Biotic Stress and Yield Loss

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plays a key role in promoting plant fitness. Plants that have compensatory responsemechanisms have a fitness advantage in the presence of severe herbivore injury.Compensatory response may have evolved in response to the selection pressure byherbivores, although some suggest that it could have also evolved in response to plantcompetition. 55 Regardless, compensatory response is a desirable plant trait both innatural and agricultural ecosystems.Plant tolerance to insect injury is an inherited trait. Generally, tolerant cultivarshave a rapid growth rate and recover from insect injury 56–58 without significant yieldloss. Although tolerance is genetically controlled, its expression may be confoundedby environmental factors. If appropriate growing conditions are not met, plant tolerancemay not be expressed.Availability of moisture and nutrients in the soil affects the source-sink relationshipsin plants, directly impacting plant compensation to arthropod injury. Bloom etal. 59 suggested that plants allocate resources to new biomass to acquire resources thatare in short supply and potentially limit plant growth. For instance, plants growing insoils deficient with moisture would have to allocate more resources to roots to absorbmore moisture. Because most of the photosynthates are directed to roots, such plantswould be susceptible to injury by defoliating herbivores because there are limitedphotosynthates to replace defoliated leaves. Therefore, plants with limited resourcesare more susceptible to arthropod injury compared to plants with an optimum supplyof resources. Likewise, plants adapted to growing in suboptimal environments have60, 61a slow growth rate and are less able to replace tissues lost to herbivory.Consequently, such plants tend to deploy active chemical defenses to deter generalistherbivores.Plant compensation to herbivore injury depends on the level of injury, plant phenologywhen injury occurs, plant parts injured, and also the resources available forgrowth and development of plants. Because plant compensation to insect injurydepends on the plant growth rate, optimal resource supply can directly influence thelevel of compensation plants exhibit. Moisture stress modifies plant tolerance toinsect injury. Assuming that all other resources for plant growth and development aremet, provision of optimum soil moisture can increase plant tolerance to insect injury.For example, although significant defoliation was imposed, soybeans grown in a yearwith ample rainfall replaced leaf tissue lost by defoliation in 11 days to attain a criticalleaf area index of 3.5. Ample moisture supply initiated rapid soybean growth,delayed maturity, and delayed senescence with sustained photosynthesis. However,during a year with suboptimal moisture, there was no canopy recovery and defoliationcaused significant yield reduction.62, 638.7 METABOLIC COSTS TO MAINTAIN PLANTCOMPENSATION AND MEDIATIONBY MOISTURECompensatory growth of plants to arthropod injury usually occurs in environmentsrich with resources required for plant growth and development. 64 Plant compensation
to herbivory depends on the plant’s primary metabolism, and it seems that there arelimited or no metabolic costs associated with compensation if resources are availableto plants in sufficient amount. In contrast, chemical defense against herbivores ismore strongly developed in plant species that are adapted to low resource environments,including drought conditions. 60, 65 Chemical plant defense usually requiresadditional metabolic pathways to produce a compound used for defense. Therefore,chemical defense is considered more expensive than compensatory growth.Regarding metabolic costs involved in tolerance, ecological studies suggest thatcompensatory growth is not costly if plants are grown in resource-rich environments,such as optimal water supply. Some ecologists argue that herbivory is advantageousand leads to overcompensation. 66, 67 However, in agroecosystems, available evidencesuggests that compensatory growth is costly. For example, the high level of tolerancein wild tomatoes was a trade-off for less yield compared to cultivated tomatoes thatare less defoliation tolerant but high yielding. 68 A tolerant barley cultivar supportedequal greenbug population density as did the susceptible cultivar, but gave highergrain yield. But in the absence of greenbug infestation, the tolerant barley cultivaryielded lower than the susceptible cultivar, thus demonstrating a yield-drag associatedwith plant tolerance. 69Plants deploying compensatory growth as a defense strategy generally have arapid growth rate and allocate resources to leaves and roots for more resource acquisition.61 In suboptimal environments, plants would not exhibit a compensatoryresponse. It may be inaccurate to generalize that plants under natural conditions docompensate for herbivory but not plants in agricultural systems. If resources are sufficientlyprovided, plants in an agricultural system also could exhibit some level ofcompensatory growth to herbivory. This has been demonstrated with compensatoryregrowth of soybean to defoliation when moisture and nutrient were in optimum supply.62, 63 Consequently, the answer to the question of whether compensatory growthis costly to the plant, like chemical or structural defenses, should be considered withcaution. It seems that all defenses are costly, including compensatory growth. In compensatorygrowth, it is costly because plants need an adequate supply of resources toexhibit compensatory responses. In an agricultural ecosystem, provision of adequateresources to increase the level of plant compensation to arthropod injury may entailcosts associated with farming inputs, for instance, costs for irrigation water whereprecipitation is marginal.8.8 INTERACTION OF DROUGHT STRESS, INSECTINJURY, AND PLANT YIELD LOSSMoisture stress reduces photosynthetic rates, plant biomass, and yield. 70–72Moisture-stressed plants have smaller canopies, are more susceptible to insect injury,and suffer heavier yield loss compared to unstressed plants. Consequently, the economicinjury levels of drought-stressed soybeans were different from those that werenot drought-stressed. 73, 74 These studies showed that drought-stressed soybeans hadlower economic injury levels compared to drought-unstressed soybeans.
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Biotic Stressand Yield Loss
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Library of Congress Cataloging-in-P
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PrefaceThe idea for this book came
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EditorsRobert K. D. Peterson, Ph.D.
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ContentsChapter 1Illuminating the B
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1Illuminating the Black Box:The Rel
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increase plant tolerance, through p
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the action of a stressor on a plant
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The magnitude and duration of injur
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Plant part injuredrefers to the pla
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cific competition, while agricultur
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2Yield Loss and PestManagementLeon
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direct relationships between the ac
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In keeping with the theme of this b
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egressions. Actually, the title “
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REFERENCES1. Teng, P. S., Crop Loss
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3Techniques for EvaluatingYield Los
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number of species and stage of cutw
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especially if buried in soil, can d
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elationships for some pests. When m
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injury can be precisely controlled
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day. 81, 99 However, except for an
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the literature most likely are actu
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20. Ba-Angood, S. A., and Stewart,
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60. Stewart, J. G., McRae, K. B., a
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99. Shields, E. J., and Wyman, J. A
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4.3.3.1.3 Third generation European
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ing on the developmental stage at t
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4.2.2.1.2 Temperature stressPlant s
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chronic injury. Acute injury result
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ows, roadsides, or small grain fiel
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numbers are present. Stink bugs, Eu
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Oligonychus pratensis, feed on corn
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ECB2. 224.3.3.1.4 The impacts of Eu
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stalk borer, Papaipema nebris, is a
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period prolonged with sufficient co
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Arthropod injuries to developing ea
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esponses to herbivory have been obs
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Midwest, Purdue University CES and
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59. Bailey, W. C., and Pedigo, L. P
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5Phenological Disruptionand Yield L
Page 84 and 85: ity by animal consumers is the agro
Page 86 and 87: ously, structural components (e.g.,
Page 88 and 89: FIGURE 5.2 Generalized alfalfa grow
Page 90 and 91: 601, 1972.9. Gordon, C. H., Derbysh
Page 92 and 93: do we know about how biotic stresso
Page 94 and 95: ing both large and small leaf veins
Page 96 and 97: population. Whole plants may respon
Page 98 and 99: temporally and spatially, are more
Page 100 and 101: some systems have allowed for a tra
Page 102 and 103: injury guilds would center on the f
Page 104 and 105: apple leaves, HortScience, 19, 815,
Page 106 and 107: 7The Influence of Cultivarand Plant
Page 108 and 109: unit ground area, and it indicates
Page 110 and 111: without considering plant architect
Page 112 and 113: photosynthesis. Regardless of the n
Page 114 and 115: light interception. 45 Skeletonizin
Page 116 and 117: Light interception, which intrinsic
Page 118 and 119: var. Consequently, use of a single
Page 120 and 121: 19. Jarosik, V., Phytoseiulus persi
Page 122 and 123: 62. Caviness, C. E., Registration o
Page 124 and 125: 8Drought Stress, Insects,and Yield
Page 126 and 127: humidity. Because the relative humi
Page 128 and 129: temperature and precipitation. Prop
Page 130 and 131: compared to well watered soybeans.
Page 132 and 133: Changes in plant hormones, such as
Page 136 and 137: In soybeans, a leaf area index (LAI
Page 138 and 139: 15. Schulze, E. D., Water and nutri
Page 140 and 141: 52. Meyer W. S., and Walker, S., Le
Page 142 and 143: 9The Impact of Herbivoryon Plants:
Page 144 and 145: conditions of stress are themselves
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Page 148 and 149: plant tissue, resulting in gall for
Page 150 and 151: found on cucumbers in polycultures
Page 152 and 153: compensatory response. Also, more v
Page 154 and 155: Costa Rica, and there are several g
Page 156 and 157: ivory from white cabbage butterfly
Page 158 and 159: made, while larger vertebrate herbi
Page 160 and 161: important consequences to plant fit
Page 162 and 163: de Entomol., 38, 421, 1994.32. Kare
Page 164 and 165: chlorophyll content in spider mite
Page 166 and 167: 114. Karban, R., and Strauss, S.Y.,
Page 168 and 169: 10Stephen C. WelterCONTENTSContrast
Page 170 and 171: Although literature is drawn from a
Page 172 and 173: and wheat acres receiving some type
Page 174 and 175: pattern to be true. 109 Because rel
Page 176 and 177: used in the experiment influenced t
Page 178 and 179: artificially elevated nitrogen leve
Page 180 and 181: annual, landrace cultivars, or mode
Page 182 and 183: settings are coupled with genotype
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10. Kennedy, G. G., and Barbour, J.
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53. Panda, N., and Heinrichs, E. A.
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97. Gross, K. L., and Soule, J. D.,
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143. Davidson, J. L., and Milthorpe
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11Crop Disease andYield LossBrian D
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The conditions listed above are opt
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to associate the effects of disease
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general relationship between LAI an
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Biomassproduction(total dryweight)R
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Y RUE(t)RI(t)[1 X]dt [11.12]wher
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sue. The most accurate prediction o
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tion. Two weeks before harvest, the
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15. Spitters, C. J. T., Van Roermun
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57. Richardson, A. J., Wiegand, C.
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they were cheap, convenient, and ef
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dW / W dtcauses and consequences of
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(a)(b)Maize yield (Mg ha -1 )987654
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Recall that c is a constant, so by
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where the subscripts c and w repres
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0.6Fraction yield loss0.40.2Eq. 16,
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the leaf area index (LAI). Incorpor
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can no longer be tolerated and, the
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cide. Steckel et al. 68 showed that
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A eq ∑ jN eq,ji 1YL n,j [12.31]1
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samples per field. Thomas 85 sugges
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external factors such as annual wea
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38. Boznic, A. C., and Swanton, C.
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weeds, Weed Sci., 44, 856, 1996.79.
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competition and weed management. 3-
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per unit biomass (1/W i)(dW i/dt) o
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of light interception). Algorithms
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where G a,iis the water limited pla
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13.4 COMPETITION FOR SOIL NITROGENA
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As with soil water, Equations 13.10
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partitioning of nitrogen to leaves.
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and stems to optimize photosyntheti
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influence of enhanced UV-B conditio
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Systems Approaches at the Field Lev
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