Plant Defence Research Papers - Academia.edu (original) (raw)

Plant disease control is mainly based on the use of fungicides, bactericides, and insecticides-chemical compounds toxic to plant invaders, causative agents, or vectors of plant diseases. However, the detrimental effect of these chemicals... more

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

SUMMARY Control of grapevine virus and phytoplasma diseases is currently based on prophylactic measures and cultur- al practices. Certification programs aim to avoid the in- troduction of diseased grapevines into healthy vine- yards, and... more

SUMMARY Control of grapevine virus and phytoplasma diseases is currently based on prophylactic measures and cultur- al practices. Certification programs aim to avoid the in- troduction of diseased grapevines into healthy vine- yards, and cultural practices aim to reduce the popula- tions of virus vectors to limit virus spread. These ap- proaches however are of limited effectiveness. Addition- ally, there

Cassava is an important dietary component for over 1 billion people, and its ability to yield under drought has led to it being promoted as an important crop for food security under climate change. Despite its known photosynthetic... more

Cassava is an important dietary component for over 1 billion people, and its ability to yield under drought has led to it being promoted as an important crop for food security under climate change. Despite its known photosynthetic plasticity in response to temperature, little is known about how temperature affects plant toxicity or about interactions between temperature and drought, which is important because cassava tissues contain high levels of toxic cya-nogenic glucosides, a major health and food safety concern. In a controlled glasshouse experiment, plants were grown at 2 daytime temperatures (23 °C and 34 °C), and either well-watered or subject to a 1 month drought prior to harvest at 6 months. The objective was to determine the separate and interactive effects of temperature and drought on growth and toxicity. Both temperature and drought affected cassava physiology and chemistry. While temperature alone drove differences in plant height and above-ground biomass, drought and temperature 9 drought interactions most affected tuber yield, as well as foliar and tuber chemistry, including C : N, nitrogen and cyanide potential (CNp; total cyanide released from cyanogenic glucosides). Conditions that most stimulated growth and yield (well-watered 9 high temperature) effected a reduction in tuber toxicity, whereas drought inhibited growth and yield, and was associated with increased foliar and tuber toxicity. The magnitude of drought effects on tuber yield and toxicity were greater at high temperature; thus, increases in tuber CNp were not merely a consequence of reduced tuber bio-mass. Findings confirm that cassava is adaptable to forecast temperature increases, particularly in areas of adequate or increasing rainfall; however, in regions forecast for increased incidence of drought, the effects of drought on both food quality (tuber toxicity) and yield are a greater threat to future food security and indicate an increasing necessity for processing of cassava to reduce toxicity.

Globally, cassava is the second most important root crop after potatoes and the fifth most important crop overall in terms of human caloric intake. In addition to its growing global importance for feed, fuel, and starch, cassava has long... more

Globally, cassava is the second most important root crop after potatoes and the fifth most important crop overall in terms of human caloric intake. In addition to its growing global importance for feed, fuel, and starch, cassava has long been vital to food security in Sub-Saharan Africa. Climate change is expected to have its most severe impact on crops in food insecure regions, yet little is known about how cassava productivity will respond to climate change. The most important driver of climate change is globally increasing atmospheric CO2 concentration ([CO2]). However, the potential for cassava to enhance food security in an elevated [CO2] world is uncertain as greenhouse and open top chamber (OTC) study reports are ambiguous. Studies have yielded misleading results in the past regarding the effect of elevated [CO2] on crop productivity, particularly in cases where pots restricted sink growth. To resolve these conflicting results, we compare the response of cassava to growth at ambient (ca. 385 ppm) and elevated [CO2] (585 ppm) under field conditions and fully open air [CO2] elevation. After three and half months of growth at elevated [CO2], above ground biomass was 30% greater and cassava root tuber dry mass increased over 100% (fresh weight increased 89%). High photosynthetic rates and photosynthetic stimulation by elevated [CO2], larger canopies, and a large sink capacity all contributed to cassava’s growth and yield stimulation. Cassava exhibited photosynthetic acclimation via decreased Rubisco capacity early in the season prior to root tuber initiation when sink capacity was smaller. Importantly, and in contrast to a greenhouse study, we found no evidence of increased leaf N or total cyanide concentration in elevated [CO2]. All of our results are consistent with theoretical expectations; however, the magnitude of the yield increase reported here surpasses all other C3 crops and thus exceeds expectations.

Plant-associated bacteria reside in the rhizosphere, phyllosphere, and inside tissues of healthy plants. This chapter discusses concepts and examples of how naturally occurring and introduced bacteria may contribute to management of... more

Plant-associated bacteria reside in the rhizosphere, phyllosphere, and inside tissues of healthy plants. This chapter discusses concepts and examples of how naturally occurring and introduced bacteria may contribute to management of soilborne and foliar diseases. Introduced bacteria which have demonstrated biological control activity against soil-borne pathogenic fungi and nematodes include rhizobacteria (root-colonising bacteria) and endophytic bacteria (bacteria isolated from within healthy plant tissues). Recently, some introduced rhizobacteria have been found to enhance plant defences, leading to systemic protection against foliar pathogens upon seed or root-treatments with the rhizobacteria. In these cases, introduction of the rhizobacteria results in reduced damage to multiple pathogens, including viruses, fungi and bacteria. An alternative strategy to the introduction of specific antagonists is the augmentation of existing antagonists in the root environment. This augmentation may result from the use of specific organic amendments, such as chitin, which stimulate populations of antagonists, thereby inducing suppressiveness. Inter-cropping or crop rotation with some tropical legumes, including velvetbean (Mucuna deeringiana), lead to management of phytoparasitic nematodes, partly through stimulation of antagonistic microorganisms. Some biorational nematicides, such as specific botanical aromatic compounds, also appear to induce suppressiveness through alterations in the soil microbial community.

Plant-insect interactions are not just influenced by interactions between plants and the actively feeding stages, but also by the close relationships between plants and insect eggs. Here, we review both effects of plants on insect eggs... more

Plant-insect interactions are not just influenced by interactions between plants and the actively feeding stages, but also by the close relationships between plants and insect eggs. Here, we review both effects of plants on insect eggs and, vice versa, effects of eggs on plants. We consider the influence of plants on the production of insect eggs and address the role of phytochemicals for the biosynthesis and release of insect sex pheromones, as well as for insect fecundity. Effects of plants on insect oviposition by contact and olfactory plant cues are summarised. In addition, we consider how the leaf boundary layer influences both insect egg deposition behaviour and development of the embryo inside the egg. The effects of eggs on plants involve egg-induced changes of photosynthetic activity and of the plant's secondary metabolism. Except for gall-inducing insects, egg-induced changes of phytochemistry were so far found to be detrimental to the eggs. Egg deposition can induce h...

Comparison of the diets of sympatric gorillas and chimpanzees allows an analysis of niche separation between these two closely related species. Qualitatively, their diets are similar, being dominated by an equally diverse array of fruit... more

Comparison of the diets of sympatric gorillas and chimpanzees allows an analysis of niche separation between these two closely related species. Qualitatively, their diets are similar, being dominated by an equally diverse array of fruit species complemented with vegetative plant parts, seeds and insects. Gorillas eat more vegetative plant parts than do chimpanzees, but niche separation is most obvious in

Cassava (Manihot esculenta Crantz) is the staple food source for over 850 million people worldwide. Cassava contains cyanogenic glucosides and can be toxic to humans, causing paralysing diseases such as konzo, and even death if not... more

Cassava (Manihot esculenta Crantz) is the staple food source for over 850 million people worldwide. Cassava contains cyanogenic glucosides and can be toxic to humans, causing paralysing diseases such as konzo, and even death if not properly processed. Konzo epidemics are often associated with times of drought. This may be due to a greater reliance on cassava as it is drought tolerant, but it may also be due to an increase in cyanogenic glucosides. Episodic droughts are forecast to become more common in many cassava-growing regions. We therefore sought to quantify the effect of water-stress on both yield and cyanogenic glucoside concentration (CNc) in the developing tubers of cassava. Five-month-old plants were grown in a glasshouse and either well watered or droughted for 28 days. A subset of droughted plants was re-watered half way through the experiment. Droughted plants had 45% fewer leaves and lower tuber yield, by 83%, compared with well-watered plants. CNc was 2.9-fold higher in the young leaves of droughted plants, whereas CNc in tubers from droughted plants was 4-fold greater than in tubers from well-watered plants. Re-watered plants had a similar biomass to control plants, and lower CNc than droughted plants. These findings highlight the important link between food quality and episodic drought.

A considerable amount of the carbon fixed by plants is emitted back into the atmosphere as volatile organic compounds (VOCs). Novel inducible VOCs released from plants after biotic or abiotic stresses temporarily increase total emissions... more

A considerable amount of the carbon fixed by plants is emitted back into the atmosphere as volatile organic compounds (VOCs). Novel inducible VOCs released from plants after biotic or abiotic stresses temporarily increase total emissions of carbon substantially. As well as having a role in attracting the natural enemies of herbivores, inducible VOCs are also involved in plant-to-plant signalling, pathogen defence and ozone quenching, as well as tropospheric ozone and fine-particle aerosol formation. To relate these diverse observations to active plant defence, a conceptual framework of four functional levels (plant cellular interspace, leaf boundary layer, ecosystem and atmosphere) of inducible VOCs is proposed to aid understanding of the evolutionary role of inducible plant volatiles.

How species interactions may modify the effects of environmental change on evolutionary adaptation is poorly understood. Elevated CO2 is known to alter plant–herbivore interactions, but the evolutionary consequences for plant populations... more

How species interactions may modify the effects of environmental change on evolutionary adaptation is poorly understood. Elevated CO2 is known to alter plant–herbivore interactions, but the evolutionary consequences for plant populations have received little attention. We conducted an experiment to determine the effects of elevated CO2 and herbivory by a specialist insect herbivore (Danaus plexippus) on the expression of constitutive and induced plant defense traits in five genotypes of Asclepias syriaca, and assessed the heritability of these traits. We also examined changes in relative fitness among plant genotypes in response to altered CO2 and herbivory. The expression of plant defense traits varied significantly among genotypes. Elevated CO2 increased plant growth and physical defenses (toughness and latex), but decreased investment in chemical defenses (cardenolides). We found no effect of elevated CO2 on plant induction of cardenolides in response to caterpillar herbivory. Elevated CO2 decreased the expression of chemical defenses (cardenolides) to a different extent depending on plant genotype. Differential effects of CO2 on plant defense expression, rather than direct effects on relative fitness, may alter A. syriaca adaptation to changing climate.

Abstract Background: Cyanogenic glucosides are common bioactive products that break down to release toxic hydrogen cyanide (HCN) when combined with specific β-glucosidases. In forage sorghum, high concentrations of the cyanogenic... more

Popular in the urban environment is the horse chestnut, Aesculus hippocastanum which is suffering mainly due to the feeding of the horse chestnut leaf miner (Cameraria ohridella). The harmfulness of this pest is well recognized. Not much... more

Popular in the urban environment is the horse chestnut, Aesculus hippocastanum which is suffering mainly due to the feeding of the horse chestnut leaf miner (Cameraria ohridella). The harmfulness of this pest is well recognized. Not much attention was put in discovering the interaction of this insect with the fungal pathogen Guignardia aesuli, the agent of leaf blotch. Host plant mediation in this particular insect-plant pathogen interaction is crucial for understanding the complexity of the horse chestnut's current and future situation. Recognising the response of the host plant for separated and simultaneous colonisation by insect and fungus was the aim of this study. Leaf damage dynamics and phenolic compounds content (total soluble phenolic compounds – TPh, and condensed tannins – CT), and stem volume increment (SVI) of the horse chestnut saplings was considered and their relationship identified. The main hypothesis was that insect feeding and fungal infection when separated elicit a similar pattern in defence response of the host but this defence response is different when they both coexist on the same plant. Basing on crown projection area photographs sequence, foliage damage dynamics was assessed (Richard's growth model) and protocol developed. Measurements of stem volume were performed sequentially to indicate potential growth response. Through this study, it was identified that the content of phenolic compounds in leaves was higher when both pests colonized saplings in comparison with those where saplings were infested by one biotic factor. It is also documented that foliage damage dynamics was higher when only the fungal pathogen attacked plants than when it was infected by both pests. A trade-off was identified between growth and secondary metabolism. Leaf damage affected stem volume increment only in the late summer, when a high level of defoliation was observed. Simultaneous infestation by fungal and insect agents made unfavourable conditions rather for the former. How this interaction affects the latter is not covered by our results and still remains undiscovered.