Compensation in seasonal leaf area dynamics and leaf longevity after defoliation in Buddleja davidii

Buddleja davidii is a major invasive weed and its success is attributed to its ability to recover rapidly following defoliation. To quantify the impacts of defoliation on seasonal leaf area dynamics, we measured rates of leaf area growth and loss on cohorts of leaves on control plants and on plants that were defoliated by 66% repeatedly at monthly intervals throughout two growing seasons. The rate of leaf area growth was closely related to cumulative air temperature, but the maximum rate for the defoliated plants in the first season was 2.2 times that of the control plants. This compensational leaf growth resulted in 52% greater total emergent leaf area, attributable to increased node production (34%) and leaf size (35%), compared with control plants. Leaf longevity during the first growing season in the defoliated plants was 12% greater than that in the control plants. During the second season, the degree of compensation was greatly reduced, attributable to reduced leaf size in defoliated plants compared with the control. Total emergent leaf area over both seasons in the defoliated treatment exceeded control values by only 15%. The impact of leaf loss on the vigour in this invasive shrub may, in the short term, be less significant than would be predicted. However, the impacts of continued defoliation are likely to increase markedly in subsequent years. The study provides the basis for modelling leaf area dynamics and plant growth in response to defoliation associated with biocontrol release programmes.     

Fruit Quality and Yield in Partially Defoliated Strawberry Plants in the Tropical Highlands

The partial loss or reduction of leaf area is a wide-spread occurrence in the plant life cycle, caused e.g. by herbivory, stress or pathogen attack. The objective of the study was to evaluate the effect of partial defoliation on fruit production and quality in strawberry (Fragaria ×ananassa Duch. cv. Chandler). Plants were grown in a greenhouse in Tunja, Colombia, in hydroponics with an aerated nutrient solution. As leaves emerged, one or two leaflets were removed from each compound leaf, to attain 38 % and 67 % reduction of leaf area. Control plants grew intact, without defoliation. Fruit yield and fruit quality characteristics were evaluated for each plant. The pH, total soluble solids, ratio of total soluble solids to fruit juice acidity, fruit yield, fruit mass and size, and the ratio of leaf area/fruit yield were reduced drastically in defoliated plants. Leaf area reduction in excess of 38 % adversely affected physical and chemical characteristics of strawberry fruit, which did not meet marketing criteria.     

Tolerance of Faba Bean Plants (<Emphasis Type="Italic">Vicia faba</Emphasis>) to Partial Defoliation

Throughout the development of plants, certain biotic and abiotic phenomena can occur which reduce not only the photosynthetic area, but also the growth, depending on the stage of plant development. Responses by plants to defoliation depend on species, the timing of agricultural practices and the intensity level of defoliation. An experiment was carried out in Tunja, Colombia under greenhouse conditions, in order to evaluate the tolerance of faba bean plants (Vicia faba) to partial defoliation. Every week material was removed along each newly emerged leaflet to simulate 50% defoliation. Another group was grown with the entire leaf area to function as a control. As a result of partial defoliation, the specific leaf area, absolute growth rate, relative growth rate and total biomass were reduced, but the leaf weight ratio was increased. In addition, the pattern of dry matter partitioning was altered so that the amount of biomass accumulated was reduced in the roots, but increased in the leaves. Additionally, the partially defoliated plants showed the ability to partly restore the removed leaf area. In this way it could be inferred that the plants of Vicia faba present a moderate capacity to tolerate early defoliation during the vegetative phase.     

Tolerance of Spinach (Spinacia oleracea) Plants to Partial Defoliation

Vegetables in the tropics are grown continuously throughout the year due to the favorable climate. Unfortunately, leafy vegetables are often damaged because of slugs and snails. These mollusks and other herbivores cause different levels of defoliation to plants which can significantly impact their growth, production, and quality of the harvested product. A study was carried out in order to artificially simulate the effect of a loss in foliar area caused by these pests. The impact of severe artificial defoliation in spinach plants (Spinacia oleracea) was evaluated in Tunja, Colombia. Under greenhouse conditions and after transplanting, the plants had 75% of their leaf area removed. This procedure was repeated weekly on newly emerging leaves while a control group of plants was left intact. 71 days after transplanting, the plants were harvested, and the leaf area and dry weight of the plants were measured with which some allometric variables were calculated to express growth. Variables such as the number of leaves, plant height, total dry weight, relative growth ratio, leaf weight ratio (LWR), and root to shoot ratio (R:S) were unaffected by defoliation while leaf area, leaf area ratio (LAR), and specific leaf area (SLA) were reduced with the partial removal of the leaf area. The partial defoliation resulted in an increased partial biomass of the leaves. These results suggest that spinach plants have a moderate tolerance to partial defoliation.

     

Infection of sesame seed by Alternaria sesami (Kawamura) Mohanty and Behera and severity of Alternaria leaf spot in Kenya

Infection levels of Alternaria sesami in sesame (Sesamum indicum L.) seeds collected from farmers in western districts of Kenya were detected using the oatmeal agar plate method. Infection levels varied from 9% in Kakamega to 24% in Siaya. Samples from Busia had a mean infection level of 11.69%. Alternaria leaf spot was monitored in plots planted with Alternaria sesami infected seed at six different infection levels at Kibwezi to determine the effect of transmission of the fungus by seed on disease severity. Increase in per cent leaf area blighted and per cent defoliation fit more closely the Gompertz model than the logistic model. Rates of disease increase in blighted leaf areas and defoliation, and areas under disease progress curves (AUDPC), varied among the six seed infection levels. Infection levels with larger AUDPC generally had faster rates of disease progress. Disease was most severe on plants established from seeds with 8% infection and least on plants established from seeds with 0% infection. Disease severity increased with increased seed infection level.     

Weekly defoliation controls,but does not kill broad-leaved dock (Rumex obtusifolius)

Broad-leaved dock (Rumex obtusifolius L.) is a troublesome weed that predominantly grows in pastures and grassland. We hypothesised that frequent defoliation of Rumex will, over time, result in a reduction in root weight and leaf area, to the point where the impact on grass production is negligible. In order to investigate this hypothesis, we conducted three experiments. The objective of the first experiment was to perform a preliminary test of the hypothesis, using potted plants growing in the controlled conditions of a glasshouse. This experiment showed a rapid decline in leaf growth in plants that were defoliated weekly. The objective of the second experiment was to test the hypothesis in realistic outdoor conditions while still being able to collect detailed plant growth information. This experiment confirmed the findings of the glasshouse experiment and provided evidence that leaf growth ceased as a result of a dwindling supply of carbohydrate reserves in the root. Defoliated plants did not exhibit increased mortality. Finally, the objective of the third experiment was to test the hypothesis in a commercial pasture where normal field operations, specifically grass harvesting (three times) and slurry injection (twice), were performed. The results of this experiment were consistent with the results of the other two experiments. We conclude that weekly defoliation, maintained for three or more months, is an effective method to control (reduce the impact on grass production), but not kill, R. obtusifolius in pasture.     

Factors influencing infection of eucalypts by Cylindrocladium pteridis

The pattern of Cylindrocladium pteridis adhesion, germination and penetration in eucalypt leaves was assessed using scanning electron microscopy. The effects of inoculum concentration, leaf wetness period, plant age and branch position of cylindrocladium leaf blight and defoliation severity were assessed in greenhouse studies using two Eucalyptus grandis × E. urophylla hybrid clones. Penetration occurred through stomata, and there was no difference in the number of penetrations between young and old leaves. Percentage leaf area with lesions and defoliation increased with the increase in inoculum concentration (1 × 10² to 10⁵ conidia mL⁻¹), duration of leaf wetness period (6 to 48 h) and plant age (60 to 180 days). Branch position in plants also significantly affected the percentage leaf area with lesions and defoliation, the latter variable being significantly higher at the stem base. The highest values of lesion area were also observed on leaves at the stem base in both clones. The Pearson correlation between defoliation and leaf area with lesions was significant in all experiments ( r  > 0·9) indicating a high association between these two variables.     

Production,size, and germination of broad‐leaved dock seeds collected from mother plants grown under different nitrogen,phosphorus, and potassium supplies

Rumex obtusifolius is believed to be a nitrophilous weedy species that spreads mainly by seed. However, the effects of nutrient availability on seed production never have been investigated. In this study, how the amount of seed production per plant, the chemical composition of the seeds, and their size and germination are affected by the supply of N, P, and K was investigated. A pot fertilizer experiment with 10 treatments (combinations of 0, 150 [N1], and 300 [N2] kg N ha^?1, 0, 40 [P1], and 80 [P2] kg P ha^?1, and 0 and 100 [K] kg K ha^?1 applied twice per vegetation season) was carried out in Prague, Czech Republic, in 2008 and 2009. The seeds from plants that were cultivated since the spring were collected each August. The germination of the seeds was determined in long‐daylight conditions at a stable temperature of 20°C. The number of seeds per plant ranged from 0 in the P1 and P2 treatments and <200 in the control and K treatments to almost 9000 in the N2P2K treatment. The number of seeds per plant was positively correlated with the number of stems per plant and the number of seeds per stem. The relationship between the amount of seeds per plant and the individual seed weight was positive. The concentration of N, P, and K in the seeds was affected by the treatments. The weight of 1000 seeds ranged from 1.3 to 1.7 g. The seed length ranged from 2.11 to 2.34 mm and the seed width varied from 1.26 to 1.42 mm. With the exception of the control (with 94% germination), the amount of seed germination was >98% in all the other treatments in 2008. In 2009, the amount of seed germination was >95% in all the treatments, except N1 and N2, where 93% and 89% germination, respectively, was recorded. The germination rate was positively related to the P concentration in the seeds. The amount of time that was necessary for 50% seed germination ranged from 1.53 to 2.89 days and was not related to the N concentration in the seeds, but it was negatively related to the P and K concentrations. A balanced N, P, and K supply to the mother plant strongly affected the number of produced seeds and their chemical composition and germination ability.     

剑麻叶不同溶剂浸提液对假臭草萌发和生长的影响

以剑麻园常见伴生杂草假臭草为受体植物,白菜和萝卜为参照受体植物,采用生物测定的方法研究剑麻新鲜叶片石油醚、乙酸乙酯、三氯甲烷、蒸馏水4种溶剂浸提液对受体植物种子萌发和生长的影响。结果表明,4种溶剂浸提液对受体植物种子萌发率、根长和茎长生长均有不同程度的影响。500mg／mL蒸馏水浸提液和三氯甲烷浸提液对假臭草种子的萌发和幼苗的根长总体上具有显著的抑制作用,抑制率分别达到29％和50％;500mg／mL蒸馏水浸提液对萝卜种子萌发和根长生长具有显著的抑制作用,抑制率分别达到45．00％和64．22％;500mg／mL乙酸乙酯浸提液对白菜种子萌发和根长生长的抑制作用较强,抑制率分别达到30．49％和56．59％。说明剑麻不同溶剂、不同浓度浸提液对不同的受体植物均存在不同程度的化感作用,这为进一步开展利用剑麻的化感物质抑制杂草的研究提供了理论基础。     

杂草稻对水稻生长及产量的影响

通过室内试验和田间试验明确了杂草稻对水稻生长、产量构成因子和产量的影响。水稻营养生长期,不同杂草稻密度对水稻基本苗、株高、单株鲜重、分蘖、倒二叶长与宽均没有影响。而水稻株高、有效穗数、穗长、一次枝梗数、穗粒数、千粒重、结实率、实际产量等均随杂草稻密度的增加而呈现下降趋势。杂草稻密度为1株/m2可导致水稻产量损失9.15%,当杂草稻密度达7株/m2时可导致水稻产量损失50%以上,杂草稻密度达到12株/m2时水稻产量损失可高达72.29%。     

Environmental maternal effects on seed morphology and germination in Sinapis arvensis (Cruciferae)

Pioneer plants are adapted to grow in unpredictable environments. These plants have evolved several traits related to seed morphology and germination to cope with this unpredictability. The main aim of this study was to investigate the effect of plant identity and maternal environment on seed mass and germination of Sinapis arvensis. This study was undertaken with S. arvensis plants grown in four experimentally manipulated resource availability scenarios: (i) nitrogen addition, (ii) water addition, (iii) nitrogen and water simultaneously added, and (iv) control. Plants grew under field conditions in an emerging plant community. Germination response was mainly affected by maternal plant identity. This reflects not only genotype quality but also phenotypic plasticity, which allows adaptation to habitat conditions. Seed coat colour together with mean seed mass per plant explained significant fractions of the variability in germination rate. Changes in the germination response because of maternal environmental effects were also detected. Germination rate decreased in seeds from nitrogen‐enriched conditions; this may be due to the induction of dormancy caused by high concentration of nitrogen in the seeds. Addition of water to maternal environment caused a decrease in total germination percentage and germination rate of seeds. Thus, our results provide evidence for maternal environmental effects on germination under field conditions. Furthermore, changes in germination timing, as detected in our study, may determine plant development and fitness in unpredictable conditions.     

Yield loss of sweet corn cultivars in response to defoliation and to infection byexserohilum turcicum

The effect of northern leaf blight (NLB) or leaf defoliation on the yield of nine sweet corn cultivars was studied in field experiments. Plants were defoliated or infected in the bottom, middle or top third of the leaf canopy. The effect of defoliation or infection on yield was significantly higher for plants treated 55 days after planting than for those treated 70 days after planting. Cultivar response differed significantly for both treatments, the most sensitive cultivar being ‘Jubilee’ and the least sensitive being Ssupersweet 7900. In all cases, the highest yield loss was recorded when the middle third of the leaf canopy was treated. The relative importance of the top third of the leaf canopy increased if the treatment was done 3 weeks before harvesting. This study emphasized the importance of leaf position, cultivar, and plant growth stage for evaluating losses caused by NLB, and may explain the failure of various models to describe yield loss due to NLB.     

Inhibitory effects of aqueous extracts of black mustard on germination and growth of alfalfa

The present study investigated the allelopathic effects of various black mustard ( Brassica nigra L.) plant parts on alfalfa germination and seedling growth. Aqueous extracts of black mustard ( Brassica nigra L.) leaf, stem, flower and root plant parts were made to determine their effects on germination and dry weights of hypocotyl, and radicle length of 5-day-old alfalfa seedlings over a range of extract concentrations. All aqueous extracts significantly inhibited alfalfa seed germination and seedling growth when compared with the distilled water control. Increasing the aqueous extract concentrations of separated Brassica nigra plant parts significantly inhibited alfalfa germination, seedling length and weight. Based on significant radicle length reactions to aqueous extracts, the toxicity may be classified in the following order of decreasing inhibition: flower, leaf, mixture of all plant parts, root, and stem. Increasing the concentration of aqueous flower extracts significantly inhibited the water uptake by germinated alfalfa seeds. The greatest inhibition in water uptake occurred at a 12 g kg⁻¹ extract concentration for seeds soaked for 8 h.     

THE EFFECT OF INTRA-SPECIFIC COMPETITION ON THE DEVELOPMENT OF CHENOPODIUM ALBUM L.

Summary. Plants of Chenopodium album L. were grown at a range of different densities in each of three years. The stem diameter, the number of main branches and the size and number of leaves decreased with increasing density as did weight and leaf area per plant. The dry-matter yield per unit area increased with density up to 576 plants/m² in two of the three trial years. The proportion of the seed yield relative to the total yield was higher in the leas dense than in the dense stands, or was almost constant. Density did not affect the seed yield per unit area, but seed yield per plant fell as density increased. Maximum seed production was 41 900 per plant and the mean seed yield over the three years was 8300 seeds per plant. The percentages of nitrogen, phosphorus, potassium and calcium were highest when the plants were at an early stage of development. The proportions of these elements in the dry-matter yield decreased with increasing age of the plants. The density of the stand did not affect the percentages of elements but the total amounts per plot were greatest at the flowering stage and in the denser stands.     

THE INTERRELATIONSHIP BETWEEN TILLERS AND RHIZOMES OF POA PRATENSIS L.—AN AUTORADIOGRAPHIC STUDY

Summary. The main shoot or selected tillers of seedling plants of Poa pratensis L. were supplied with ¹⁴CO₂ and the distribution of ¹⁴C-assimilates was followed by autoradiography. The primary tillers were initially supplied with ¹⁴C-assimilates from the main shoot but, once established, became independent of the parental shoot for carbohydrates. Similarly, developing rhizome-tillers were supported by the main shoot and established primary tillers but soon became self-supporting, Defoliation of all the tillers of the plant but one led to the defoliated primary and rhizome tillers being supplied with radiocarbon from the remaining intact shoot. Thus, although the primary tillers and rhizome-tillers in the intact plant appear to be physiologically independent, the entire tiller-rhizome system may be re-integrated after defoliation, allowing assimilate redistribution. P. pratensis may be regarded as a convenient link between the non-weedy herbage grasses which generally lack rhizomes and the weedy rhizomatous grasses typified by Agropyron repens (L.) Beauv.
Etat des relations entre les talles et les rhizomes de Poa pratensis L. Etude autoradiographique     

沟灌渗透对直播水稻干物质积累和产量的影响

采用田间对比试验、植株分析方法,研究了相同畦宽(200cm)、不同灌水量的沟灌渗透栽培和常规淹水栽培对直播水稻茎蘖生长及干物质积累的影响。结果表明:不同时期直播水稻茎蘖生长、干物质积累、冠层叶性状和产量在不同处理之间均存在一定的差异;其中,以处理1(节水38.6%的沟灌渗透)的茎蘖生长适宜,分蘖质量高,干物质积累量大,冠层叶叶绿素含量高,有效穗数、穗长、穗粒数、实粒数和千粒重显著高于常规淹水处理,增产达8.74%。     

Influences of herbicides, uprooting and use as cut flowers on sexual reproduction of Solidago canadensis

Solidago canadensis is a noxious invasive species in China. We examined the influences of herbicides on pollen germination and pollen tube growth and the effects of cutting flowers and herbicides on seed production and quality. We also determined the seed production and resource allocation to different organs of S. canadensis after uprooting the plants during their reproductive periods. The main results were as follows: (i) 49% pollen of S. canadensis was able to germinate on an appropriate medium; (ii) compared with paraquat, ethephon and 2,4-D, glyphosate had an ideal inhibitory effect on pollen germination and the formation of seeds of S. canadensis ; (3) cut flowering branches, when placed in water or nutrient solution, were still able to produce viable seeds; (4) resources were allocated more to the inflorescences to facilitate seed maturation after plants were uprooted at the flowering stage. Uprooted flower branches were still able to produce viable seeds, especially those in full flower. Therefore, in order to reduce the seed production of S. canadensis and spread of the species we suggest: (i) apply glyphosate at the flower bud stage, (ii) completely destroy uprooted plants at flowering stages and (iii) avoid using the flowering branches as ornamental materials.     

分根灌溉对干旱区棉花生长干物质分配和产量的影响

本试验旨在观测分根灌溉(Partial Rootzone Irrigation,PRI)棉花能否在降低灌溉量的条件下维持一定的经济产量。田间实验的灌溉方式分为2种:交替隔沟灌溉(Alternative Furrow Irrigation,AFI)、固定隔沟灌溉(Fixed Furrow Irrigation,FFI)和常规灌溉(Conventional Furrow Irrigation,CFI)。结果表明,在降低30%灌溉量的条件下,棉花籽棉产量略有减少,AFI和FFI的籽棉总产量分别为CFI的92%和84%,但AFI比CFI的霜前花产量高出12%。PRI处理的棉花叶面积、株高及叶片、桃和茎的干物质量都低于CFI,但单株平均桃数与CFI没有显著差异。在降低灌溉量的条件下,由于霜前花价格比较高,AFI基本上能够维持棉花的经济产量不降低。     

Allelopathic effect of leaf debris, leaf aqueous extract and rhizosphere soil of Ophiopogon japonicus Ker-Gawler on the growth of plants

Laboratory and greenhouse experiments were conducted to evaluate the allelopathic potential of dwarf lily turf ( Ophiopogon japonicus Ker-Gawler) on lettuce, alfalfa, timothy and mustard plant growth. Dry leaf debris, aqueous extract of fresh leaves and O. japonicus grown soil were investigated. Emergence, dry weight, and root and shoot length of all bioassay species were inhibited when grown in soil incorporated with oven-dried leaves of O. japonicus. The inhibitory effects were often dependent on the concentration. However, the degree of inhibition varied among the test plant species. The aqueous leaf extract was highly phytotoxic and it significantly reduced germination, seedling growth, and the fresh weight of all the test species at all rates. The emergence and growth of all four tested plants were severely inhibited when planted in O. japonicus contaminated soil. These results indicate that O. japonicus incorporated leaf debris, leaf aqueous extract and its rhizosphere soil suppress seed germination, radicle growth, seedling emergence and seeding growth of certain weeds and suggest that these responses were attributed to an allelopathic effect.     

Barley yield losses due to defoliation of upper three leaves either healthy or infected at boot stage by <Emphasis Type="Italic">Pyrenophora teres</Emphasis> f. <Emphasis Type="Italic">teres</Emphasis>

This paper evaluates, in the greenhouse and under natural conditions, barley yield losses due to defoliation treatments of the upper three leaves either healthy or infected at the boot stage by Pyrenophora teres f. teres. Defoliation was assumed as a loss of a similar leaf area caused by net blotch disease severity of 100%. Contribution to grain yield was defined herein as a difference between defoliation treatments and a treatment where plants lost all their upper three leaves. In contrast, yield losses referred to differences in yield between defoliations and the control. In the greenhouse, removal of the antepenultimate leaf did not affect any yield component. For main stems, defoliating upper three leaves reduced grain yield by 30% and this was mainly due to flag leaf removal. These losses were similar to those induced by net blotch disease under natural conditions, but were of 42% for all tillers. Grain yield losses due to disease severity were not equivalent to the defoliation effect of a similar healthy leaf area. On the other hand and for a significant contribution to grain yield, flag leaf was dependent on the presence of the other two leaves. Inoculation and defoliation of 21 cultivars induced similar grain yield losses of 32%. However, biotic stress reduced by 40% the contribution of their upper three leaves. Under field conditions, yield losses were not significant until barley plants lost more than one upper leaf and flag leaf contribution was equivalent to that of the remaining leaves. Characteristic roots, defined as leaf coefficients for plant performance, were 0.13, 0.06 and 0.01 for the flag, penultimate and antepenultimate leaves, respectively. Because antepenultimate leaves become trivial at the boot stage, we propose that coefficients of the remaining leaves should be used when modelling yield losses due to barley foliar diseases.