Search

Plants resist pathogen attack through a combination of constitutive and inducible defences. Different types of induced resistance have been defined based on differences in signalling pathways and spectra of effectiveness. Systemic acquired resistance (SAR) occurs in distal plant parts following localized infection by a necrotizing pathogen. It is controlled by a signalling pathway that depends upon the accumulation of salicylic acid (SA) and the regulatory protein NPR1. In contrast, induced systemic resistance (ISR) is promoted by selected strains of non-pathogenic plant growth-promoting rhizobacteria (PGPR). ISR functions independently of SA, but requires NPR1 and is regulated by jasmonic acid (JA) and ethylene (ET).Resistance can be induced by treatment with a variety of biotic and abiotic inducers. The resistance induced is broad spectrum and can be long-lasting, but is rarely complete, with most inducing agents providing between 0·20 and 0·85 disease control. In the field, expression of induced resistance is likely to be influenced by the environment, genotype, crop nutrition and the extent to which plants are already induced. Unfortunately, understanding of the impact of these influences on the expression of induced resistance is rudimentary. So too is understanding of how best to use induced resistance in practical crop protection. This situation will need to change if induced resistance is to fulfil its potential in crop protection. [ABSTRACT FROM PUBLISHER]

The relationship between yield loss and disease severity can differ widely between crops. This has given rise to the concept of disease tolerance, with some crops exhibiting a smaller yield loss under a given severity of disease than others. Genetic improvement to minimise yield loss under disease is an attractive goal, as it exerts little or no selection pressure on pathogen populations, and could form a useful component of durable disease management programmes. However, progress towards this end requires a thorough understanding of the phenotypic traits that influence the response of yield to disease, their genetic control and the possible trade-offs involved with other desirable agronomic characteristics. This paper examines the candidate crop traits that may confer tolerance of foliar disease in wheat and barley and reviews evidence of genetic variation in their expression. In wheat grown under the relatively low light conditions of North-West Europe, post-anthesis source (assimilate supply) and grain sink capacity (capacity for dry matter accumulation) appear to be closely balanced. Traits associated with maintaining post-anthesis radiation interception and radiation use efficiency in spite of disease may confer tolerance. The most promising traits include a larger flag leaf and compensatory increases in photosynthetic rate in non-infected parts of leaves. In barley, yield is often more strongly sink limited, and early-season disease management is required to protect the formation of potential grain sites. A wider range of potential traits may influence tolerance including compensatory adjustments in leaf growth and morphology, and differences in the sensitivity of tiller and spikelet mortality to photoassimilate supply. Different methods for quantifying tolerance are suggested depending on the trait of interest. [ABSTRACT FROM AUTHOR]

A great deal of information is available in the literature on the effects of nutrition on disease development in plants and crops. However, much of this information is contradictory and although it is widely recognised that nutrition can influence disease in crops, limited progress has been made in the manipulation of crop nutrition to enhance disease control. Achieving this aim requires a sound understanding of the effects of fertilisation on nutrient levels and availability in crop tissues, and in turn, how the nutrient status of such tissues influences pathogen infection, colonisation and sporulation. Some of these details are known for a number of crop plants under controlled conditions, but very little of this type of information is available for crops under field conditions. This review focuses on nitrogen, sulphur, phosphorus, potassium and silicon, examines the availability of these nutrients in plant tissues to support pathogen growth and development, and reviews the effects of the different nutrients on disease development. The review also examines the potential for manipulating crop nutrition to enhance disease control in conventional and organic cropping systems. [ABSTRACT FROM AUTHOR]

The antifungal and fungicidal effects of two chemotypes of basil (Ocimum basilicum) oil and its major individual components were studied in a series ofin vitroandin vivoexperiments. Mycelial growth of the plant pathogenic fungusBotrytis fabaewas reduced significantly by both the methyl chavicol chemotype oil and the linalol chemotype oil, and the major individual components of the oils all reduced fungal growth, with methyl chavicol, linalol, eugenol and eucalyptol reducing growth significantly. Combining the pure oil components in the same proportions as found in the whole oil led to very similar reductions in fungal growth, suggesting that the antifungal effects of the whole oils were due primarily to the major components. When the fungus was exposed to the oils in liquid culture, growth was reduced by concentrations considerably smaller than those used in the Petri dish studies.Botrytis fabaeand the rust fungusUromyces fabaewere also controlledin vivo, with the whole oils of both chemotypes, as well as pure methyl chavicol and linalol, reducing infection of broad bean leaves significantly. Most effective control of fungal infection was achieved if the treatments were applied 3 h postinoculation. [ABSTRACT FROM AUTHOR]

Abstract In the incompatible interaction between the barley cultivar Hart (mlo allele) and the powdery mildew fungus Blumeria graminis DC. Speer f. sp. hordei Marchal, free spermidine and conjugated forms of putrescine and spermidine were found to accumulate 1–3 days following inoculation. The increase in free spermidine could be accounted for by increased activities of the biosynthetic enzymes ornithine decarboxylase (EC 4.1.1.17) and S-adenosylmethionine decarboxylase (EC 4.1.1.50). Activities of the transferase enzymes putrescine hydroxycinnamoyl transferase (EC 2.3.1.-) and tyramine feruloyl-CoA transferase (EC 2.3.1.-) were also increased in leaves of Hart inoculated with powdery mildew, as were activities of the polyamine catabolic enzymes diamine oxidase (DAO, EC 1.4.3.6) and polyamine oxidase (PAO, EC 1.4.3.4). The possible role of conjugated polyamines, and increases in DAO and PAO, in penetration based resistance to powdery mildew infection is discussed. [ABSTRACT FROM AUTHOR]

Abstract Polyamine levels and activities of enzymes of polyamine biosynthesis and catabolism were examined in the barley cultivar Delibes (Ml1al + Ml(Ab) ) reacting hypersensitively to the powdery mildew fungus, Blumeria graminis f. sp. hordei (race CC220). Levels of free putrescine and spermine and of conjugated forms of putrescine, spermidine and spermine were greatly increased 1–4 d following inoculation of barley with the powdery mildew. These changes in polyamine levels were accompanied by elevated activities of the polyamine biosynthetic enzymes ornithine decarboxylase (ODC), arginine decarboxylase (ADC) and S -adenosylmethionine decarboxylase (AdoMetDC) and the polyamine catabolic enzymes diamine oxidase (DAO) and polyamine oxidase (PAO). Activities of two enzymes involved in conjugating polyamines to hydroxycinnamic acids, putrescine hydroxycinnamoyl transferase (PHT) and tyramine feruloyl-CoA transferase (TFT) were also examined and were found to increase significantly 1–4 d after inoculation. The possibility that the increased levels of free spermine, increased polyamine conjugates, and increased DAO and PAO activities are involved in development of the hypersensitive response of Delibes to powdery mildew infection is discussed. [ABSTRACT FROM AUTHOR]

The antifungal and fungicidal effects of hyssop (Hyssopus officinalis) oil and its individual components were studied in a series of in vitro and in vivo experiments. Mycelial growth of the plant pathogenic fungi Pyrenophora avenae and Pyricularia oryzae was completely inhibited by 0.4% hyssop oil. Volatile components diffusing from agar medium containing 0.4% hyssop oil also completely inhibited the growth of these two fungi. Various components of hyssop oil (L-bornyl acetate, isopinocampheol and pinocamphone), used individually, reduced growth of P. avenae and, where combinations of individual components were used, any mixture containing isopinocampheol completely inhibited fungal growth. Growth of P. oryzae was less affected by individual components of the oil. Hyssop oil reduced germination of Botrytis fabae conidia and uredospores of Uromyces viciae-fabae, but in contrast to the data from in vitro experiments, its effects on pathogen infection were less clear cut. Thus, although 0.05% hyssop oil reduced rust infection of broad bean when applied 1, 2 or 3 days before, or 1 or 2 days after inoculation, its effects against barley powdery mildew and apple powdery mildew were variable. It is suggested that this variability might be the result of the volatile components of the oil diffusing away from leaf surfaces, thus reducing the concentration of active components on the leaf surface. [ABSTRACT FROM AUTHOR]

Ethokem (Midkem Agrochemicals, Northampton, UK) and Bond (Newman Agrochemicals, Cambridge, UK) completely inhibited linear growth of Pyricularia oryzae at 1 and 2% concentrations of the compounds and strongly inhibited growth of Pyrenophora avenae in vitro. Vapor Gard (Miller Chemical & Fertilizer Corporation, Hannover, PA, USA) was less effective with relatively little inhibition of P. oryzae, but was a more effective inhibitor of P. avenae. All three compounds decreased cell lengths of both pathogens and increased cell diameters of P. avenae. Vapor Gard and Ethokem did not significantly alter cell diameters of P. oryzae, but a highly significant increase was observed with Bond. Gross changes in hyphal morphology were observed including swollen shortened cells, granulation of the cytoplasm, increased branching and collapsed empty cells. Ethokem and Bond decreased growth rate and inhibited biomass production of P. avenae. [ABSTRACT FROM AUTHOR]

The spermidine synthase inhibitor cyclohexylamine (CHA) and the spermidine analogue norspermidine were evaluated against powdery mildew infection of spring barley in field trials over a 2-year period. Both compounds reduced mildew infection as effectively as a commercial fungicide, a mixture of flutriafol and carbendazim. Percentage disease reduction afforded by CHA and norspermidine in year 1 ranged from 32% to 67% at the final assessment and from 52% to 77% in year 2 of the study, when compared with plants from untreated plots. No difference was observed in the disease control conferred by 1.0 mM concentrations of the compounds and 5.0 mM applications, the optimum dose being less than 5.0 mM. No significant differences in final yield were obtained, comparing the treated crop with the untreated control. Although reductions in disease were apparent, additional environmental factors may have prevented a subsequent crop yield response. [ABSTRACT FROM AUTHOR]

Effects were examined of barley powdery mildew (Erysiphe graminis f. sp. bordei) the major leaf protein, ribulose-1,5-bisphosphate carboxylase (RuBPCase), and other enzymes of CO2 assimilation, phosphoenolpyruvate carboxylase (PEPcase), and malic enzymes, and enzymes associated with RuBPCase in the reductive pentose phosphate pathway. Activity of RuBPCase per unit fresh weight of leaf was inhibited by infection from the first sample, 3 days after inoculation, to the last sample, 24 days after inoculation, when healthy control leaves were visibly senescing. The inhibition occurred because the amount of RuBPCase protein (measured specifically by an immunological technique) was reduced from 6 days after inoculation, at which time there was little protein remaining. Activity of PEPcase per unit fresh weight of leaf was initially stimulated by infection, but, thereafter, it was inhibited. Inhibition, like that also affecting malic enzymes (NAD) and (NADP), 3-phosphglycerate kinase, and glyceraldehydes-3-phosphate dehyrogenases (NAD) and (NADP), was associated with a decline in amounts of total soluble minus RuBPCase protein per unit fresh weight of leaf. Reduced amounts of leaf protein may be associated with reduced nitrate uptake by roots and fungal demand for nitrogen in mildewed plants. [ABSTRACT FROM AUTHOR]

The diamine putrescine and the polyamines spermidine and spermine are ubiquitous in nature and are essential for cell proliferation. Since polyamine biosynthesis in plants can start from either ornithine or arginine, while fungal polyamine biosynthesis appears to utilise only the ornithine route, it was suggested that specific inhibition of fungal polyamine biosynthesis should be lethal. Indeed, inhibitors of polyamine biosynthesis, e.g. the ornithine decarboxylase inhibitor α-difluoromethylornithine, have been shown to inhibit fungal growth in vitro and to control fungal infections on a variety of plants under glasshouse and field conditions. It is now known that polyamine analogues can perturb polyamine metabolism leading to powerful antiproliferative effects in cancer cells. This paper reviews the results of a research programme focused on the synthesis and evaluation of putrescine analogues as novel fungicides. A number of aliphatic, alicyclic and cyclic diamines have been shown to possess considerable fungicidal activity, but although many of these compounds perturb polyamine metabolism in fungal cells, such changes are not considered sufficient to account for the observed antifungal effects. More recent work on spermidine analogues is also described. [ABSTRACT FROM AUTHOR]

First leaves of barley seedlings grown in solution culture were inoculated with powdery mildew when the second leaf was fully emerged. 14C-labelled carbon dioxide was fed to either first or second leaves of infected and non-infected plants. Translocation of labelled photoassimilates into roots, and partitioning into soluble, storage and structural fractions were studied in tip, mid and basal regions of primary roots 24 h after feeding. Mildew reduced the total activity in the plant, but had little effect on assimilate distribution since the percentage activity translocated to roots was only transiently reduced, approximately 7 days after infection. Reduced import led to a reduction in the specific activity of different fractions within roots, reductions being greatest in root tips. These changes were similar whichever leaf was fed. Changes in specific activity became progressively more pronounced in the 10 days following infection, and were paralleled by a reduction in the mitotic index of root tips. It is concluded that meristematic activity, and thus the growth, of primary roots of barley is particularly sensitive to reductions in photoassimilation caused by powdery mildew infection. [ABSTRACT FROM AUTHOR]

Mycelial growth, polyamine concentrations and the activities of enzymes of polyamine biosynthesis and catabolism were examined in Phytophthora infestans and Pythium ultimum grown in the presence of difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), and difluoromethylarginine (DFMA), an inhibitor of arginine decarboxylase (ADC). Growth of P. infestans was reduced by DFMO and a mixture of DFMO + DFMA, but was increased by DFMA at concentrations of 5mM and greater. Polyamine concentrations and ODC activity were significantly reduced in P. infestans grown on all inhibitor treatments. In contrast, growth, polyamine concentrations and enzyme activities were not affected in P. ultimum exposed to the inhibitors. It seems unlikely that P. infestans and P. ultimum possess ADC activity, as neither of the products of ADC activity (agmatine and putrescine) could be detected in ADC assays. Although ODC from P. infestans was sensitive to DFMO, ODC from P. ultimum was insensitive to the inhibitor. Moreover, uptake of DFMO by P. infestans was three times greater than that observed by P. ultimum. [ABSTRACT FROM AUTHOR]

Resistance in the upper leaves of broad bean (Vicia faba) plants to infection by the rust fungus, Uromyces viciae-fabae, was increased following treatment of the lower leaves with 10 mM potassium phosphate or 5 mM EDTA. Increasing the interval between treatment of the lower leaves and inoculation of the upper leaves had little effect on rust infection. Thus rust infection was reduced by 50 and 34% if the upper leaves were inoculated 1 day after treatment of the lower leaves with potassium phosphate or EDTA, respectively, while there was a 75% reduction in infection if the interval between treatment and inoculation was increased to 12 days. Application of calcium nitrate (10 mM) after the phosphate or EDTA treatments prevented the induction of systemic resistance. Calcium nitrate applied alone to the lower leaves had no significant effect on rust infection of the upper leaves. [ABSTRACT FROM AUTHOR]

The concentrations of three amines (putrescine, spermidine and spermine) were much increased in first leaves of barley infected with powdery mildew, whilst the concentrations of putrescine and spermidine in roots of mildewed barley were significantly decreased. Although no significant change in the activities of three polyamine biosynthetic enzymes (ADC, arginine decarboxylase; ODC, ornithine decarboxylase; and SAMDC, S-adenosyl methionine decarboxylase) could be detected in roots of mildewed barley, the activities of ADC, ODC and SAMDC were increased in infected first leaves. The significance of these alterations in polyamines and their biosynthetic enzymes in mildewed barley is discussed. [ABSTRACT FROM AUTHOR]

The paper reports a programme of international co-operation in occupational hygiene education and training. Through a number of initiatives the European Commission encourages exchanges within higher education and between higher education and industry across member states. The present programme was initiated through involvement with one of these schemes, namely ERASMUS. Although occupational health and safety is a very small part of higher education, as a subject it does pose a number of interesting problems for the European Community. Furthermore, the European dimension of occupational health is something that those involved in the profession cannot afford to ignore. The implication of directives, the harmonization of standards, the comparability of regulation, control and professional practice are all issues that are raised in such a cross-European programme. The paper specifically reports the results of five comprehensive occupational hygiene surveys carried out with the co-operation of major Greek industries. Although the findings of the surveys are themselves interesting and are discussed in the text, the main aim of the paper is to place the findings within the context of the European development of higher education and training in occupational health and safety, and to comment on a number of issues that emerged during the work that are relevant to the wider European perspective. [ABSTRACT FROM PUBLISHER]

Abstract This study aimed at examining the effects of the saturated fatty acid lauric acid on mycelial growth of Rhizoctonia solani and Pythium ultimum and on infection of barley seedlings with Blumeria graminis f. sp. hordei . Mycelial growth of R. solani and P. ultimum in agar culture was significantly reduced by lauric acid at concentrations of 100 μm and above, while no fungal growth occurred in liquid culture at concentrations above 50 μm. Application of lauric acid at concentrations ranging from 250 to 1000 μm to barley leaves before or after inoculation with B. graminis f. sp. hordei led to significant reductions in infection. This study provides the first report of the activity of lauric acid against plant pathogenic fungi and indicates the need for investigation of its mechanism of action. [ABSTRACT FROM AUTHOR]

The kinetics of glutamic acid and glutamine uptake in the light leaf spot fungus, Pyrenopeziza brassicae, are biphasic. At low and high concentrations, glutamic acid and glutamine share a high-affinity and a low-affinity carrier, respectively, with KmS of 4.0 and 4.4μM for uptake of glutamic acid and glutamine, respectively, by the high-affinity system, and KmS of 580 and 560 μM for uptake of glutamic acid and glutamine by the low-affinity system. The data suggest that glutamic acid and glutamine are taken up by a different system to that responsible for the uptake of ornithine, arginine, lysine and asparagine, and may represent system IV described in Neurospora crassa for the uptake of acidic amino acids. [ABSTRACT FROM AUTHOR]

Six novel N,N-dialkyl derivatives of spermidine were synthesised and examined for activity against the oat stripe pathogen Pyrenophora avenae. Two of these spermidine analogues, N,N-dimethyl-N1-(3-aminopropyl)-1,3-diaminopropane trihydrochloride (27) and N,N-dimethyl-N1-(3-aminopropyl)-1,4-diaminobutane trihydrochloride (28), reduced radial extension of P. avenae on plates when used at 2 mM, and caused more substantial reductions in fungal growth in liquid culture when used at 1 mM. Preliminary data suggest that neither compound affected polyamine biosynthesis, determined by following the incorporation of label from ornithine into polyamines and examining intracellular polyamine concentrations in fungal tissue.

Biomass production by Aspergillus fumigatus was greatest at 40-45 degrees C and was associated with an increase in concentration of the diamine putrescine and activity of its biosynthetic enzyme ornithine decarboxylase. Concentrations of the other amines, cadaverine, spermidine and spermine were considerably lower than putrescine concentration and did not change significantly over the temperature range 20-50 degrees C. This is surprising in view of the greatly increased flux of label from ornithine through to spermidine at 45 and 50 degrees C, indicating an increased formation of this triamine. It is suggested that there was increased formation of spermidine derivatives at these temperatures. Interestingly, there was greatly increased formation of the higher homologues of cadaverine, aminopropylcadaverine and N,N'-bis(3-aminopropyl)cadaverine, in A. fumigatus at 45 and 50 degrees C.