cultivars were demonstrated.