Insect resis

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Breeding for Arthropod (insects and mites) Resistance in Plants Total average yield loss in U.S. to pests about 36% (12% each to pathogens, insects, and weeds) Culture and training Chemical pesticides Integrated pest management

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Breeding for Arthropod Resistance in Plants Many similarities between breeding for disease and insect resistance – differences in terminology; greater emphasis on mechanisms of resistance; main difference is the mobility of insects Problem with breeding techniques (insect controlled nurseries) – deliberate selection for insect resistance not common; (insect general resistance erosion?)

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History Grape phylloxera (1860 – present day) French wine production fell 70% between 1863-1875 Both insect and source of resistance from NA

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Mechanisms of Resistance 3 categories – Originated with R. H. Painter (1) Nonpreference (Antixenosis) – Complex of plant characteristics which prevent insects from approaching, landing, settling, feeding or ovipositing; it affects the behavior of the insects (altered number of insects landing or number laying eggs); has been termed non-acceptance (Allelo)chemical nonpreference: volatile (released into air and sensed by insect before they land) or sensed or tasted by insect after contact or during feeding: Examples: Raspberry aphid; Sugarbeet aphid; Rice brown planthopper Morphological nonpreference: leaf hairiness, stem hardness: cereal leaf beetle; wheat stem sawfly

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Raspberry aphid damage by Amphorophora ideai 11 Major genes for resistance Resistance identified by aphids walking off leaves (antixenosis)

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Sugarbeet aphid resistance Four genes identified for resistance to aphid settling (anitxenosis)

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Rice brown planthopper resistance Resistance based on the absence of asparagine production (antixenosis)

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Cereal leaf beetle Morphological non-preference

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Wheat stem sawfly life cycle

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Wheat stem sawfly Morphological non-preference

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Mechanisms of Resistance (2) Antibiosis – Defensive compounds which affects the reproduction of insects; interferes with longevity, oviposition rate, generation time, and preadult mortality; it affects insect's physiology. reduce insect growth, inhibit reproduction, alter physiology, delay maturity; European corn borer resistance in corn (DIMBOA, cyclic hydroxamic acid); greenbug resistance in barley (benzyl alcohol concentration)

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European corn borer damage Resistance in leaves due to inhibition of larval growth by cyclic hydroxamic acid (DIMBOA) (antibiosis)

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Greenbug resistance in barley Damage caused by toxin secretion into leaves; resistance due to benzyl alcohol concentration (antibiosis)

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Mechanisms of Resistance (3) Tolerance – Complex of plant characteristics which allow the plant to endure some amount of insect attack without affecting yield or quality. Has no effect on the insect population (no selection pressure)

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Resistance Mechanism Pest Resistance breaking biotype Leaf Pubescence Cereal leaf beetle No Jassids No Stem borers No Solid stems Wheat stem sawfly No High silica content Rice stem borers No Nutritional deficiencies Rice planthoppers Yes Chemical antibiosis factors gossypol Cotton pests No benzyl alcohol Cereal greenbugs Yes DIMBOA Euro corn borer No Unknown factors Hessian fly Yes Raspberry aphid Yes

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Klingler et al., 2005. Aphid Resistance in Medicago truncatula Involves Antixenosis and Phloem-Specific, Inducible Antibiosis, and Maps to a Single Locus Flanked by NBS-LRR Resistance Gene Analogs. Plant Physiology 137:1445-1455. M. truncatula – barrel medic, annual pasture legume bluegreen aphid

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Resistance in 'Jester' due to non-preference (non-settling) in both field and greenhouse experiments

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Resistance in 'Jester' due to antibiosis (reduced aphid survival and reduced population growth rate

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Segregation ratios strongly support a single, dominant gene controlling bluegreen aphid resistance in 'Jester'. Mapped locus to region flanked by resistance gene analogs predicted to encode the CC-NBS-LRR subfamily of resistance proteins.

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