water stress - insects

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Information about water stress - insects
Science-Technology

Published on February 12, 2009

Author: aSGuest12908

Source: authorstream.com

WATER STRESS OF CROPS -INSECT AND DISEASE INCIDENCE : WATER STRESS OF CROPS -INSECT AND DISEASE INCIDENCE Course teachers : Dr. NANDHINI Dr. GIRIJA Presented by : S.SAMBATH KUMAR 2008-11-118 Stress : Stress Any external constraint - reduces the ability of a plant to develop to its genetically predetermined level Plant species are highly variable in their optimum environments Slide 3: Water stress avoidance: Deep root systems Thick cuticles Fleshy leaves Slide 4: Stress Tolerance: Requires the plant to come to thermodynamic equilibrium with the stress Internal conditions are in equilibrium with conditions outside of the plant E.g., Plant can survive the desiccation of the protoplasm without injury. It also has the ability to rehydrate the protoplasm without injury and retaining the ability to resume normal growth upon rehydration of the protoplasm Slide 5: Adaption: Heritable modifications in structure or function which increase the fitness of the plant in a stressful environment E.g. The morphological and physiological adaptations of CAM plants Slide 6: Acclimation: Non-inheritable adaptations that occur over the lifespan of a plant Modifications are induced upon gradual exposure to the stress - genetic trait Lack of water stimulates : Lack of water stimulates Production of abscisic acid Early stomatal closure Inhibit the production of new leaves Increase cuticle thickness Initiation of leaf abscission Slide 8: Loss of turgidity Change in cell volume Increase intra cellular solutes Protein denaturation Disruption of membrane integrity Change In gene expression & metabolism MECHANISMS : Plant stress responses : MECHANISMS : Plant stress responses Stress recognition Signal transduction Gene expression Altered cell metabolism Physiological and developmental response Response of insects : Response of insects Insect attack : Insect attack Generally, the insect damage to several plants which are all already subjected to water stress were significantly lower than the plants were grown in the absence of water stress Insects attacking the plants when they are under stress : Insects attacking the plants when they are under stress Mites Jassids Thrips Beetles Pod bugs White flies Leaf webber Factors attracting insects during crop stress : Factors attracting insects during crop stress Low osmotic potential Accumulation of more nutrients Easy stylet penetration Non prefering Plant characters of insects : Non prefering Plant characters of insects Tough foliage Less nutrient content Less palatableness Low moisture content – e.g. silk worm Plant factors: : Plant factors: Direct effects: 1. Affecting plant metabolism, which affects pests nutrition on hosts 2. Modifying the microclimate through changes in habit, growth density, etc. Slide 16: Effects on pest establishment and spreading within the plant: 1. Alteration of plant structure 2. Stomata function - Affecting plant's ability to recover from pest attack, through the repair of damage Slide 17: Indirect effects: Pest population, development, multiplication, survival, vigour, life-cycle length, etc… Plant nutrition influences insect responses : Plant nutrition influences insect responses Influencing the amount of suitable plant nutrients Silicon (Si) can improve resistance of plants to insect attack and may also enhance tolerance of water stress Inhibitory compounds or anti-quality factors Attractant compounds Tolerance to herbivory Effects on predators and parasitoids Plant effects on insects : Plant effects on insects Influence the proportion of migratory insects The fecundity of the colonizers The viability of eggs and larvae The rate of insect development The ability of natural enemies to influence insect populations Herbivore influence on subsequent water stress : Herbivore influence on subsequent water stress Removal of leaf area reduce the water use by plants Partially chewed leaves having greater exposure of desiccating area Root feeding nematodes also can induce water stress Plant under water stress means: : Plant under water stress means: Plants have many defense mechanisms: Physical barriers - waxes (cuticle), trichomes Chemical - toxins, feeding deterrents, secondary metabolites Volatiles - Communicate with other plants Get help from others - attract predatory insects; support stinging ants e.g. Acacia tree Slide 22: The beet armyworm, Spodoptera exigua , shown feeding on the model legume species Medicago truncatula; the first fatty-acid : amino-acid conjugates (FACs) to be identified as elicitors of plant defense Slide 23: ABA-deficient plants had reduced resistance to the insect - Spodoptera exigua (cut worm) ABA-deficient plants had higher resistant to bacterial speck disease, consistent with the proposed role of salicylate in defense against pathogens Essential effects: Slide 24: Phytophagous sap-feeders, are adversely affected by continuous water stress. Phloem feeding insects respond positively on intermittently stressed plants but exhibit poor performance on continuously stressed ones Strong negative effects of water stress on the performance of sap-feeding insect and on members of the phloem- and mesophyll-feeding insects. Response of diseases : Response of diseases Diseases resonse to plants when they are under stress : Diseases resonse to plants when they are under stress Charcoal rot Powdery mildew Dry root rot Ergot Leaf spot Slide 27: Maize plants are subjected to post-flowering water stress are more susceptible to dry root rot attack. Colonization of roots and charcoal rot development occur only when plants are drought stressed during reproductive growth Examples: Slide 28: Insect defoliation seems to promote fungal colonization under moderate water stress Severity of Smut disease is higher on maize plants stressed at Grain filling than at Vegetative, Tasseling or Silking stages Salicylic acid, jasmonic acid, oligo -saccharides important role in plant defense against pathogen Slide 29: Foliar polycyclic diseases : It often less common and less severe during drought episodes: Rain / moisture needed for dissemination, germination and penetration) Stem and root diseases : Indirect effects through host physiology : water stress is determinant Slide 30: 1. Effects of water stress on host –pathogen interaction : increases susceptibility to pathogens:PREDISPOSITION Types of pathogens: mainly necrotrophs, facultative parasites E H P 1. Predisposition of trees to disease by water stress : 1. Predisposition of trees to disease by water stress Water stress - enhanced diseases  : It is favoured by water stress but caused by « true parasites » mainly cankers (necrotroph pathogens) e.g: Sphaeropsis sapinea Slide 32: Waer stress - induced diseases : It caused by opportunistic, facultative or conditional parasites. mainly by endophytic species e.g. Biscognauxia mediterranea Mechanisms of predisposition : Mechanisms of predisposition Decrease in photosynthetic activity Alternation of protein synthesis in dehydrated plants Metabolic changes : improved substrate for pathogen (nitrogen) Decreased defensive compounds (phytoalexins, enzymes, etc…) Slowed defenses limiting compartmentalization Slide 34: Main symptoms associated with water stress S. sapinea Bark necrosis Canker (uncommon in Europe) Crown or branch dieback Slide 35: Biscogniauxia (Hypoxylon) mediterraneum : - an endophyte turning to parasite with water stress Predisposition, Combination of biotic and abiotic stresses : Predisposition, Combination of biotic and abiotic stresses Both infection and water strss act on the plant together In general, this results in additive or synergistic deleterious effects Combined effects of infection and water stresses1. Root pathogen (affecting directly water relations)Ex : Collybia fusipes, root pathogen on oak (Marçais) : Combined effects of infection and water stresses1. Root pathogen (affecting directly water relations)Ex : Collybia fusipes, root pathogen on oak (Marçais) Slide 38:  e.g.oaks growing in high sand content are not more susceptible to Collybia) Slide 39: 2. Foliar pathogen (Ground nut rust) (affecting the photosynthesis) Water stress prevents the growth of new, uninfected leaves Effects of stresses in plant populations and communities : Effects of stresses in plant populations and communities Water stress and infection can have additive effects in increasing both inter- and intra- specific competitive fitness Competition for resources Water stress DISEASE Fitness Nematode : Nematode Reduced fecundity Increase or decrease in population Sedentry nature Host plant attachment Low infestation eg. Rotylenchus, Pratylenchus Future prospects : Future prospects Considerations for management Measures aimed at limiting pathogen, Insect spread : Promote some silvicultural practices that promote elastic responses of stands to water Prevention of biotype development Slide 44: Thank you

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