PHOTOSYNTHESIS RESPONSE OF ‘CAROLINA’ CUCUMBER TO SIMULATED AND ACTUAL STRIPED CUCUMBER BEETLE (COLEOPTERA: CHRYSOMELI-DAE) DEFOLIATION*

Abstract Field studies were conducted in 1995 to compare the photosynthesis response between simulated striped cucumber beetle, Acalymma vittatum (F.), defoliation and actual A. vittatum defoliation in ‘Carolina’ cucumber. Six simulated defoliation levels (0%–100%)were used over 5 timings of defoliation (first true leaf to harvest). Plots were defoliated with scissors twice each week throughout each timing interval, and defined as continuous defoliation. In addition to continuous defoliation, one-time simulated defoliation treatments were imposed using the same timing treatments but only 4 defoliation levels (0, 25, 50, and 100%). Two cage studies, with A. vittatum adults, were used to provide estimates of actual insect defoliation injury. Beetles were placed in cages for 2 weeks at densities of 0, 1, 3, 5, and 10/plant and net photosynthetic rates were measured. No significant differences (P <0. ⁰⁵ were detected in pho-tosynthetic rates between simulated and actual insect defoliation treatments. Also, few significant differences in photosynthetic rates were detected between damaged and undamaged leaves in the simulated insect defoliation study. Results indicated that the simulated insect defoliation procedure appeared to accurately reflect the growth response of ‘Carolina’ cucumber subjected to actual A. vittatum defoliation, and that simulated defoliation results should be appropriate for developing economic injury levels for A. vittatum on cucumber.     

Artificial injury experiments on the damaging effect of Leucoptera malifoliella on apple trees

In 1986 and 1987 defoliation experiments on the apple cultivar Herma were performed to simulate the occurrence of Leucoptera malifoliella Costa. Those model experiments were based on investigations on the mine size of Leucoptera malifoliella and yield loss on infested and tagged trees. Defoliation carried out by hand showed that heavy leaf loss reduced fruit number. Insufficient nutrient supply due to reduced leaf area and a consequently smaller leaf-fruit ratio led to a decrease in mean fruit size and total yield. Heavy leaf loss had also an adverse effect on fruit quality components (dry matter substance, viscosity, total sugar and acid content of fruit juice). This was finally reflected in sensory evaluation criteria. Heavy leaf losses also influenced blossom bud differentiation in the blossom set of the following year. Both number of inflorescences and number of blossoms per inflorescence were reduced. The evaluation of the extent of damage of L. malifoliella was based on previous investigations on reduced leaf area. For L. malifoliella a mean mine size of 0.96 cm² was found. This corresponds to a 4.2% loss of leaf area.The leaf-fruit ratio is of special importance for the evaluation of the extent of damage of leaf-damaging pests and was used to derive injury threshold ranges for L. malifoliella. Previous investigations on L. malifoliella infestations and the results from the artificial defoliation experiments enabled the determination of preliminary flexible injury thresholds. Depending on leaf-fruit ratio, yield level, and leaf miner generation, the thresholds vary between 0.1–2.5 eggs and mines per leaf.     

Host range of the European leaf sheath mining midge,Lasioptera donacis Coutin (Diptera: Cecidomyiidae), a biological control of giant reed,Arundo donax L.

The fundamental host range of the arundo leafminer, Lasioptera donacis a candidate agent for the invasive weed, Arundo donax was evaluated. L. donacis collects and inserts spores of a saprophytic fungus, Arthrinium arundinis, during oviposition. Larvae feed and develop in the decomposing leaf sheath channel tissue. Thirty-six closely related and economic grass species along with several key habitat associates were evaluated in no-choice tests. L. donacis and its associated saprophyte completed development only on A. donax, in concurrence with published reports from its native range in Mediterranean Europe. The arundo leafminer feeding leads to premature defoliation, constituting a different mode of attack on the host plant as compared to two previously released insects, the arundo wasp and arundo scale, which feed on shoot tips and rhizomes, respectively. Defoliation of A. donax is expected to increase light penetration into stands of A. donax which increases visibility for law enforcement, reduces the survival of cattle fever ticks, and enhance recovery of the native riparian vegetation along the Rio Grande and other habitats where this weed is invasive.     

Responses to defoliation of species-rich and monospecific tropical plant communities

Summary Floristically rich and monospecific tropical plant communities both responded to partial defoliation with increases in rates of production of new leaf area. Even after 50% of the leaf area had been removed three times, the leaf area increments were still higher in defoliated plots than in controls. Mean leaf area increment after defoliation, on a leaf area per unit ground area basis, was 905 cm² m^-2 d^-1 in diverse successional vegetation and 536 cm² m^-2 d^-1 in a cassava monoculture. Although defoliation stimulated leaf area development, on a per unit ground area basis, in both the cassava monoculture and the successional vegetation, the effect was more pronounced in the successional vegetation. On a per unit leaf area basis, leaf area increments following defoliation in both the diverse successional vegetation and the monoculture were approximately five times those of controls. The diverse plant community continued to respond vigorously after repeated defoliation, while the amount of stimulation of leaf are development in the monoculture declined. Because of their ability to respond even after repeated defoliation, diverse communities may in the long term be more homeostatic with respect to leaf area than are monocultures. The enhanced responsiveness of the species-rich community was due to changes in plant species abundance and very rapid leaf area development by some species.     

Temporal patterns of citrus greasy spot‐induced defoliation of sweet orange cultivars in Brazil

Recôncavo Baiano is an area favourable for the occurrence of citrus greasy spot (CGS) (Mycosphaerella citri), but there has been no study of this pathosystem in Brazil. This work aimed to characterise the temporal patterns of CGS‐induced defoliation in sweet orange cultivars ‘Bahia’ (Washington Navel) and ‘Pêra’. Temperature, rainfall and relative humidity were recorded, as well as weekly defoliation (fallen leaves/canopy m² or m³). Considering the mean of fallen leaves per canopy m², and mean canopy area, the total annual defoliation was estimated to be around 32 000 leaves per plant for ‘Bahia’ and 18 500 for ‘Pêra’ sweet orange. Spectral density analysis showed that defoliation has a 5‐week‐long main cycle for both cultivars. The proportion of symptomatic fallen leaves was never below 0.97. The monthly number of fallen leaves per canopy area was positively correlated with the mean CGS incidence on leaves. Defoliation was significant, resulting in a low leaf density throughout the year. Many defoliation cycles and the very high proportion of symptomatic fallen leaves assure a constant inoculum supply. Based on these results, CGS cannot be considered a minor disease, at least in Recôncavo Baiano.     

Early spring defoliation,secondary leaf flush,and leafminer outbreaks on American holly

Summary Adults of Phytomyza ilicicola (Diptera: Agromyzidae), a univoltine specialist leafminer, emerge in close synchrony with leaf flush of American holly and feed on and oviposit in soft, partially expanded leaves. Early spring defoliation, such as commonly results from freezing injury to young shoots, is followed several weeks later by a second flush of young leaves from lateral buds. We simulated this phenomenon by manually defoliating whole small trees and individual shoots of large trees to test the hypothesis that freezing injury can encourage leafminer outbreaks by inducing an abundance of soft, protein rich young leaves late in the adult activity period, when availability of vulnerable leaves becomes limited. Defoliation of small trees one or two weeks after bud break resulted in six- to 13-fold increases in the incidence of feeding punctures and larval mines on second flush leaves as compared with densities on original young leaves of control trees. Similarly, we induced significant increases in feeding punctures and larval mines on second flush leaves of individual defoliated shoots, although leaves that did not open until after the flight period escaped this injury. These observations underscore the capability of adult female P. ilicicola to locate and exploit a small number of phenologically available leaves among many hundreds of older leaves on the same tree. By altering the phenology of leaf flush, certain kinds of environmental stress may predispose perennial plants to outbreaks of early season folivores that restrict their feeding or oviposition to very young leaves.     

Allocation responses to CO2 enrichment and defoliation by a native annual plant Heterotheca subaxillaris

Among plants grown under enriched atmospheric CO₂, root:shoot balance (RSB) theory predicts a proportionately greater allocation of assimilate to roots than among ambient‐grown plants. Conversely, defoliation, which decreases the plant's capacity to assimilate carbon, is predicted to increase allocation to shoot. We tested these RSB predictions, and whether responses to CO₂ enrichment were modified by defoliation, using Heterotheca subaxillaris, an annual plant native to south‐eastern USA. Plants were grown under near‐ambient (400 μmol mol^?1) and enriched (700 μmol mol^?1) levels of atmospheric CO₂. Defoliation consisted of the weekly removal of 25% of each new fully expanded, but not previously defoliated, leaf from either rosette or bolted plants. In addition to dry mass measurements of leaves, stems, and roots, Kjeldahl N, protein, starch and soluble sugars were analysed in these plant components to test the hypothesis that changes in C:N uptake ratio drive shifts in root:shoot ratio. Young, rapidly growing CO₂‐enriched plants conformed to the predictions of RSB, with higher root:shoot ratio than ambient‐grown plants (P < 0.02), whereas older, slower growing plants did not show a CO₂ effect on root:shoot ratio. Defoliation resulted in smaller plants, among which both root and shoot biomass were reduced, irrespective of CO₂ treatment (P < 0.03). However, H. subaxillaris plants were able to compensate for leaf area removal through flexible shoot allocation to more leaves vs. stem (P < 0.01). Increased carbon availability through CO₂ enrichment did not enhance the response to defoliation, apparently because of complete growth compensation for defoliation, even under ambient conditions. CO₂‐enriched plants had higher rates of photosynthesis (P < 0.0001), but this did not translate into increased final biomass accumulation. On the other hand, earlier and more abundant yield of flower biomass was an important consequence of growth under CO₂ enrichment.     

Defoliation effects on carbon and nitrogen substrate import and tissue-bound efflux in leaf growth zones of grasses

Grassland plants suffer regular defoliation, causing loss of photosynthetic activity and internal resources. Consequently, re‐foliation may be substrate‐limited. The present study was undertaken to test the hypothesis that decreased C import in leaf growth zones is (partially) compensated by: (i) mobilization of substrate within growth zones; and (ii) increased efficiency of substrate use in leaf area expansion; but (iii) that these processes depend on the C status of growth zones at defoliation. Mixtures of a C₃ (Lolium perenne L.) and a C₄ grass (Paspalum dilatatum Poir.) were grown at 15 °C (C₃ dominance) and 23 °C (C₄ dominance). Individual plants thus grew in contrasting (light and temperature) environments before being defoliated. Defoliation caused a drastic and immediate decrease in C import, but effects on leaf area expansion were buffered by biomass mobilization in the growth zone and increases in specific leaf area of produced tissue. Thus, over the first 2 d post‐defoliation, the amount of leaf area produced per unit imported C increased by 39 to 102% depending on treatment. The magnitude of these buffering responses was correlated with the concentration of water soluble carbohydrates in the growth zone at defoliation. Similar responses were observed for N, although defoliation effects were smaller and delayed relative to those on C import. This study demonstrates refoliation is sustained by short‐term mobilization of reserves within the growth zone and reduced costs of produced leaf area, but that these mechanisms depend on growth zone C status at defoliation.     

Carbon integration in Plantago aristata (Plantaginaceae): the reproductive effects of defoliation

Patterns of carbon integration in aclonal species are poorly understood in spite of their potential to influence individual fitness. To provide more information about these patterns, we performed a defoliation experiment with P. aristata. We examined, at the metameric level, the reproductive responses to the removal of the major carbon sources within metamers. Bracts on marked reproductive spikes and leaves subtending these spikes were removed at three stages of reproductive maturity: spike elongation, flowering, and fruiting. Spike dry weight and length, capsule number, seeds per capsule, and seed weight were measured. We tested the hypothesis that seed weight would respond least to defoliation. We also performed a complementary ¹⁴C translocation experiment to measure the amount of radioactive carbon moving into the marked spikes from outside the metamer. Defoliation depressed all components of reproduction within marked spikes, and little ¹⁴C was translocated from outside the metamer into the reproductive spikes, even those that were defoliated. Both results support the view that reproductive metamers in this species are largely autonomous with respect to their carbon budget. Defoliation during spike elongation most depressed reproduction, and bract removal depressed reproduction more than did leaf removal. The data suggest that bracts compensate for leaf removal by increasing their photosynthetic rate; however, the ability to compensate differs among plant populations. Of all the reproductive components, seed weight was least affected by defoliation. The data show, however, that the time of defoliation relative to reproductive development influences which reproductive components are affected.     

Effects of Elevated CO2 and Defoliation on Compensatory Growth and Photosynthesis of Seedlings in a Tropical Tree,Copaifera aromatica1

After defoliation by herbivores, some plants exhibit enhanced rates of photosynthesis and growth that enable them to compensate for lost tissue, thus maintaining their fitness relative to competing, undefoliated plants. Our aim was to determine whether compensatory photosynthesis and growth would be altered by increasing concentrations of atmospheric CO₂. Defoliation of developing leaflets on seedlings of a tropical tree, Copaifera aromatica, caused increases in photosynthesis under ambient CO₂, but not under elevated CO₂. An enhancement in the development of buds in the leaf axils followed defoliation at ambient levels of CO₂. In contrast, under elevated CO₂, enhanced development of buds occurred in undefoliated plants with no further enhancement in bud development due to exposure to elevated CO₂. Growth of leaf area after defoliation was increased, particularly under elevated CO₂. Despite this increase, defoliated plants grown under elevated CO₂ were further from compensating for tissue lost during defoliation after 5¹/₂ weeks than those grown under ambient CO₂ concentrations.     

Grain Yield in Pearl Millet in Relation to Source Size and Proximity to Sink

Two pearl millet [Pennisetum glaucum (L.) R. Br. emend. Stuntz] hybrids GHB-30 and MH-179 were given defoliation treatments prior to anthesis comprising zero leaf to intact control. Keeping or removing even flag leaf only significantly altered the grain yield. With increasing leaf area (leaf numbers) the grain yield also significantly increased. Test mass showed more or less a similar trend. The leaves in the upper portion (nearer to sink) showed a greater contribution to the grain yield than the lower ones (away from sink). However, the highest leaf efficiency in terms of contribution per unit leaf area and the contribution by the whole leaf to the grain yield was recorded by 4^th and 3^rd leaf, respectively. The stem (covered with petioles) contributed to the extent of around 12 %. The existing leaves compensated to some extent for the defoliated ones.     

Effect of partial defoliation during the vegetative phase on subsequent growth and grain yield of maize

Maize was grown in two densities, 2–47 or 4–94 plants m^-2, and the following treatments imposed: untreated, plants partly defoliated 51 days after sowing, and alternate plants in a row partly defoliated 44 days after sowing. Plants flowered about 82 days after sowing. Leaf area was decreased by 60–64% by defoliation on day 51. Defoliation resulted in decreases in grain yield and grain number of 6–17%, though when alternate plants were defoliated in the higher density there was a substantial decrease in yield and number of grains in defoliated plants, which was largely offset by an increase in adjacent intact plants. When plants were defoliated on day 51 subsequent growth in leaf area was similar to, and that in leaf weight nearly as large as that in untreated plants, while increase in stem weight was substantially less than in untreated plants. By the time of flowering untreated and defoliated plots differed by c. 30% in leaf area. Increments of dry matter after flowering differed by c. 15% between untreated and defoliated plots. The fraction of these increments which entered the grain was c. 90% in both untreated and defoliated plots. When alternate plants in the row were partly defoliated on day 44 their subsequent increase in leaf area was probably 5–16% less than that of the adjacent intact plants. Increments of dry matter after flowering of plots with alternate plants defoliated were 93–95 % of those of untreated plots; leaf efficiency after flowering was slightly greater than in untreated plots. The fraction of the dry matter increment after flowering which entered the grain was c. 88 % in both intact and defoliated plants of the small density, but was 94% in intact plants and 86% in defoliated plants of the large density.     

Control and yield loss modelling of circular leaf spot of persimmon caused by Mycosphaerella nawae

Symptoms of circular leaf spot of persimmon (CLSP), caused by Mycosphaerella nawae, consisted of necrotic spots on leaves, chlorosis and premature defoliation. Although CLSP is a foliar disease, early fruit maturation and abscission are frequently associated with the presence of lesions on leaves and defoliation, resulting in severe economic losses. Despite their importance for the design of efficient disease management programmes, quantitative relationships between CLSP incidence and yield loss are unknown. Therefore, fungicide efficacy trials were conducted during two consecutive years in Spain to induce different levels of disease severity, defoliation and yield loss. The effects of fungicide treatments on CLSP severity were analysed by ordinal logistic regression models. Relative yield loss values were regressed against the percentage of affected leaves or defoliated obtained at different evaluation dates. The disease had high negative impact and complete yield loss was observed in the absence of effective fungicide treatments. Preventive applications of pyraclostrobin, trifloxy‐strobin and mancozeb provided the best disease control and highest yields, up to 95.77 kg tree^?1. An exponential relationship of CLSP incidence and defoliation with yield loss was found. In general, model fit and predictive ability was superior when defoliation, rather than incidence, was used as explanatory variable. The impact of defoliation on yield loss was higher in earliest evaluation dates, suggesting that early leaf abscission may be the main factor contributing to premature fruit drop and subsequent yield loss. Substantial yield losses were observed even with relatively low levels of CLSP incidence and defoliation. Therefore, it was not possible to define a critical action threshold for CLSP management based on foliar symptoms.     

Partial compensation in Psychotria marginata (Rubiaceae) after simulated defoliation increases photon capture and photosynthesis

We used Y-plant, a computer-based model of plant crown architecture analysis, to simulate effects of defoliation on daily canopy carbon gain in Psychotria marginata (Rubiaceae) plants under two contrasting irradiances. Five levels of defoliation were simulated using two different types of leaf blade damage. Compensatory increases in photon-saturated photosynthetic capacity (P _max) of 25, 50, and 100 % defoliation were also simulated. In all simulations daily photon capture and CO₂ assimilation increased with defoliation. However, without a compensatory response, daily canopy carbon gain also decreased with defoliation. Under high irradiance, reduction in daily canopy carbon gain was less than what would be expected if the response was proportional to leaf area reduction. Thus, 25 and 50 % defoliation resulted in only 20 and 41 % of daily canopy carbon gain reduction, respectively. In the scenario where 25 % of the leaf area was removed, if the P _max value was increased by 25 %, the remaining leaves compensated for 94 % of the daily canopy carbon relative to an undamaged non-compensated plant. At the same defoliation level, incrementing P _max values by 50 and 100 % resulted in overcompensation. Hence, because the increment of daily photon capture and CO₂ assimilation after defoliation was more a passive consequence of the reduction in leaf area than an active response, under the conditions tested photosynthetic compensation could be only possible through an active mechanism such as the increment of P _max values.     

Modelling the relationship between purple blotch and yield loss in garlic and effect of leaf damage on bulb yield

An AUDPC model was developed to describe the relationship between Alternaria porri infection and yield loss in garlic. Percentage yield loss was regressed against AUDPC and gave an acceptable fit to a linear model with an intercept of -0.35, a slope of 0.09 and R²= 0.85 during 1990–91 and an intercept of 1.91, a slope of 0.08 and R²= 0.87 during 1991–92. The effect of various levels of leaf damage on garlic bulb yield was also studied to simulate damage caused by A. porri. Significant yield reduction by 25% defoliation at 5 wk, 50% defoliation at 4 wk and 75% defoliation at 3 wk before bulb maturity were recorded. No significant yield reduction from 2 wk before bulb maturity could, however, be noticed even at the highest levels of leaf damage. Linear regression models were fitted for predicting yield at various levels of defoliation at different weeks before bulb maturity. These models can be used to describe the consequences of disease epidemics, projecting possible losses during the season and justifying the need for chemical disease control.     

Allocation to reproduction following experimental defoliation in Platanthera bifolia (Orchidaceae)

The roles of herbivory and pollination success in plant reproduction have frequently been examined, but interactions between these two factors have gained much less attention. In three field experiments, we examined whether artificial defoliation affects allocation to attractiveness to pollinators, pollen production, female reproductive success and subsequent growth in Platanthera bifolia L. (Rich.). We also recorded the effects of inflorescence size on these variables. We studied the effects of defoliation on reproductive success of individual flowers in three sections of inflorescence. Defoliation and inflorescence size did not have any negative effects on the proportion of opened flowers, spur length, nectar production or the weight of pollinia. However, we found that hand-pollination increased relative seed production and defoliation decreased seed set in most cases. Interactions between hand-pollination and defoliation were non-significant indicating that defoliation did not affect female reproductive success indirectly via decreased pollinator attraction. Plants with a large inflorescence produced relatively more seeds than plants with a small inflorescence only after hand-pollination. The negative effect of defoliation on relative capsule production was most clearly seen in the upper sections of the inflorescence. In addition to within season effects of leaf removal, defoliated P. bifolia plants may also have decreased lifetime fitness as a result of lower seed set within a season and because of a lower number of reproductive events due to decreased plant size (leaf area) following defoliation. Our study thus shows that defoliation by herbivores may crucially affect reproductive success of P. bifolia.     

Screening a cucumber crop during leaf area development reduces yield

In order to reduce heat energy consumption in greenhouse cucumber production, (transparent) screens may be used also during the day, particularly in the early growth phase when high temperatures are required to achieve rapid leaf area development. However, energy savings must be optimised against light reduction‐induced yield loss. For this reason, two experiments were conducted to quantify the effect on photosynthesis and growth of screening cucumber plants during their early growth phase, and on yield in the following generative phase. Screening with different light transmission coefficients was simulated using shading nets. Shading the plants during the first 5 weeks under Central European winter conditions reduced the leaf area by 0.40% per 1% reduction in photosynthetic active radiation (PAR). Moreover, potential leaf net photosynthesis decreased by 0.46% per 1% PAR reduction. A major impact was that the leaf dry matter content, leaf starch content and leaf sugar content of shaded plants diminished significantly. In the course of the following 2 weeks under full light, the leaf photosynthesis of the plants previously shaded recovered fully and the leaf area index rose to 3.3 m² m^?2, considered sufficient for optimal crop photosynthesis. The yield from plants previously shaded diminished slightly as early as from the first harvest week on. These yield losses increased further over the next few weeks, measuring approximately 0.8 kg m^?2 per 1 mol m^?2 day^?1 PAR reduction in the early growth phase. The effect of PAR on plant growth was proportional when relating the PAR integral over the entire experimental period to the total yield and to the total dry matter production, respectively.     

祁连山中部优势灌木物种叶功能性状参数变化特征

植物叶功能性状是连接植物与外界环境的重要桥梁,是探索植物适应环境、进行全球气候变化研究的指标,也是生态水文模型重要的输入参数。通过高时间分辨率样品的采集结合图像处理技术,对祁连山中部优势物种金露梅(Dasiphora fruticosa)和鬼箭锦鸡儿(Caragana jubata)叶功能性状变化特征进行研究,结果表明：叶面积(LA)从生长初期到生长末期发生明显变化,且2020年6—7月初灌木叶面积变化最为明显;比叶面积(SLA)分别在76—157 cm²/g之间和120—217 cm²/g之间,金露梅SLA平均值(123 cm²/g)<鬼箭锦锦鸡儿SLA平均值(176 cm²/g);在生长初期金露梅的叶面积指数(LAI)明显大于鬼箭锦鸡儿,金露梅和鬼箭锦鸡儿的叶面积指数随时间的变化都符合三次函数;生物量与基径和高度的乘积呈显著性相关,最优回归模型均为幂函数;地上生物量与叶功能性状参数在不同阶段的模拟方程均不同,地上总生物量与叶生物量在生长期的最优选择模型分别呈S型函数和幂函数,金露梅的单株地...     

Regrowth of spring canola (Brassica napus) after defoliation

Aims

Regrowth of dual-purpose canola after grazing is important for commercial success and the aim of this research was to investigate the effects of defoliation on the development, growth, photosynthesis and allocation of carbohydrates.

Methods

We conducted two pot experiments in which defoliation was conducted at multiple intensities with scissors. Experiment 1 determined changes in flowering date due to defoliation while Experiment 2 investigated the effects of defoliation on growth, photosynthesis and allocation of carbohydrates in canola.

Results

Time to the appearance of the first flower was delayed by up to 9 days after the removal of all leaves at the start of stem elongation (GS30), and up to 19 days if the elongating bud was also removed. Stem growth rate decreased by 56–86 % due to defoliation and tap roots did not increase in mass when plants were completely defoliated. Leaf area continued to expand at the same rate as in un-defoliated plants. The new leaf area established per gram of regrowth biomass over 20 days was 158 cm².g^-1 for the complete defoliation treatments compared with 27 cm².g^?1 for the half-defoliated treatment and 13 cm².g^?1 for the un-defoliated treatment. Despite a reduction in total biomass of up to 60 %, the proportion of dry matter partitioned to the leaves was 18 % for all treatments within 20 days after defoliation. Total non-structural carbohydrate levels were reduced rapidly in the stem by day two (predominately sucrose) and the tap root by day four (predominately starch) after defoliation and did not recover to match un-defoliated plant levels within 20 days. Residual leaves on defoliated plants maintained photosynthetic rate compared with the same leaf cohorts on un-defoliated plants in which photosynthetic rate decreased to 39 % by day 12.

Conclusions

The rapid recovery of leaf area in defoliated canola was facilitated by the sustained high photosynthetic rate in remaining leaves, rapid mobilisation of stored sugars (stem) and starch (root), and a cessation of root and stem growth.     

模拟及实地条纹黄瓜甲虫脱叶作用对‘Carolina’黄瓜光合反应的影响(英文)

１９９５年作者进行了田间试验来比较模拟的条纹黄瓜甲虫 Ａｃａｌｙｍｍａ　Ｖｉｔｔａｔｕｍ（Ｆ）脱叶作用及实地Ａ．ｖｉｔｔａｔｕｍ脱叶作用对‘Ｃａｒｏｌｉｎａ’黄瓜光合反应的影响。在５个生长阶段（从第一片真叶到收获）中,共模拟了６种脱叶水平（０％一１００％）。在每一生长阶段,每点植株每周两次用剪子去叶,这一处理叫连续脱叶。除此之外,对同一生长阶段植株也用了一次性脱叶处理,但只有４种脱叶水平（０,２５,５０及１００％）。用Ａ．ｖｉｔｔａｔｕｍ成虫笼养试验来估计实地害虫脱叶危害。每笼中甲虫放置时间为两周,密度各为每株０,１,３,５及１０头,测定其净光合速率。在模拟及实地害虫脱叶处理之间,没有测到显著的光合速率差异（ Ｐ＞０． ０５）。在模拟害虫脱叶试验中,受损叶片和未受损叶片的光合速率也很少有显著差异。结果显示模拟害虫脱叶处理过程不仅能准确反映实地Ａ．ｖｉｔｔａｔｕｍ脱叶危害下的‘Ｃａｒｏｌｉｎａ’黄瓜的生长反应,而且也适用于确定Ａ．ｖｉｔｔａｔｕｍ对黄瓜的经济危害水平。