Biochemical Defense Responses Research Articles

Antioxidant and other biochemical defense responses of Macrotyloma uniflorum (Lam.) Verdc. (Horse gram) induced by high temperature and salt stress

High temperature and salinity are the major ecological factors challenging crop productivity in the arid and semiarid regions of the world. Effects of high temperature (43-45°C) and salt stress (0.6 M) on Macrotyloma uniflorum (Lam.) Verdc. (Horse gram), were evaluated in terms of antioxidants and antioxidant enzymes. Both treatments caused typical stress responses in this tropical leguminosae. Oxidative stress indicators such as H2O2, TBARS, and proline were significantly elevated. Similarly, the antioxidant enzymes superoxide dismutase (SOD; EC 1.15.1.1), guaiacol peroxidase (POX; EC 1.11.1.7) and acid phosphates (AP; EC 3.1.3.2) were significantly elevated while catalase (CAT; EC 1.11.1.6) was reduced. These treatments had contrasting effects on glutathione reductase (GR; EC1.6.4.2) and β-amylase (EC 3.2.1.1). While temperature stress caused increase in GR and decrease in β-amylase, salt stress caused a counter effect. Contrast was also observed in ascorbate and glutathione which increased in temperature stress and reduced in salt stress. SDS-PAGE analysis indicated entirely different protein profiles in temperature and salt stressed seedlings. Growth rate and fresh mass were affected to same extent, relative to their controls. Taken together these data describes the similarities and peculiarities of key biochemical responses of Horse gram to high temperatures and salinity.

Effects of chitosan-oil coating on blue mold disease and quality attributes of jujube fruits

The effects of chitosan coating enriched with cinnamon oil on blue mold disease and quality attributes were investigated. In the in vitro experiment, the results demonstrated that the antifungal activity against P. citrinum improved with increasing concentration of chitosan or cinnamon oil. In the in vivo study, chitosan-oil treatments significantly reduced fungal decay caused by P. citrinum and all compounds with cinnamon oil at 2.0% showed complete control of the growth of P. citrinum on wound-inoculated fruits. High chitosan-oil concentrations correlated with low disease incidence regardless of storage temperature. Treatments of chitosan-oil coating also inhibited the activity of polyphenol oxidase and maintained vitamin C and phenolic compounds in wounded jujube fruits. Results suggested that the effect of chitosan coating (1.0%) enriched with cinnamon oil (0.75%) on blue mold in jujube fruits may be associated with fungitoxic properties against the pathogen and the elicitation of biochemical defense responses in fruits.

자외선(UV-B)이 봉선화(Impatiens balsamina L.)의 항산화제 및 항산화 효소에 미치는 영향

UV-B 처리가 봉선화 식물에 미치는 영향과 식물의 생화학적 방어반응을 조사하고자 3주간 UV-B (11.34 kJ <TEX>$m^{-2}$</TEX>) 조사 실험을 수행하였다. UV-B 처리에 의해 봉선화의 엽면적 및 건물중이 약 40% 정도 감소하였으며, MDA 함량은 50% 정도 증가한 것으로 나타났다. Glutathione 및 ascorbate acid 함량은 UV-B에 의해 산화형이 증가하고 환원형이 감소하였다. 봉선화 잎에는 주로 3종류의 polyamine이 존재하였으며, 3종류 모두 UV-B에 의해 증가하는 것으로 나타났다. 항산화효소인 SOD, AP, GR 및 GP의 활성이 UV-B 처리에 의해 크게 증가하였다. 이상의 결과로 볼 때 UV-B 증가는 식물체내 산화스트레스를 일으키며, 이에 대해 식물의 생화학적 방어반응이 작용하는 것으로 사료된다. To investigate the effects of ultraviolet(UV-B) on growth and biochemical defense responses of plant, garden balsam (Impatiens balsamina L.) was subjected to enhanced UV-B irradiation [daily dose: 0.02 (No UV-B) and 11.34 (enhanced UV-B) kJ <TEX>$m^{-2}$</TEX> ; <TEX>$UV-B_{BE}$</TEX>] for 3 weeks. Enhanced UV-B drastically inhibited leaf area as well as dry weight of garden balsam. The content of malondialdehyde was significantly increased by about 50% after 3 weeks of UV-B irradiation. The ratios of dehydroascorbate/ascorbate and oxidized glutathione/reduced glutathione were also considerably increased by UV-B irradiation. Three major polyamines of garden balsam leaves: putrescine, spermidine and spermine were observed. All polyamine contents were increased with UV-B irradiation. The enzyme (superoxide dismutase, ascorbate peroxidase etc.) activities of garden balsam were increased by the UV-B enhancement. Based on the results, enhanced UV-B caused oxidative stress in garden balsam and biochemical protection responses might be activated to prevent from damaging effects of oxidative stress generated by UV-B irradiation.

Effects of yeast antagonists in combination with hot water treatment on postharvest diseases of tomato fruit

Hot water treatment (HWT) and two yeast antagonists, Candida guilliermondii and Pichia membranaefaciens were investigated separately and together for controlling Botrytis cinerea, and natural infection in tomato fruit stored at 20 °C. Applied separately, both HWT and antagonists inhibited decay caused by B. cinerea, and natural infection. The combination of antagonists and HWT showed better control efficacy. Application of HWT did not affect the growth of C. guilliermondii and P. membranaefaciens in tomato wounds, while HWT induced significant increase in the activities of phenylalanine ammonia-lyase (PAL), chitinase (CHI) and β-1,3-glucanase in fruit. The mechanism by which HWT enhanced the biocontrol efficacy of the antagonistic yeasts may be related to the elicitation of biochemical defense responses in tomato fruit. The combination of antagonistic yeasts and HWT could be a promising method for the control of postharvest diseases of tomato fruit.

The war of the worlds

The war of the worlds

Control Of Postharvest Decay Of Apple Fruit With Trichoderma Virens Isolates And Induction Of Defense Responses

The biocontrol activity of two isolates of Trichoderma virens against blue mould of apple fruits caused by Penicillium expansum and their ability to induce biochemical defense responses in apple tissue were investigated. Apple fruit (Malus domestica) wounds were inoculated with 20µl antagonist suspension (10 7 conidia/ml) of T. virens and 4 h later with 20 µl of conidial suspension of P. expansum (10 5 conidia/ml). The apples were then incubated at 20°C for 8 days. Lesion diameters were measured 4 and 8 days after inoculation with the pathogen. Two isolates of T. virens were effective in controlling decay of apple fruits caused by P. expansum. Six days after treatment peroxidase activity increased by more than three-fold in apple treated fruit in combination of antagonist and pathogen, in comparison with in wounded, non-inoculated control tissue. Catalase (CAT) activity increased in inoculated fruits in combination of T. virens and P. expansum in comparison with healthy control at all days and maximum activity level was noted at 6 days after inocula- tion. The results indicated that T6 and T8 isolates of T. virens caused the increase in β-1,3-glucanase activity that reached maximum levels 4 and 6 days after inoculation with pathogen, respectively. The increase in β-1,3-glucanase activity was triggered by wounding although the level of increase was markedly lower than detected in treated fruits. Phenolic compounds accumulation showed the highest levels 2-4 days after inoculation and then decreased. The ability of T. virens to increase the activity of peroxidase, catalase, β-1,3-glucanase and levels of phenolic compounds may be one of mechanisms responsible for its biocontrol activity.

표준화 지수를 이용한 환경수목의 오존 내성 결정

수목의 오존 내성을 단기 노출 후 나타난 생리적 피해와 생화학적 반응들의 표준화 지수로 결정하였다. 모감주나무, 벽오동, 때죽나무, 물푸레나무, 백당나무를 150ppb 오존 노출 시킨 후, 광합성 특성, MDA 함량 및 항산화효소의 활성을 측정하여 피해지수는 광합성 파라미터와 MDA 함량 변화를 이용하여 계산하였으며, 내성지수는 항산화효소의 활성 변화를 측정하여 산출하였다. 순양자수율, 탄소고정효율, 광호흡속도는 오존 노출시간에 따라 감소하여, 스트레스 평가지표로 적당한 것으로 판단되었다. 항산화효소의 활성은 수종, 노출시간 및 효소 종류에 따라 다양한 결과를 보여 주었다. 모감주나무 SOD 활성은 오존 노출시간에 따라 증가하였고, 물푸레나무의 SOD 활성은 오존 노출 6 시간 후에 증가하였으며, 벽오동의 CAT 활성은 무처리보다 낮았다. 표준화 지수를 기초로 한 5개 수목의 오존 내성은 두 내성 수종(물푸레나무>모감주나무)과 세 민감성 수종(때죽나무>벽오동>백당나무)으로 구분되었다. Ozone tolerance of tree species was determined by standard index of physiological damages and biochemical defense responses under short-term ozone exposure. At the end of 150ppb <TEX>$O_3$</TEX> fumigation, photosynthetic characteristics and antioxidative enzyme activities were analyzed in the leaves of five species(Koelreuteria paniculata, Firmiana simplex, Styrax japonica, Fraxinus rhynchophylla, Viburnum sargentii). Injury index was determined by the effect of ozone on photosynthetic parameters and malondialdehyde(MDA) content, and tolerance index was calculated using the rate of increase in superoxide dismutase(SOD), ascorbate-peroxidase(APX), glutathione reductase(GR) and catalase(CAT) activities. Apparent quantum yield(AQY), carboxylation efficiency(Ce) and photo-respiration rate(PR) decreased in the leaves of five species with increasing ozone exposure time. These parameters were considered as an appropriate indicator for stress evaluation. Antioxidative enzyme activities showed various results depending on the tree species, exposure time, and enzyme types. SOD activity of K. paniculata increased with ozone exposure time, and that of F. rhynchophylla increased only after 6 hours of ozone exposure. CAT activity of <TEX>$O_3$</TEX>-exposed F. simplex was lower than the control. Based on standard index, ozone tolerance ability of five species was determined as two tolerant species(F. rhynchophylla > K. paniculata) and three sensitive species(S. japonica > F. simplex > V. sargentii).

Effect of salicylic acid on the activities of anti-oxidant enzymes and phenylalanine ammonia-lyase in cucumber fruit in relation to chilling injury

SummaryThe effect of salicylic acid (SA) on chilling injury (CI) in cucumber fruit, and its ability to induce biochemical defense responses were assessed. To explore the optimum concentration of SA to induce chilling tolerance, cucumber fruit were treated with 0.1, 0.5, or 1.0 mM SA then stored for 18 d at 1°C. The results showed that the application of SA at 0.5 mM was most effective in reducing CI in cucumber fruit. SA at 0.5 mM maintained significantly higher fruit firmness and a lower CI index and malondialdehyde (MDA) content compared with untreated controls. Meanwhile, treatment with 0.5 mM SA delayed decreases in skin chlorophyll and vitamin C contents. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and phenylalanine ammonia-lyase (PAL) were increased in SA-pretreated cucumbers stored under chilling stress. These results suggested that pre-treatment with 0.5 mM SA could alleviate CI symptoms effectively and maintain fruit quality in cucumber. The enhanced chilling tolerance of cucumber fruit was due mainly to the increased activities of the anti-oxidant enzymes and PAL induced by SA. Post-harvest application of SA could be used commercially to control CI in cucumber fruit during cold storage.

Potential of the biopolymer chitosan with different molecular weights to control postharvest gray mold of tomato fruit

Gray mold caused by Botrytis cinerea (Pers.) is the most economically important postharvest disease of fruit and vegetables at harvest and during storage. Therefore the current study was conducted to investigate the effectiveness of chitosan with different molecular weights on gray mold in vitro and in vivo in tomato fruit ( Solanum lycopersicum L. var. lycopersicum) stored at different temperatures. In an in vitro experiment, the results demonstrated that the antifungal activity increased as the chitosan molecular weight decreased. In an in vivo study, chitosan treatments significantly reduced fungal decay and all compounds with concentrations of 2000 and 4000 mg/L showed complete control of the fungus in wound-inoculated fruit. Chitosan with a molecular weight of 5.7 × 10 4 g/mol was the most effective compound among those tested. The results also revealed that high chitosan concentrations correlated with low disease incidence regardless of storage conditions. In addition to the antifungal activity, chitosan had the potential for the elicitation of defense markers, including total soluble phenolic compounds, polyphenoloxidase (PPO) activity and total protein content. Chitosan treatment decreased the activity of PPO and enhanced total protein and phenolic compounds in wounded tomato fruit. These findings suggest that the effects of chitosan with different molecular weights on gray mold in tomato fruit may be associated with direct fungitoxic properties against the pathogen, and the elicitation of biochemical defense responses in fruit.

Effect of Pichia membranaefaciens combined with salicylic acid on controlling brown rot in peach fruit and the mechanisms involved

AbstractBACKGROUND: Fruits are usually stored at low temperature to slow physiological metabolism, maintain quality and extend storage life. However, brown rot caused by Monilinia fructicola often occurs in peach fruit at low temperature, resulting in serious losses. As a promising alternative to the use of synthetic fungicides, the antagonistic yeast Pichia membranaefaciens showed a potential effect on controlling post‐harvest brown rot. To improve biocontrol efficacy of the yeast against fungal pathogen, the biocontrol efficacy of P. membranaefaciens combined with salicylic acid (SA) in inhibiting brown rot in peach fruit caused by M. fructicola was investigated.RESULTS: As compared to P. membranaefaciens used alone, the yeast combined with SA significantly reduced lesion diameter caused by M. fructicola, and increased the activities of chitinase, β‐1,3‐glucanase and peroxidase (POD), as well as enhanced the expressions of chitinase and β‐1,3‐glucanase genes in peach fruit. Moreover, SA at 2 mmol concentration did not affect yeast growth, but inhibited pathogen growth.CONCLUSION: The mechanism by which SA enhances the biocontrol efficacy of the antagonistic yeast against brown rot may be related to inducing biochemical defence responses in peach fruit, and a moderate inhibitory effect of SA on growth of M. fructicola. Copyright © 2008 Society of Chemical Industry

Effects of chitosan on control of postharvest diseases and physiological responses of tomato fruit

The effects of chitosan on gray mould and blue mould caused by Botrytis cinerea and Penicillium expansum in tomato fruit stored at 25 and 2 °C, respectively, were investigated. Chitosan provided an effective control of both diseases of tomato fruit stored at 25 and 2 °C. Chitosan strongly inhibited spore germination, germ tube elongation, and mycelial growth of B. cinerea and P. expansum in vitro, and damaged the plasma membranes of spores of both pathogens. Chitosan treatment induced a significant increase in the activities of polyphenoloxidase (PPO), peroxidase (POD), and enhanced the content of phenolic compounds in tomato fruit. These findings suggest that the effects of chitosan on gray mould and blue mould in tomato fruit may be associated with the direct fungitoxic property against the pathogens, and the elicitation of biochemical defense responses in fruit.

Nonenzymatic lipid peroxidation reprograms gene expression and activates defense markers in Arabidopsis tocopherol-deficient mutants.

Tocopherols (vitamin E) are lipophilic antioxidants that are synthesized by all plants and are particularly abundant in seeds. Two tocopherol-deficient mutant loci in Arabidopsis thaliana were used to examine the functions of tocopherols in seedlings: vitamin e1 (vte1), which accumulates the pathway intermediate 2,3-dimethyl-5-phytyl-1,4-benzoquinone (DMPBQ); and vte2, which lacks all tocopherols and pathway intermediates. Only vte2 displayed severe seedling growth defects, which corresponded with massively increased levels of the major classes of nonenzymatic lipid peroxidation products: hydroxy fatty acids, malondialdehyde, and phytoprostanes. In the absence of pathogens, the phytoalexin camalexin accumulated in vte2 seedlings to levels 100-fold higher than in wild-type or vte1 seedlings. Similarly, gene expression profiling in wild-type, vte1, and vte2 seedlings indicated that increased levels of nonenzymatic lipid peroxidation in vte2 corresponded to increased expression of many defense-related genes, which were not induced in vte1. Both biochemical and transcriptional analyses of vte2 seedlings indicate that nonenzymatic lipid peroxidation plays a significant role in modulating plant defense responses. Together, these results establish that tocopherols in wild-type plants or DMPBQ in vte1 plants limit nonenzymatic lipid peroxidation during germination and early seedling development, thereby preventing the inappropriate activation of transcriptional and biochemical defense responses.

UV-B가 강낭콩(Phaseolus vulgaris L.)의 지방산 구성, 지질과산화 및 polyamine 함량에 미치는 영향

UV-B에 의한 강낭콩 식물의 피해양상, 지질과산화, 지질조성 변화와 UV-B에 대한 식물의 방어기작 등을 조사하기 위하여 3주간 UV-B 조사 실험을 수행하였다. UV-B 처리에 의해 초장이 약 22% 정도 감소하는 것으로 나타났다. MDA 함량은 UV-B 처리에 의해 약 50% 정도 증가하는 것으로 나타났다. Glutathione 및 ascorbate acid 함량은 UV-B 조사에 의해 산화형이 증가하고 환원형이 감소하는 것으로 나타났다. UV-B 조사에 의한 지방산 구성 변화를 조사한 결과 당지질 및 인지질 모두 UV-B조사에 의해 포화지방산이 증가하는 것에 반해, 불포화지방산이 감소하는 것으로 나타났다. 강낭콩 잎에는 주로 3종류의 polyamine이 존재하는 것으로 나타났으며, 3종류 모두 UV-B 조사에 의해 증가하는 것으로 나타났다. 본 실험 결과로 볼 때, UV-B 조사는 활성산소를 생성하여 생체막 지질에 직접적인 영향을 미치는 것으로 나타났으며, ascorbate acid, glutathione, polyamine 등의 항산화물질들이 이에 대한 피해를 최소화하기 위하여 작용하는 것으로 나타났다. To investigate the effects of UV-B on fatty acid composition, lipid peroxidation and biochemical defense responses of plant, kidney bean (Phaseolus vulgaris L.) was subjected to enhanced UV-B irradiation [daily dose : 0.02.(No UV-B) and 11.36 (enhanced UV-B) <TEX>$kJ\;m^{-2};UV-B_{BE}$</TEX>] for 3 weeks. UV-B drastically inhibited both height and dry weight of kidney bean. The content of malondialdehyde significantly increased by about 50% after 3 weeks of UV-B irradiation. The ratio of unsaturated to saturated fatty acids of kidney bean was increased by UV-B irradiation. Three major polyamines of kidney bean leaves : putrescine, spermidine and spermine, were observed. All of the polyamine contents were increased with UV-B irradiation. These results suggested that enhanced UV-B radiation caused oxidative stress on lipids and biochemical protection responses might be activated to prevent from damaging effects of oxidative stress generated by UV-B irradiation.

봉선화(Impatiens balsamina L.)에 대한 pH 수준별 처리가 항산화 물질 및 관련 효소 활성에 미치는 영향

To investigate the effects of simulated acid rain (SAR) on growth and biochemical defense responses of plant, garden balsam (Impatiens balsamina L.) was subjected to four levels of SAR based on pH (5.6, 4.0, 3.0, 2.0) and placed in the growth chambers for 2 weeks. SAR drastically inhibited both height and dry weight of garden balsam. The content of total carotenoid was tended to decrease, but the level of malondialdehyde was significantly increased by SAR. As the pH levels decreased from 5.6 to 2.0, the content of dehydroascorbate and oxidized glutathione of the plant were significantly increased. The enzyme (superoxide dismutase, ascorbate peroxidase etc.) activities of the plant affected by SAR were increased as the pH decreased. The results indicate that garden balsam may receive oxidative stresses by the application of SAR and by which the plant growth can be significantly retarded. A biochemical protective mechanism might be activated to nullify the oxidative stresses generated through SAR.

Enhancement of Biocontrol Activity of Cryptococcus laurentii by Silicon and the Possible Mechanisms Involved

ABSTRACT Exogenous application of silicon (Si) in the form of sodium metasilicate reduced disease development caused by Penicillium expansum and Monilinia fructicola in sweet cherry fruit at 20 degrees C. The inhibition of fruit decay was correlated closely with Si concentrations. Silicon at concentrations of 1%, in combination with the biocontrol agent Cryptococcus laurentii at 1 x 10(7) cells per ml, provided synergistic effects against both diseases. Population dynamics of C. laurentii were stimulated by Si 48 h after the yeast treatment in the wounds of sweet cherry fruit. Silicon strongly inhibited spore germination and germ tube elongation of P. expansum and M. fructicola in vitro. Based on results with scanning electron microscopy, growth of both pathogens was significantly inhibited by Si in the wounds of sweet cherry fruit. Compared with the wounded water control, Si treatment induced a significant increase in the activities of phenylalanine ammonia-lyase, polyphenoloxidase, and peroxidase in sweet cherry fruit but did not increase the levels of lignin. Application of Si activated a cytochemical reaction and caused tissue browning near the site of wounding. Based on our studies, the improvement in biocontrol efficacy of antagonistic yeast when combined with Si may be associated with the increased population density of antagonistic yeast by Si, the direct fungitoxicity property of Si to the pathogens, and the elicitation of biochemical defense responses in fruit.

Expression proteomics identifies biochemical adaptations and defense responses in transgenic plants with perturbed polyamine metabolism

Soluble proteins from leaves of transgenic tobacco plants with perturbed polyamine metabolism, caused by S-adenosylmethionine decarboxylase overexpression, were analysed by comparative proteomics. A group of proteins was found to be increasingly repressed, in parallel with the degree of polyamine perturbation, in each of the three independent transgenic lines. These were identified as isoforms of chloroplast ribonucleoproteins, known to be involved in chloroplast mRNA stability, processing and translation. Another group of eight proteins strongly induced in the most metabolically perturbed line was identified as multiple, uncharacterised isoforms of the defense protein PR-1, a known marker for systemic acquired resistance.

Functional characterization of nine Norway Spruce TPS genes and evolution of gymnosperm terpene synthases of the TPS-d subfamily.

Constitutive and induced terpenoids are important defense compounds for many plants against potential herbivores and pathogens. In Norway spruce (Picea abies L. Karst), treatment with methyl jasmonate induces complex chemical and biochemical terpenoid defense responses associated with traumatic resin duct development in stems and volatile terpenoid emissions in needles. The cloning of (+)-3-carene synthase was the first step in characterizing this system at the molecular genetic level. Here we report the isolation and functional characterization of nine additional terpene synthase (TPS) cDNAs from Norway spruce. These cDNAs encode four monoterpene synthases, myrcene synthase, (-)-limonene synthase, (-)-alpha/beta-pinene synthase, and (-)-linalool synthase; three sesquiterpene synthases, longifolene synthase, E,E-alpha-farnesene synthase, and E-alpha-bisabolene synthase; and two diterpene synthases, isopimara-7,15-diene synthase and levopimaradiene/abietadiene synthase, each with a unique product profile. To our knowledge, genes encoding isopimara-7,15-diene synthase and longifolene synthase have not been previously described, and this linalool synthase is the first described from a gymnosperm. These functionally diverse TPS account for much of the structural diversity of constitutive and methyl jasmonate-induced terpenoids in foliage, xylem, bark, and volatile emissions from needles of Norway spruce. Phylogenetic analyses based on the inclusion of these TPS into the TPS-d subfamily revealed that functional specialization of conifer TPS occurred before speciation of Pinaceae. Furthermore, based on TPS enclaves created by distinct branching patterns, the TPS-d subfamily is divided into three groups according to sequence similarities and functional assessment. Similarities of TPS evolution in angiosperms and modeling of TPS protein structures are discussed.

Induction of Chitinase, β-1,3-Glucanase, and Phenylalanine Ammonia Lyase in Peach Fruit by UV-C Treatment

ABSTRACT Treatment of peach fruit with UV-C light caused a rapid induction of chitinase, beta-1,3-glucanase, and phenylalanine ammonia lyase (PAL) activities starting 6 h after treatment and reaching maximum levels at 96 h after treatment. By 96 h after UV-C treatment, chitinase, beta-1,3-glucanase, and PAL activities in UV-C-treated fruit were over twofold above the levels observed for the control. In nontreated control fruit, no apparent increase in chitinase and beta-1,3-glucanase activities was detected but a minor increase in PAL activity was seen. The transient increase in chitinase, beta-1,3-glucanase, and PAL activities in UV-C-treated fruit was preceded by a gradual activation of the corresponding genes. UV-C-treated fruit showed an increase in accumulation of beta-1,3-glucanase and chitinase mRNAs at 3 h after treatment, which peaked approximately 96 h posttreatment. A similar induction kinetic pattern was observed for PAL mRNA in response to UV-C treatment, except the induction started 6 h after UV-C treatment. These results show that the response of peach fruit to elicitor treatment is similar to that seen in other plant-elicitors interactions and suggests the involvement of peach biochemical defense responses in UV-C-mediated disease resistance.

Enhancement of biocontrol efficacy of antagonistic yeasts by salicylic acid in sweet cherry fruit

Salicylic acid (SA) and two yeast antagonists, Rhodotorula glutinis and Cryptococcus laurentii, were investigated separately and together for controlling Penicillium expansum and Alternaria alternata in sweet cherry fruit. Applied separately, both SA (0·5 m m, pH 3·6) and antagonists inhibited decay caused by P. expansum and A. alternata. Biocontrol activity of R. glutinis was enhanced in combination with SA, whereas the efficacy of C. laurentii was not affected. Application of SA did not affect the growth of R. glutinis and C. laurentii in cherry wounds. Results of in vitro studies showed that SA at low concentrations had little effect on the growth of the yeasts or the pathogens. SA treatment induced a significant increase in polyphenoloxidase, phenylalanine ammonia-lyase, and β-1,3-glucanase activity in cherry fruit, but did not alter the levels of peroxidase. The mechanism by which SA enhanced the biocontrol efficacy of the antagonistic yeast may be related to its ability to induce biochemical defense responses in sweet cherry fruit rather than its fungitoxicity effects on the pathogens.

Seed Treatment of Barley with Idriella bolleyi causes Systemically Enhanced Defence against Root and Leaf Infection by Bipolaris sorokiniana

Inoculation of barley seed with the saprophytic fungus Idriella bolleyi caused systemically improved resistance on both leaves and roots of young plants to subsequent infection with the necrotrophic fungus Bipolaris sorokiniana . Lesion sizes were reduced by up to 50% as a result of the seed treatment. Seed and root inoculation with I. bolleyi induced biochemical defence responses in the plants as shown by slight accumulation of pathogenesis-related (PR) proteins, but the accumulation was not as great as when the roots were inoculated with B. sorokinina . Conidia of I. bolleyi applied to seed survived well during storage, with no significant reduction in colony forming units (CFUs) occurring at 15°C after 2 months. However, storage at 28°C decreased the viability of the applied conidia. The fungus colonized the seed and roots during field conditions as indicated by high numbers of CFUs. Two months after sowing, frequencies of I. bolleyi were higher on plants treated with the fungus than on control plants where colonization occurred naturally from field soil. The implications of the results are discussed in relation to earlier reports of biological control of cereal root diseases by I. bolleyi and induced resistance.