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• W149037548 abstract "Water loss of soybean leaf area remaining was mea sured on artificially and insect-defoliated leaves to define possible differences in water loss between defoliation methods. Water loss es of punched defoliated leaves (inflicted with a paper punch) were significantly greater than those of picked defoliated leaves (inflicted by excising leaflets) at comparable percentages of defoliation. Sim ilarities in water loss and trends of water loss through time between punch-defoliated and insect-defoliated leaves suggested that punching leaves more accurately simulated damage from insects than did picking leaves. Damage-simulation studies have been conducted on soybeans to deter mine yield-loss relationships from various sources of defoliation (e.g., hail, leaf diseases, and insects). Hail damage has been simulated by mechanically shredding leaves and breaking stems to achieve light, medium, and heavy damage (Kalton et al., 1949), manually throwing cracked ice (Neill, 1952), and removal of leaves to attain desired percentages of defoliation (Kalton et al., 1949; Camery and Weber, 1953; Teigen and Vorst, 1975). Removal of leaves consisted of excising leaves and leaflets and/or cutting off the terminal portions of leaflets. Simulation of pathogen-induced defoliation has been conducted by removal of entire leaves (Lockwood et al., 1977). Insect damage has been simulated most often by methods similar to those used in hail-damage studies. Defoliations have been inflicted by excising leaves or leaflets (Todd and Morgan, 1972, Thomas et al., 1974) and by a combination of excising and/or cutting off portions of leaflets (Turnipseed, 1972). Poston and Pedigo (1976) simulated insect-defoliation, however, by punching holes in leaves with a paper punch or cork borer to remove per centages of total area. They reasoned that tattering produced by punching holes better simulated the tattering produced by insect feeding. 1 Journal Paper No. J-9470 of the Iowa Agriculture and Home Economics Experiment Sta tion, Ames, Iowa. Project No. 2248. 2 Presently Assistant Professor of Entomology, Ohio Agricultural Research and Development Center, Wooster 44691. 3 Professor of Entomology. Received for publication 28 February 1980. This content downloaded from 157.55.39.231 on Thu, 06 Oct 2016 04:18:35 UTC All use subject to http://about.jstor.org/terms 332 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY Differences between some of these defoliation methods have been re ported in the literature. Poston et al. (1976) found that across-the-midrib leaflet bisections increased soybean net photosynthesis of remaining leaf tissue and that it did not simulate defoliation by insects. Cork borers, paper punches, and along-the-midrib bisections simulated insect defoliation based on net photosynthesis. Working with another crop, cotton, Davidson (1973) showed that leaf punching caused a greater reduction in yield than simply removing an equivalent amount of leaf tissue at the petiole. Parameters other than photosynthesis and crop yield also may be affected differentially by defoliation methods. In a study of drought resistance with soybeans, Clark and Levitt (1956) showed that water loss was greater when soybean leaves were than when left uncut. Because punching holes in leaves produces a cut leaf, as contrasted to picking leaves which allows the leaf to remain uncut, there is a distinct possibility that differences in water loss between these defoliation methods may exist. Therefore, this study was conducted to evaluate water losses, if any, between types of artificial and natural defoliation. Methods and Materials Seven defoliation treatments were compared: 0% defoliation (check), 33% and 66% defoliation inflicted by punching holes in leaves, 33% and 66% defoliation inflicted by excising leaflets (66% defoliation included 1 treat ment with the terminal leaflet remaining, and 1 treatment with a lateral leaflet remaining), and natural insect defoliation represented by the green cloverworm (GCW), Plathypena scabra (F.). In the greenhouse, soil flats (40 x 55 cm) were planted with 32 soybean seeds (var. 'Amsoy 7T) spaced equidistantly. When soybeans reached plant-growth stage V4 (Fehr et al., 1971), defoliation treatments were ini tiated. Soil flats containing soybeans were placed separately into screened cages (60 cm3) to insure comparable light intensities on all flats during the defoliation period. GCW larvae (4th-6th stage), from a greenhouse colony, then were placed on soybeans in a randomly-chosen cage. Larvae were placed in the cage in numbers sufficient (>60) to insure that medium to heavy defoliation occurred in a 24-h feeding period. At this time, other cages were randomly assigned a defoliation treatment, and treatments then were replicated 15 times. Punched-leaf defoliations were accomplished by removing the necessary percentage of leaf tissue with a paper punch. Selected leaves were measured before defoliation with a LiCor? area meter and subsequently defoliated on a percentage basis. Picked-leaf defoliations were accomplished by excising 1 lateral leaflet/leaf for 33% defoliation and 2 leaflets/leaf for 66% defoliation. To insure uni formity between leaves, only 2nd trifoliate leaves (3rd node) were chosen to be defoliated. This content downloaded from 157.55.39.231 on Thu, 06 Oct 2016 04:18:35 UTC All use subject to http://about.jstor.org/terms VOLUME 54, NUMBER 2 333 After the 24-h insect-feeding period, GCW larvae were removed from the cage with insect-defoliated plants; then, all soybean flats were removed from their cages. Eleven, 14 or 12 leaves (in trials 1, 2, or 3, respectively) were excised from each flat and placed into florist aquapics, which were filled with a predetermined volume of water. Number of leaves excised in each trial was determined by the number of leaves with adequate defoliation in the insect-defoliated cage. In trials 1, 2, and 3, this was 11, 14 and 12 leaves respectively. Aquapics then were arranged spatially according to a random ized complete-block design, each with the 7 treatments. Leaves were mea sured with the area meter to determine their leaf areas after defoliation. Leaves were held in the laboratory with environmental conditions of ca. 23.9? C, 30-45% RH, and a photophase set at 15-h. During a 10-day period, water loss from the aquapics was measured at 24-h intervals by recording the volume of water necessary to return the water level to the predetermined mark. When leaves dried or began to yellow, they were removed, and water loss was no longer measured. Results and Discussion To compensate for significant differences in leaf area (after defoliation) between treatments (Table 1), water loss is presented as ml of water lost per cm2 of leaf area. Thus, effects of defoliation methods on water loss can be directly compared. Table 1 also presents water losses obtained in each trial for all treatments. Analysis of variance was used to test for significant differences (P = 0.05) among treatments in leaf area and water loss. Water losses of punched 33 and 66% leaves were significantly greater than those of picked 33 and 66% (terminal or lateral leaflet) leaves, respectively, in each of the 3 trials. Water loss of insect-defoliated leaves was not signif icantly different from those of punched 33% leaves and picked 66% leaves (lateral leaflet) in trials 1 and 2, and of punched 66% leaves in trial 3. Insect defoliated leaves in trial 3 had a water loss significantly greater than that of punched 33% leaves and all picked leaves. In trials 1 and 2, all defoliation treatments had a water loss significantly greater than the check, but in trial 3, only the punched-, and insect-defoliation treatments were significantly greater. Increases in percentages of defoliation usually were accompanied by in creases in water loss per leaf area remaining of both punched and picked leaves. Water losses of punched 66% leaves were significantly greater than those of punched 33% leaves in all 3 trials, but picked 66% leaves (terminal and lateral leaflets) had water losses significantly greater than picked 33% leaves only in trials 1 and 2. A 2nd statistical technique used to analyze effects of defoliation method on water loss was to examine trends in water loss through time (days). This content downloaded from 157.55.39.231 on Thu, 06 Oct 2016 04:18:35 UTC All use subject to http://about.jstor.org/terms Table 1. Average leaf area (cm2) after defoliation, percent reduction in leaf area from the check, and average water loss (ml H20/cm2 leaf area) per day for each leaf. _ 5 1 2 3 _ _,_ _ _ 73 Defoliation treatment % Reduction Water loss % Reduction Water loss % Reduction Water loss Z Leaf area in leaf area (ml H20/cm2 Leaf area in leaf area (ml H20/cm2 Leaf area in leaf area (ml H20/cm2 ^ Method % (cm2) rom check leaf area)/day (cm2) from check leaf area)/day (cm2) from check leaf area) day ^ o Insect Variable 22.99 d 48.4 5.10 b 29.99 c 47.4 4.46 b 32.68 c 46.0 5.88 a ^ Punch 33 34.47 b 22.9 4.63 be 32.51c 43.0 4.46 b 38.32 b 36.6 4.57 b E Punch 66 23.45 d 47.4 6.10 a 18.58 d 67.4 6.66 a 24.98 de 58.7 6.07 a m Pick 33 30.04 c 32.6 3.27 d 37.37 b 34.5 3.18 d 42.85 b 29.2 2.68 c ? Pick-Tb 66 21.10 d 52.7 4.16 c 19.87 d 65.1 3.93 c 26.14 d 56.8 3.19 c Z Pick-Lb 66 13.14 e 70.5 4.63 be 19.65 d 65.5 4.36 be 21.00 e 65.3 3.36 c > Check ? 44.59 a * 2.66 e 57.01 a * 2.34 e 60.48 a * 2.29 c ? ____________________________________________________^ CD z a Numbers followed by different letters are significantly different (P = 0.05) by Duncan's Multiple Range Test. H b T = Terminal leaflet remaining; L = Lateral leaflet remaining. g O r o o n > r" @default.
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• W149037548 title "Effects of Artificial and Insect Defoliation on Water Loss from Excised Soybean Leaves" @default.
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