Quantitative patterns between plant volatile emissions induced by biotic stresses and the degree of damage

Plants have to cope with a plethora of biotic stresses such as herbivory and pathogen attacks throughout their life cycle. The biotic stresses typically trigger rapid emissions of volatile products of lipoxygenase (LOX) pathway (LOX products: various C(6) aldehydes, alcohols, and derivatives, also called green leaf volatiles) associated with oxidative burst. Further a variety of defense pathways is activated, leading to induction of synthesis and emission of a complex blend of volatiles, often including methyl salicylate, indole, mono-, homo-, and sesquiterpenes. The airborne volatiles are involved in systemic responses leading to elicitation of emissions from non-damaged plant parts. For several abiotic stresses, it has been demonstrated that volatile emissions are quantitatively related to the stress dose. The biotic impacts under natural conditions vary in severity from mild to severe, but it is unclear whether volatile emissions also scale with the severity of biotic stresses in a dose-dependent manner. Furthermore, biotic impacts are typically recurrent, but it is poorly understood how direct stress-triggered and systemic emission responses are silenced during periods intervening sequential stress events. Here we review the information on induced emissions elicited in response to biotic attacks, and argue that biotic stress severity vs. emission rate relationships should follow principally the same dose–response relationships as previously demonstrated for different abiotic stresses. Analysis of several case studies investigating the elicitation of emissions in response to chewing herbivores, aphids, rust fungi, powdery mildew, and Botrytis, suggests that induced emissions do respond to stress severity in dose-dependent manner. Bi-phasic emission kinetics of several induced volatiles have been demonstrated in these experiments, suggesting that next to immediate stress-triggered emissions, biotic stress elicited emissions typically have a secondary induction response, possibly reflecting a systemic response. The dose–response relationships can also vary in dependence on plant genotype, herbivore feeding behavior, and plant pre-stress physiological status. Overall, the evidence suggests that there are quantitative relationships between the biotic stress severity and induced volatile emissions. These relationships constitute an encouraging platform to develop quantitative plant stress response models

Volatiles of Conifer Seedlings : Compositions and Resistance Markers

Pine weevils cause major damage to newly planted conifer seedlings in reforestation areas. However, recent findings indicate that small (“mini”) seedlings, planted at the age of 7-10 weeks, are gnawed less by pine weevils than the larger, conventionally planted seedlings. Thus, it has been proposed that planting young conifer seedlings in clear-cut areas may reduce the damage caused by pine weevils. In attempts to determine why mini seedlings appear to be less damaged by pine weevils than “conventional” seedlings, the volatiles released by Norway spruce and Scots pine mini seedlings were investigated, since such chemicals are of great importance in herbivore-plant communication, inter alia acting as repellents, attractants or antifeedants. Volatiles from the seedlings were collected, separated and identified by solid phase microextraction (SPME) followed by gas chromatography-mass spectrometry. The results show that there are high levels of chemodiversity among both spruce and pine seedlings. Between-tissue and age-related variations in their emissions were also found. Norway spruce clones infested by mites were also examined to assess genotype- and pest-specific stress reactions of Norway spruce. Finally, the effects of certain spruce defense compounds on the behavior of the large pine weevil Hylobius abietis were examined.QC 2010081

Combined Acute Ozone and Water Stress Alters the Quantitative Relationships between O3 Uptake, Photosynthetic Characteristics and Volatile Emissions in Brassica nigra

Ozone (O3) entry into plant leaves depends on atmospheric O3 concentration, exposure time and openness of stomata. O3 negatively impacts photosynthesis rate (A) and might induce the release of reactive volatile organic compounds (VOCs) that can quench O3, and thereby partly ameliorate O3 stress. Water stress reduces stomatal conductance (gs) and O3 uptake and can affect VOC release and O3 quenching by VOC, but the interactive effects of O3 exposure and water stress, as possibly mediated by VOC, are poorly understood. Well-watered (WW) and water-stressed (WS) Brassica nigra plants were exposed to 250 and 550 ppb O3 for 1 h, and O3 uptake rates, photosynthetic characteristics and VOC emissions were measured through 22 h recovery. The highest O3 uptake was observed in WW plants exposed to 550 ppb O3 with the greatest reduction and poorest recovery of gs and A, and elicitation of lipoxygenase (LOX) pathway volatiles 10 min–1.5 h after exposure indicating cellular damage. Ozone uptake was similar in 250 ppb WW and 550 ppb WS plants and, in both treatments, O3-dependent reduction in photosynthetic characteristics was moderate and fully reversible, and VOC emissions were little affected. Water stress alone did not affect the total amount and composition of VOC emissions. The results indicate that drought ameliorated O3 stress by reducing O3 uptake through stomatal closure and the two stresses operated in an antagonistic manner in B. nigra

Combined acute ozone and water stress alters the quantitative relationships between O₃ uptake, photosynthetic characteristics and volatile emissions in Brassica nigra

Ozone and water stress effects on Brassica nigra volatile organic compounds emission (VOC) and photosynthetic characteristics. VOCs were collected on adsorbent cartridges and analyzed with GC-MS. Ozone exposures were 250 ppb O₃ for well-watered and 550 ppb O₃ for well-watered and water-stressed B. nigra plants.European Commission through European Research Council (advanced grant 322603, SIP-VOL+) and the European Regional Development Fund (Centre of Excellence EcolChange), and from the Estonian Research Council (team grant PRG537) and the Estonian University of Life Sciences (grant P180273PKTT)

Powdery mildew (Erysiphe cruciferarum) evaluation on oilseed rape and alternative cruciferous oilseed crops in the northern Baltic region in unusually warm growing seasons

The pathogen Erysiphe cruciferarum is an increasingly serious threat to cruciferous oilseed crops worldwide. In the present study, the severity of powdery mildew was evaluated on spring oilseed rape (Brassica napus) and five alternative oilseed crop species (B. juncea, B. nigra, Sinapis alba, Raphanus sativus, Eruca sativa). The main aim of the study was to identify plant species that are less susceptible to powdery mildew for possible application as cover crop, in trap cropping or seed production. Powdery mildew assessments were conducted in two growing seasons that were characterised by unusually warm and dry conditions for northern temperate climatic conditions. In both growing seasons, a heavy powdery mildew infection (over 80%) was recorded on B. napus and B. nigra plants, indicating that E. cruciferarum is an important pathogen for oilseed crops in northern Baltics. However, three other cruciferous species S. alba, E. sativa and R. sativus showed full resistance to powdery mildew, and thus, even under strong powdery mildew pressure, they can be cultivated without pesticide application in northern Baltic conditions. We suggest that in changing climatic conditions powdery mildew is expected to become a more serious problem in cruciferous oilseed crops in northern Europe, especially under intensive short-rotation farming practices

Drought-tolerance of wheat improved by rhizosphere bacteria from harsh environments

Water is the key resource limiting world agricultural production. Although an impressive number of research reports have been published on plant drought tolerance enhancement via genetic modifications during the last few years, progress has been slower than expected. We suggest a feasible alternative strategy by application of rhizospheric bacteria coevolved with plant roots in harsh environments over millions of years, and harboring adaptive traits improving plant fitness under biotic and abiotic stresses. We show the effect of bacterial priming on wheat drought stress tolerance enhancement, resulting in up to 78% greater plant biomass and five-fold higher survivorship under severe drought. We monitored emissions of seven stress-related volatiles from bacterially-primed drought-stressed wheat seedlings, and demonstrated that three of these volatiles are likely promising candidates for a rapid non-invasive technique to assess crop drought stress and its mitigation in early phases of stress development. We conclude that gauging stress by elicited volatiles provides an effectual platform for rapid screening of potent bacterial strains and that priming with isolates of rhizospheric bacteria from harsh environments is a promising, novel way to improve plant water use efficiency. These new advancements importantly contribute towards solving food security issues in changing climates

Alternaria Black Spot (Alternaria brassicae) Infection Severity on Cruciferous Oilseed Crops

The increase in the cultivation area of cruciferous oilseed crops and the use of short crop rotation has resulted in the enhanced spread of several major pests in Northern latitudes. There is currently limited information about incidence and severity of Alternaria black spot disease (Alternaria brassicae) on the main oilseed crop, spring oilseed rape (Brassica napus), in the Northern Baltics. Thus, spring oilseed rape and five alternative cruciferous oilseed crops were selected and their resistance to black spot disease was evaluated in field conditions during two growing seasons. We hypothesized that spring oilseed rape is more susceptible to Alternaria black spot disease than other alternative cruciferous oilseed crops. Both growing seasons were warmer and drier compared to the long-term average, and were thus suitable for A. brassicae development and assessments. In both years, incidence of Alternaria black spot infection was recorded on all cruciferous species, yet the disease development differed considerably among the crops. During both growing seasons, black mustard (B. nigra) plants were the most infected. Based on our observations during warm growing seasons we conclude that alternative oilseed crops such as Sinapis alba, Eruca sativa and Raphanus sativus are more resistant to the Alternaria black spot infection than the traditional oilseed crops and thus, possess a great potential to grow with limited chemical disease control in Northern Baltic conditions

Enhancement of wheat (<i>Triticum aestivum</i>) drought tolerance by <i>Bacillus thuringiensis</i> AZP2 and <i>Paenibacillus polymyxa</i> B in sand soil.

<p>Panel A demonstrates the effect of AZP2 and B priming on seedlings survival after a severe 10-day drought stress episode. Panel B shows the effect of AZP2 priming on whole plant dry mass after 8 days growth without watering. The statistical analysis in (A) is based on a three-way ANOVA (stress, strains (i.e. AZP2 and B) and stress exposure time). ANOVA was conducted on two plant groups with 16 replicates in each group. *** indicate highly significant effects for the tested factor at <i>P≤</i>0.01. In B, eight independent experiments were performed, and treatments labelled with the same letter are not significantly different at <i>P≤</i>0.01.</p

Temporal variations in the emission rates of some benzenoids and terpenoids emitted by wheat plants.

<p>Benzaldehyde (A), β-pinene (B) and geranyl acetone (C) emission rates from leaves of drought-stressed (0, 2, 5, 8 and 10 days without water) wheat plants after priming with <i>Bacillus thuringiensis</i> AZP2 are demonstrated. The error bars indicate +SE for three biological replicates. Statistical analysis and levels of significance as in Fig. 4.</p

Effect of priming by <i>Bacillus thuringiensis</i> AZP2 on wheat <i>(Triticum aestivum L. cv. Stava)</i> on average (±SD) growth characteristics, water use efficiency and antioxidant enzyme activities.

1<p>Analysis of plant root was conducted by Root Reader3D Imaging and Analysis System and manually <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0096086#pone.0096086-Niinemets1" target="_blank">[7]</a>.</p>2<p>Twelve plants per treatment were sampled. Roots with adhering soil (RAS) were carefully separated from bulk soil by shaking. Soil and root dry mass (RT) was recorded after drying the samples at 105°C, and RAS/RT ratio was calculated.</p>3<p>Twelve plants were carefully separated from soil by shaking followed by washing the roots in distilled water and left to drain in Petri dishes with water to maintain humidity. Root system characteristics were evaluated by Zeiss LSM 710 microscope.</p>4<p>Water use efficiency is defined as the ratio of total plant dry mass per total water used.</p>5<p>MDHAR - Monodehydroascorbate reductase, GR- Glutathione reductase, SOD- Superoxide dismutase, CAT-Catalase.</p><p>See Materials and Methods for enzyme extraction and activity measurements.</p><p>*Means followed by the same letter are not significantly different at p≤0.01. See Experimental procedures.</p