Does nitrogen fertilization have an impact on the trade-off between willow growth and defensive secondary metabolism?

The effect of nitrogen fertilization on the phytomass production, shoot length and leaf secondary phenolics in nine Salix myrsinifolia clones was investigated. Cuttings taken from 1-year-old and 2-year-old shoot parts of field cultivated clones were grown at three concentrations of nitrogen (7, 150 and 300 ppm) in a greenhouse for one growing season. The willow clones differed significantly in phytomass yield and secondary phenolics content. Nitrogen fertilization affected significantly the growth and secondary metabolism of willow clones. In most clones, the addition of nitrogen from a sub-optimum concentration (7 ppm) to an optimum concentration (150 ppm) appeared to reduce the amounts of salicortin, chlorogenic acid and unknown salicylate and increased shoot phytomass, but a supraoptimum nitrogen concentration (300 ppm) resulted in highly variable growth and secondary phenolic responses. A significantly negative correlation between leaf phytomass and amount of total phenolics at sub-optimum and optimum N-treatments indicates trade-off between growth and secondary metabolism in willow clones at these treatments. However, the leaf phytomass:total amount of phenolics ratio varied significantly among clones, and in all clones it was not significantly lower at sub-optimum N-treatment than at optimum N-treatment.     

Herbivores and pathogens on willow: do they affect each other?

Abstract 1 Willows often need to cope with attack by both rust fungi and herbivores. We studied whether rust infection on willow affects the herbivore, and vice versa, whether herbivore feeding affects the fungal infection. The system investigated by laboratory bioassays and greenhouse experiments consisted of the willow hybrid Salix × cuspidata, the rust Melampsora allii‐fragilis and the willow leaf beetle Plagiodera versicolora. Effects were studied both on a local scale (rust infection and feeding on the same leaf) and systemically (rust infection and feeding on different, but adjacent leaves). 2 Rust infection was not affected by herbivore feeding on a local scale. Systemically, however, the willow's susceptibility towards rust infection was increased by herbivore feeding, as indicated by a higher number of rust sori on leaves adjacent to feeding‐damaged leaves. The herbivore's performance was detrimentally affected by rust infection: increase of mortality (systemically), decrease of larval weight (locally and systemically) and prolonging of developmental time (locally and systemically). 3 Previous rust infection enhanced systemically the willow's susceptibility towards subsequent fungal infection. Previous herbivore feeding on the willow had no effects on the herbivore's developmental time and mortality. However, feeding upon previously feeding‐damaged willow leaves significantly reduced larval weight.     

Leaf phenolics of three willow clones differing in resistance to Melampsora rust infection

Leaf phenolic composition in three Salix myrsinifolia Salisb. clones (V8, V45, and V43), inoculated with Melampsora rust, was analyzed to detect local rust-induced alterations during different stages of infection (2, 7, and 21 days after inoculation [DAI]). Phenolic levels and percentage of uredial area varied significantly between clones. In the most resistant clone,V8, the levels of some phenolic compounds were lower in rust-infected plants than in control plants at the initial stages of rust infection, suggesting a rapid response of phenolic metabolism to rust attack. Moreover, the clone V8 contained the highest constitutive (+)-catechin level. In clone V45, rust infection caused the most pronounced increase in the levels of individual phenolics at 7 DAI. This increase may have been effective in retarding the subsequent spread and development of rust. In the most susceptible clone V43, rust-induced phenolic responses were less pronounced and delayed. The results suggest that in specific willow-rust interactions, constitutive levels of phenolics, as well as induced phenolic responses, may contribute to the expression of rust resistance. In general, rust-induced alterations in willow phenolic levels are highly specific to genotype and compound and vary depending on the stage of rust development.     

Growth responses of selected clones of birch (Betula pendula roth.,B. pubescens Ehrh.) and willow (Salix caprea L.,S. cinerea L.) to nitrogen in solution culture

Summary Growth of selected clones of birch and willow obtained from nitrogen deficient soils was compared with that of unselected controls in pot experiments using three levels of nitrogen. Unselected controls of both genera continued shoot growth, albeit very slowly, with a very low level of nitrogen (5 ppm), while selected clones of birch grew significantly more than the controls. Selected clones of willow, on the other hand, ceased shoot growth after 10 weeks with this low nitrogen treatment. Nevertheless, they remained healthy, their leaves containing similar concentrations of nitrogen to those of the plants which continued stem growth throughout the experiment. Furthermore, they had very high root: shoot ratios compared with those of control willows and both selected and unselected birch. The two genera may have developed different mechanisms for tolerating low nitrogen, birch producing a small, relatively efficient root system; willow a larger but less efficient one. Both appear equally effective in ensuring survival on low-nitrogen sites in the field since all the selected clones were obtained from such sites and have survived well in field trials on similar sites. Both birch and willow responded toincreased nitrogen availability with increasing shoot growth and a relative decline in root growth. However, whereas in willow the unselected plants responded significantly more than selected clones, a similar but less markeddifference was found in birch. It appears that in both genera, as in herbaceous plants originating from nitrogen deficient sites, selected clones are less able to respond to increasing nitrogen supply than control plants from more fertile habitats. Attempts to correlate the response of the selected clones to nitrogen in this experiment with that to added nitrogen fertilizer in field trials has been unsuccessful. Further work is required to determine the importance of the many interacting factors which influence the response of young trees to nitrogen under the unusual field conditions associated with restored mineral workings.     

The effects of a rust infection on fitness components in a natural population of Tolumnia variegata (Orchidaceae)

The effects of a rust infection (Sphenosphora saphena, Basidiomycetes) on several fitness components of the orchid Tolumnia (Oncidium) variegata were quantified in a subtropical moist forest of Puerto Rico. Infected and uninfected plants of two size categories were observed and manipulated by increasing natural levels of fruit production to determine the effects of infection on short and long-term sexual reproduction, subsequent vegetative and reproductive growth, and mortality. Under artificially high levels of fruit production, infection had no effect on short or long-term reproduction through male or female function except for a modest decline in seed viability in small plants. Under natural levels of fruit production, infection was only related to a reduction in the number of leaves per shoot. At artificially high levels of fruit production, infection reduced leaf length, leaf width, and the number of live shoots. Survival was not associated with rust occurrence. The rust appears to have minor ecological impact on this orchid population.     

Leaf rust induced volatile organic compounds signalling in willow during the infection

Plants are known to emit volatile organic compounds (VOC) in response to various biotic or abiotic stresses. Although the VOC emission in the case of insect attacks is well described, there is only little known about the impact of pathogens on plant emission. In the present study, we used a willow-leaf rust system to describe the effects of a biotrophic fungal infection on the VOC emission pattern of willow leaves. We detected that isoprene emissions from rust-infected leaves decreased threefold compared to control. The total monoterpene emissions did not change although a stress-signalling compound (Z)-β-ocimene showed an increase in infected plants on several days. The infection also increased the emission of sesquiterpenes and lipoxygenase products (LOX) by factors of 175-fold and 10-fold, respectively. The volatile emission signals showed two clear peaks during the experiment. At 6, 7 and 12 days post-infection (dpi), the relative volatile emission signal increased to about sixfold compared to uninfected plants. These time points are directly connected to rust infection since at 6 dpi the first rust pustules appeared on the leaves and at 12 dpi necrosis had developed around several pustules. We present correlations between LOX and sesquiterpene emission signals, which suggest at least two different steps in eliciting the volatile emission.     

Increased CO2 and nutrient status changes affect phytomass and the production of plant defensive secondary chemicals in Salix myrsinifolia (Salisb.)

The effect of CO₂ enrichment (700 and 1050 ppm) on phytomass, soluble sugars, leaf nitrogen and secondary chemicals of three Salix myrsinifolia clones was studied in plants cultivated at very poor (sand seedlings) and moderate (peat seedlings) nutrient availability and under low illumination. The total shoot phytomass production of sand scedlings was less than 10% of that of the peat seedlings. Carbon dioxide increased the total shoot phytomass of peat seedlings. When the ambient carbon supply was doubled (to 700 ppm) the growth of sand seedlings was slightly enhanced but 1050 ppm CO₂ gave growth figures similar to those at the control CO₂ level. Leaf nitrogen content and total soluble sugar contents were significantly higher in peat seedlings than in sand seedlings. Leaf nitrogen showed a decreasing trend in relation to CO₂ increase. On the other hand, CO₂ did not have any clear-cut effect on total sugars. At the control CO₂ level the content of salicortin, which is a dynamic phenolic, was higher in the peat seedlings than in the sand seedlings, but salicin showed the opposite trend. CO₂ enrichment considerably decreased these phenolics in the peat seedlings. At the control CO₂ level, the content of more static phenolics, such as proanthocyanidins, was higher in sand seedlings. An increased carbon supply considerably increased static phenolics in the peat seedlings. Willow defence against generalist herbivores is moderately decreased by enhancement of atmospheric carbon dioxide.     

Effects of light and nutrient availability on the growth,allocation, carbon/nitrogen balance,phenolic chemistry,and resistance to herbivory of two freshwater macrophytes

Phenotypic responses of Potamogeton amplifolius and Nuphar advena to different light (7% and 35% of surface irradiance) and nutrient environments were assessed with field manipulation experiments. Higher light and nutrient availability enhanced the growth of P. amplifolius by 154% and 255%, respectively. Additionally, biomass was allocated differently depending on the resource: high light availability resulted in a higher root/shoot ratio, whereas high nutrient availability resulted in a lower root/shoot ratio. Low light availability and high nutrient availability increased the nitrogen content of leaf tissue by 53% and 40% respectively, resulting in a 37% and 31% decrease in the C/N ratio. Root nitrogen content was also increased by low light and high nutrient availability, by 50% (P=0.0807) and 77% respectively, resulting in a 20% and 40% decrease in root C/N ratio. Leaf phenolics were significantly increased 72% by high light and 31% by high nutrient availability, but root phenolic concentrations were not altered significantly. None of these changes in tissue constituents resulted in altered palatability to crayfish. N. advena was killed by the same high nutrient treatment that stimulated growth in P. amplifolius, preventing assessment of phenotypic responses to nutrient availability. However, high light availability increased overall growth by 24%, but this was mainly due to increased growth of the rhizome (increased 100%), resulting in a higher root/shoot ratio. High light tended to increase the production of floating leaves (P=0.09) and significantly decreased the production of submersed leaves. High light availability decreased the nitrogen content by 15% and 25% and increased the phenolic concentration by 88% and 255% in floating and submersed leaves, respectively. These differences in leaf traits did not result in detectable differences in damage by herbivores.     

Beetle grazing reduces natural infection of Rumex obtusifolius by fungal pathogens

In previously reported laboratory experiments, infection of Rumex obtusifolius by the rust fungus Uromyces rumicis was decreased on leaves which had prior herbivory by the beetle Gastrophysa viridula . In this paper we investigate whether this interaction is robust for natural infection by a variety of fungi in field experiments carried out in spring and autumn with plants given different levels of nitrogen fertilization. Grazing by G. viridula led to a decrease in lesion density of Ramularia rubella and Venturia rumicis in the spring and V. rumicis and U. rumicis in the autumn experiment. For V. rumicis and U. rumicis significant reductions in lesion density occurred on the undamaged leaves of damaged plants, compared with similar leaves on undamaged plants, suggesting systemic induced resistance. This induced resistance was usually independent of the amount of nitrogen fertilization, although the inhibitory effect of grazing on R. rubella in the spring and V. rumicis in the autumn experiment was enhanced by increasing nitrogen fertilization and was inhibited by increasing nitrogen fertilization for V. rumicis in the spring. In both experiments, the lesion density of V. rumicis was greater on leaves on which R. rubella was also present, and the presence of U. rumicis in the autumn experiment was linked to a similar but greater effect on V. rumicis lesion density. We found no evidence of induced resistance by fungi against fungi in these experiments. We highlight the complex interactions between inhibitory and facilitatory processes acting on leaf fungal infection. These results are compared with the proposed molecular mechanisms of induced resistance(s) and we consider the benefits of closer integration between molecular and ecological investigations of induced resistances that occur in the field.     

Rapid accumulation of trihydroxy oxylipins and resistance to the bean rust pathogen Uromyces fabae following wounding in Vicia faba

BACKGROUND AND AIMS: Insect damage to plants leads to wound-activated responses directed to healing of damaged tissues, as well as activation of defences to prevent further insect damage. Negative cross-talk exists between the jasmonic acid-based signalling system that is activated upon insect attack and the salicylic acid-based system frequently activated following pathogen infection. Thus, insect attack may compromise the ability of the plant to defend itself against pathogens and vice versa. However, insect herbivory and mechanical wounding have been shown to reduce fungal infections on some plants, although the underlying mechanisms remain to be defined. This work examines the effects of mechanical wounding on rust infection both locally and systemically in the broad bean, Vicia faba and follows changes in oxylipins in wounded leaves and unwounded leaves on wounded plants. METHODS: The lamina of first leaves was wounded by crushing with forceps, and first and second leaves were then inoculated, separately, with the rust Uromyces fabae at various times over a 24 h period. Wounded first leaves and unwounded second leaves were harvested at intervals over a 24 h period and used for analysis of oxylipin profiles. KEY RESULTS Mechanical wounding of first leaves of broad bean led to significantly reduced rust infection in the wounded first leaf as well as the unwounded second leaf. Increased resistance to infection was induced in plants inoculated with rust just 1 h after wounding and was accompanied by rapid and significant accumulation of jasmonic acid and two trihydroxy oxylipins in both wounded first leaves and unwounded second leaves. The two trihydroxy oxylipins were found to possess antifungal properties, reducing germination of rust spores. CONCLUSIONS: These results demonstrate the rapidity with which resistance to pathogen infection can be induced following wounding and provides a possible mechanism by which pathogen infection might be halted.     

Approaches on vegetative propagation of difficult-to-root <Emphasis Type="Italic">Salix caprea</Emphasis>

In the framework of a willow rust research project, it was necessary to include vegetatively propagated plant material of selected sallow trees (Salix caprea L.) into biotests for identification of pathotypes. Since it was not possible to root sufficient clonal plants by conventional cutting propagation, the applicability of tissue culture methods was tested. From 10 selected donor trees of Salix caprea newly sprouted shoots were harvested and transferred to nutrient media after surface disinfection. The cultures were grown at 20--22 °C, illuminated with warm-white fluorescent tubes. The majority of shoot tips and nodal segments died during the first month, but only with nursery-grown plants this was caused by bacteria contamination. Two clones could be established easily on hormone-free medium. Five clones could be initiated only after repeated subcultures on various media variants. Three clones failed completely. Different basic media compositions were tested and Woody Plant Medium, supplemented with 0.1% activated charcoal, proved to be best for most of the sallow clones. Well developed rooted plantlets were used in vitro for microcutting propagation. The resulting plants were transferred to soil and could be included in the rust screening program after acclimatising. The applicability of micropropagation for selected Salix caprea donor trees was strongly depending on the genotype. But the comparison of results from microcuttings with conventional cutting propagation showed that these methods were successful for different clones each.     

Maximal biomass production can occur in corn (Zea mays) in the absence of NO3 accumulation in either leaves or roots

In order to investigate effects of limited NO₃ availability in corn ( Zea mays L. cv. Brulouis) 17-day-old plants were grown for a further 25 days on sand in a growth chamber. The plants received frequent irrigation with a complete nutrient solution containing 0.2, 0.6, 1.5 or 3.0 mM NO₃. With 0.2 mM NO; nitrate levels in both roots and leaves diminished rapidly and were almost zero after 10 days treatment. Concurrently, as signs of nitrogen deficiency appeared, shoot growth was restricted, whereas root growth was enhanced. In addition, the concentration of reduced nitrogen and malate in the leaves declined, and in vitro nitrate reductase activity (NRA. EC 1.6.6.1), soluble protein and chlorophyll levels of leaf tissue were depressed and starch concentration was enhanced. With 0.6 mM NO₃ in the nutrient solution, the decrease in NO₃ levels in the tissues and the increase in root development were similar to those observed with 0.2 mM NO₃. However, shoot growth, reduced nitrogen concentration in leaves, and the above-mentioned biochemical characteristics were almost identical to those obtained at 1.5 and 3.0 mM NO₃. This indicates that when supplied with 0.6 mM NO₃, corn plants were able to absorb sufficient NO3 to support maximal biomass production without appreciable NO₃ accumulation in roots or shoot. It is, thus, suggested that the plants responded to low NO₃, availability in medium by enhancing root growth and by maximizing NO₃ reduction relative to NO₃ accumulation.     

The effect of nitrogen fertilization and rust fungus infection, singly and combined, on the leaf chemical composition of Rumex obtusifolius

1. The chrysomelid beetle Gastrophysa viridula occurs on Rumex obtusifolius growing in a range of nutrient conditions and also on plants infected with the foliar fungus Uromyces rumicis . In a controlled environment, we investigated the effect of fertilizing plants with eight nitrate and four ammonium concentrations, with or without infection, on leaf nutritional quality.
2. Increasing nitrate fertilization increased leaf oxalate, total nitrogen and nitrate concentrations and water content, and decreased total non-structural carbohydrate (NSC) concentrations. Increasing ammonium fertilization increased leaf nitrogen concentration and water content, decreased nitrate and NSC concentrations, and had no effect on oxalate concentrations.
3. Infection produced a mainly additive effect to fertilization, increasing NSC and oxalate, and decreasing nitrate and nitrogen concentration in whole plants fed nitrate, and increasing nitrate and NSC in whole plants fed ammonium.
4. Young leaves on infected plants remained uninfected and had greater nitrogen and NSC concentrations, and lower oxalate and nitrate concentrations, than infected leaves on the same plant.
5. These results are discussed in relation to changes in C:N and NSC:organic nitrogen ratios, the effect of nitrate and oxalate, and the known feeding and oviposition preferences of the beetle. The results suggest that there is an optimum nitrogen fertilization level for G. viridula development.     

Shoot growth dynamics and photosynthetic response to increased nitrogen availability in the alpine willow Salix glauca

Plants subjected to increases in the supply of resource(s) limiting growth may allocate more of those resources to existing leaves, increasing photosynthetic capacity, and/or to production of more leaves, increasing whole-plant photosynthesis. The responses of three populations of the alpine willow, Salix glauca, growing along an alpine topographic sequence representing a gradient in soil moisture and organic matter, and thus potential N supply, to N amendments, were measured over two growing seasons, to elucidate patterns of leaf versus shoot photosynthetic responses. Leaf-(foliar N, photosynthesis rates, photosynthetic N-use efficiency) and shoot-(leaf area per shoot, number of leaves per shoot, stem weight, N resorption efficiency) level measurements were made to examine the spatial and temporal variation in these potential responses to increased N availability. The predominant response of the willows to N fertilization was at the shoot-level, by production of greater leaf area per shoot. Greater leaf area occurred due to production of larger leaves in both years of the experiment and to production of more leaves during the second year of fertilization treatment. Significant leaflevel photosynthetic response occurred only during the first year of treatment, and only in the dry meadow population. Variation in photosynthesis rates was related more to variation in stomatal conductance than to foliar N concentration. Stomatal conductance in turn was significantly related to N fertilization. Differences among the populations in photosynthesis, foliar N, leaf production, and responses to N fertilization indicate N availability may be lowest in the dry meadow population, and highest in the ridge population. This result is contrary to the hypothesis that a gradient of plant available N corresponds with a snowpack/topographic gradient.     

The influence of nitrogen availability on carbon and nitrogen storage in the biennial Cirsium vulgare (Savi) Ten. I. Storage capacity in relation to resource acquisition, allocation and recycling

Plants of Cirsium vulgare (Savi) Ten. were cultivated under five different nitrogen regimes in order to investigate the effects of nitrogen supply on the storage processes in a biennial species during its first year of growth. External N supply increased total biomass production without changing the relationship between ‘productive plant compartments’ (i.e. shoot plus fine roots) and ‘storage plant compartments’ (i.e. structural root dry weight, which is defined as the difference between tap root biomass and the amount of stored carbohydrates and N compounds). The amount of carbohydrates and N compounds stored per unit of structural tap root dry weight was not affected by external N availability during the season, because high rates of N supply increased the concentration of N compounds whilst decreasing the carbohydrate concentration, and low rates of N supply had the opposite effect. Mobilization of N from senescing leaves was not related to the N status of the plants. The relationship between nitrogen compounds stored in the tap root and the maximum amount of nitrogen in leaves was an increasing function with increasing nitrogen supply. We conclude that the allocation between vegetative plant growth and the growth of storage structures over a wide range of N availability seems to follow predictions from optimum allocation theory, whereas N storage responds in a rather plastic way to N availability.     

Genotypic Tannin Levels in Populus tremula Impact the Way Nitrogen Enrichment Affects Growth and Allocation Responses for Some Traits and Not for Others

Plant intraspecific variability has been proposed as a key mechanism by which plants adapt to environmental change. In boreal forests where nitrogen availability is strongly limited, nitrogen addition happens indirectly through atmospheric N deposition and directly through industrial forest fertilization. These anthropogenic inputs of N have numerous environmental consequences, including shifts in plant species composition and reductions in plant species diversity. However, we know less about how genetic differences within plant populations determine how species respond to eutrophication in boreal forests. According to plant defense theories, nitrogen addition will cause plants to shift carbon allocation more towards growth and less to chemical defense, potentially enhancing vulnerability to antagonists. Aspens are keystone species in boreal forests that produce condensed tannins to serve as chemical defense. We conducted an experiment using ten Populus tremula genotypes from the Swedish Aspen Collection that express extreme levels of baseline investment into foliar condensed tannins. We investigated whether investment into growth and phenolic defense compounds in young plants varied in response to two nitrogen addition levels, corresponding to atmospheric N deposition and industrial forest fertilization. Nitrogen addition generally caused growth to increase, and tannin levels to decrease; however, individualistic responses among genotypes were found for height growth, biomass of specific tissues, root:shoot ratios, and tissue lignin and N concentrations. A genotype’s baseline ability to produce and store condensed tannins also influenced plant responses to N, although this effect was relatively minor. High-tannin genotypes tended to grow less biomass under low nitrogen levels and more at the highest fertilization level. Thus, the ability in aspen to produce foliar tannins is likely associated with a steeper reaction norm of growth responses, which suggests a higher plasticity to nitrogen addition, and potentially an advantage when adapting to higher concentrations of soil nitrogen.     

The effect and transmission of one isolate of the rust Puccinia minussensis on five clones of Lactuca sibirica

In a greenhouse experiment, one isolate of the systemic rust fungus Puccinia minussensis was applied to the host clone from which it was collected and to four other clones of the host Lactuca sibirica. The plants were grown in fertilized potting compost (N+) to promote growth and in peat (N-) to hamper growth, for three growing periods during one year. The results show that the expression of host plant resistance could not be determined visually, but there were differences in effects on the clones. The rust isolate was found to produce a significantly higher percentage of diseased shoots on clone A (the clone it was taken from). Furthermore, the rust also had the strongest effect on both biomass and shoot production on clone A compared to the other four clones. The data suggest that the rust isolate is highly adapted to the clone from which it originated. We suggest that selection in this system has not favoured a benign pathogen and that similar patterns are likely to occur for plants that (i) rarely establish by seeds; (ii) have strong lateral growth; and (iii) may persist for long periods once established.     

Methyl jasmonate stimulates polyamines biosynthesisand resistance against leaf rust in wheat plants

Abstract

Leaf rust of wheat (Triticum aestivum L.), incited by Puccinia recondita ex Desm. f. sp. tritici Eriks, is one of the most important wheat diseases in Egypt. Methyl jasmonate (MJ) is a potential plant elicitor which induces a wide range of chemical and anatomical defense reactions in conifers and might be used to increase systemic resistance against biotic damage. In the greenhouse, different concentrations of MJ (10, 20 and 30 mM) were applied as seed soaking plus foliar spray or only as foliar spray to control leaf rust and induction of secondary compound production in leaves of wheat plants. Foliar spray was applied after 30 and 50 days of sowing. Results indicated that all concentrations and treatments reduced the severity of rust disease caused by P. recondita f. sp. tritici in wheat leaves during 45 days of inoculations. Disease incidence was decreased significantly in MJ-treated plants as seed soaking plus foliar spray with 20 and 30 mM when compared to 10 mM MJ or control plants. The study revealed that, with increasing concentrations of MJ, the secondary metabolites were greatly increased. Endogenous levels of both free and conjugated putrescine, spermidine and spermine increased in response to the elicitor. Activities of polyamine biosynthetic enzymes of ornithine decarboxylase (ODC) and polyamine oxidase (PAO) displayed up to threefold increases relative to untreated control. Moreover, significant increases in activities of plant defense-related protein, enzymes as peroxidase and chitinase as well as free and conjugated phenols contents were recorded in treated plants compared with untreated and infected plants. Furthermore, MJ treatment increased the chlorophyll-a, chlorophyll-b and carotenoids pigments contents, the higher increase was obtained with combined treatment between seeds soaking plus foliar spray at 20 and 30 mM of MJ. Under field conditions, three concentrations of MJ, i.e. 10, 20 and 30 mM as combined treatment between seeds soaking plus foliar spray or only as foliar spray were applied to study their effect against rust disease. Foliar spray was applied after 30 and 80 days of sowing. Results showed that the high reduction in disease severity was obtained with combined treatments between seeds soaking plus foliar spray with MJ at 20 and 30 mM compared with other treatments and control. At the same time, all treatments increased the growth and grain yield of wheat plants. It could be suggested that combination treatment between seeds soaking plus foliar spray with methyl jasmonate might be used commercially for controlling rust disease of wheat plants under field conditions.     

Effects of Resource Availability on Carbon Allocation and Developmental Instability in Cloned Birch Seedlings

Abundant nitrogen improves seedling growth and establishment. Vigorous growth brings about changes in rates and patterns of plant development and changes in the relationship between primary and secondary metabolism, which may make seedlings more susceptible to herbivores and pathogens than are slow-growing seedlings. We studied how nitrogen fertilization and manual defoliation of source leaves affect growth, carbon allocation, and developmental instability in cloned seedlings of white birch (Betula pubescens Ehrh.). Biomass was higher, whereas concentrations of most classes of phenolic compounds were lower in the nitrogen-rich environment. Interestingly, fertilization did not change the concentrations of cell wall-bound proanthocyanidins, which represent an important fraction of the group of phenolic compounds. Nitrogen enrichment increased levels of fluctuating asymmetry, an index of developmental instability. This result confirms that not only stress but also any deviation from normal resource availability may increase leaf developmental instability in birches. In contrast to fertilization, a one-time defoliation of source leaves did not shape seedling growth, development, or carbon allocation. This could be the result of compensatory growth or of the fact that the defoliation treatment was not strong enough to induce detectable effects until the end of the growing season.     

Role of an endogenous nitric oxide burst in the resistance of wheat to stripe rust

The stripe rust (or yellow rust) disease caused by Puccinia striiformis Westend is a serious disease of wheat in many areas of the world. The role of NO, which is an important redox‐active signalling molecule in plants, was investigated in the wheat‐stripe rust system. The phenotypes from interactions of the same wheat variety, Lovrin10, with two different clones of stripe rust strains (P. striiformis Westend), namely China yellow rust (CY)22‐2 and CY29‐1, which are immune and susceptible reaction types, respectively. The time course of host endogenous NO detected by electron spin resonance indicated that recognition of an avirulent strain was associated with two peaks of NO production. The first peak of NO accumulated in the early infection stage whereas the second peak accumulated in the latent period; however, only a single peak of NO was observed in the latent period for the virulent strain. Furthermore, the activity of pathogen‐related protein‐phenylalanine ammonia‐lyase was higher in the resistant system than in the susceptible system, which suggested that the first NO production was associated with resistance. Exogenous NO improved the activity of phenylalanine ammonia‐lyase and induced a resistant response of Lovrin10 to the virulent strain CY29‐1, thereby providing further evidence that the first peak of NO production was associated with resistance. These results indicate that the first NO burst in the immune system plays an important role in the resistant reaction of wheat to strip rust.