Light interception efficiency explained by two simple variables: a test using a diversity of small- to medium-sized woody plants

? Plant light interception efficiency is a crucial determinant of carbon uptake by individual plants and by vegetation. Our aim was to identify whole-plant variables that summarize complex crown architecture, which can be used to predict light interception efficiency. ? We gathered the largest database of digitized plants to date (1831 plants of 124 species), and estimated a measure of light interception efficiency with a detailed three-dimensional model. Light interception efficiency was defined as the ratio of the hemispherically averaged displayed to total leaf area. A simple model was developed that uses only two variables, crown density (the ratio of leaf area to total crown surface area) and leaf dispersion (a measure of the degree of aggregation of leaves). ? The model explained 85% of variation in the observed light interception efficiency across the digitized plants. Both whole-plant variables varied across species, with differences in leaf dispersion related to leaf size. Within species, light interception efficiency decreased with total leaf number. This was a result of changes in leaf dispersion, while crown density remained constant. ? These results provide the basis for a more general understanding of the role of plant architecture in determining the efficiency of light harvesting.     

Effects of spacing interval of wide bed planting on canopy characteristics and yield in winter wheat

2010-2012连续两年在大田试验条件下以多穗型品种‘百农矮抗58’为供试材料, 研究了宽幅播种(播幅8 cm)种植方式下不同带间距7 cm (KF7)、12 cm (KF12)和17 cm (KF17)对冬小麦(Triticum aestivum)冠层特征及产量的影响。结果表明: 与常规条播比较, 宽幅播种群体叶面积指数、平均叶倾角、光截获量、相对湿度、成穗数、生物量和产量较高, 而冠层开度和温度较低; 2010-2011年和2011-2012年宽幅播种成穗数和产量显著高于常规条播, 成穗数分别增加4.8%-16.4%和8.9%-21.0%, 产量分别提高2.96%-15.94%和4.09%-14.23%。宽幅播种下随带间距增大, 叶面积指数、平均叶倾角、光截获量、湿度及成穗数降低, 而冠层开度和温度升高; 穗粒数、千粒重、产量、生物量和收获指数以KF12最高, KF7最低。综合分析, 宽幅播种下12 cm带间距处理的小麦冠层结构合理, 微环境适宜, 产量最高, 可作为该种植方式的适宜带间距。     

Increase in light interception cost and metabolic mass component of leaves are coupled for efficient resource use in the high altitude vegetation

Global syntheses of leaf trait scaling relationships report an increase in light interception costs or ‘diminishing returns’ with increase in leaf area. However, variation in light interception costs across ecological gradients and plant strategies to cope up with these costs are not adequately understood. We analyzed leaf area (A) – leaf dry mass (M), leaf water mass (W) – M and W – A scaling relationships in plants occurring in a high altitude region of western Himalaya across environmental gradients to understand changes in light interception cost and metabolic mass component. M represents light interception cost, whereas, W is considered as a proxy of metabolic mass component for liquid phase being the ultimate source of metabolic activity. Trait values were measured from 9278 leaves belonging to 136 dominant species occurring at different sites, slope aspects, elevations and habitat types. Overall, light interception cost increased with increasing A (scaling exponent (α) < 1 in A–M relationship) and metabolic mass component increased disproportionately high with increasing M and A. We found significant differences in scaling exponents of leaf trait relationship between sites, elevations, slope aspects and habitat types, indicating that increase in light interception cost was more evident at higher elevations, southern slopes and open habitats. Further, with increase in light interception cost, metabolic mass component also increased (α > 1 in W–M and W–A relationships). The changes in scaling exponents of various leaf trait relationships across ecological gradients indicated that vegetation of different regions have differences in light interception cost and metabolic mass component. Moreover, increasing light interception cost (increase in mechanical and hydraulic tissues) with increasing A and increasing metabolic mass (leaf thickness) with increasing A and M are favored in high altitude vegetation. This could be a key strategy of high altitude plants for efficient resource capture and use in harsh environments.     

辽东栎叶片昆虫取食形状多样性及其变化模式

取食辽东栎(Quercus liaotungensis)叶片的植食性昆虫有丰富的多样性和重要的生态功能,昆虫取食叶片留下的形状变化多,易观察,可以作为昆虫物种多样性监测的手段之一。研究北京西部东灵山地区辽东栎叶片被植食性昆虫取食状况,发现昆虫对辽东栎叶片的危害非常普遍,叶片被食频率约为90％,被食面积约5％,取食状可分为9类,其中以缘食和孔食为主,共记录20余种植性昆虫,其中蛾类幼虫和甲虫是主要取食种类,植食性昆虫集中出现在叶片发育的早期阶段（5－6月份）,7月份后,大多数幼虫发育成熟,取食叶片的面积减少。各取食状所涉及昆虫种类的组成不同,面积呈不同的季节变化模式,其中缘食状和孔食状之间有显著的正相关关系;辽东栎叶片在展叶初的叶面积最低,在7月底均达到最大值,然后呈下降趋势,单位面积重量也在展叶初最低,在6月底接近最大值,不同坡向的辽东栎林和叶片面积,单位面积重量及叶片被食面积均有显著差异,偏阳坡（东南坡） 高于偏阴坡（西北坡）。以上结果表明,辽东栎叶片维持了昆虫物种多样性,昆虫的生长发育与辽东栎的物候规律相互协调,昆虫种类的取食呈季节和空间变化。     

Evaluation of some fungal diseases and yield of groundnut in groundnut-based cropping systems

A study on the evaluation of some fungal diseases and yield of groundnut in groundnut-based cropping systems was conducted in 2002 and 2003 planting seasons. Analysis of variance indicated that intercropping was highly significant on leaf spot disease severity 0.76; 0.75, rust 2.75; 2.69, as well as percentage defoliation 78.42%; 78.10% in 2002 and 2003, respectively. Plant population was significant on leaf spot severity 4.52, 4.60 rust 2.76; 366 and defoliation 226.5; 441.1 fungal as well as yield, while interactions were not significant on the fungal diseases and yield. Sole groundnut recorded significantly high severity of the fungal diseases investigated but low yield, when groundnut was intercropped with maize and melon and recorded the lowest yield in 2002 and 2003 respectively. 250,000 plants/ha recorded the lowest severity of the diseases investigated, while 444,444 plants/ha recorded the highest. Sole groundnut also recorded the highest percentage defoliation 79.37%, 79.25% when groundnut was intercropped with maize recorded the lowest 77.06%; 77.60%. 250,000 plants/ha had the lowest defoliation when 444,444 plants/ha had the highest 80.75% 82.13% in 2002 and 2003, respectively. Sole groundnut recorded the lowest in the majority of yields when intercropped with maize and with melon recorded a high yield and yield components in 2002 and 2003, respectively. The microorganisms identified were Cercospora spp., Aspergillus linked and Blastomyces.     

Relationship between leaf area index and yield in double-crop and full-season soybean systems

Previous research indicates a correlation between leaf area index (LAI) and yield of full-season soybean [Glycine max (L.) Merrill], which is a single crop planted early in the season. Leaf area index values of at least 3.5-4.0 in the reproductive stages are required for maximum potential yield. It is unknown how yields of double-crop soybean, which is planted late into harvested small grain fields, respond to changes in leaf area index. We hypothesized that double-crop soybean would be more sensitive to defoliation than full-season soybean. This study used linear and linear plateau models to describe the yield response of full-season and double-crop soybean to reductions in leaf area index through manual defoliation, and evaluated the yield response of double-crop soybean to reductions in leaf area index through natural insect defoliation. From 15 manual defoliation experiments over 3 yr, significant linear decreases in yield occurred in both full-season and double-crop soybean when leaf area index values were below 3.5-4.0 by developmental stages R4 to R5, whereas yields usually reached a plateau at higher leaf area index levels. Average yield loss was 769 +/- 319 kg ha(-1) for each unit decrease in leaf area index below the plateau; average maximum yield was 3,484 +/- 735 kg ha(-1). From eight field experiments over 2 yr, insect defoliators had no effect on double-crop soybean yield; leaf area index levels were above 4.0 by the developmental stage when leaf area index estimates were taken (R3 to R6). Therefore, double-crop soybean that maintains leaf area index values above the 3.5-4.0 critical level by mid-reproductive developmental stages can tolerate defoliating pests.     

Resource allocation in an annual herb: Effects of light,mycorrhizal fungi,and defoliation

Concurrent interactions and the availability of resources (e.g., light) affect the cost/benefit balance during mutualistic and antagonistic interactions, as well as plant resource allocation patterns. Mycorrhizal interactions and herbivory concur in most plants, where mycorrhizae can enhance the uptake of soil nutrients by plants as well as consuming a large fraction of the plant's carbon, and defoliation usually reduces light interception and photosynthesis, thereby causing direct losses to the hosts of mycorrhizal fungi. Both types of interactions affect the carbon budget of their host plants and thus we predict that the relative costs of herbivory and mycorrhizal colonization will increase when photosynthesis is reduced, for instance in light limited environments. We conducted a greenhouse experiment using Datura stramonium to investigate the effects of defoliation and mycorrhizal inoculation on the resource allocation patterns in two different light environments. Defoliated plants overcompensated in terms of leaf mass in both light environments, but total seed mass per fruit was negatively affected by defoliation in both light environments. Mycorrhizal inoculation had a positive effect on vegetative growth and the leaf nitrogen content, but defoliation negates the benefit of mycorrhizal interactions in terms of the leaf nitrogen content. In general, D. stramonium compensated for the relative costs of concurrent mycorrhizal interactions and defoliation; plants that lacked both interactions exhibited the same performance as plants with both types of interactions.     

Photosynthetic responses of wheat, Triticum aestivum L., to defoliation patterns on individual leaves

The impact of defoliation by fall armyworm, Spodoptera frugiperda (J. E. Smith), on the photosynthetic rates of injured, individual wheat, Triticum aestivum L., leaves and the impact of different spatial patterns of artificial insect defoliation on photosynthesis of remaining leaf tissue of injured, individual wheat leaves were evaluated in this study. Photosynthesis, stomatal conductance, transpiration, and chlorophyll a fluorescence were recorded in the flag-leaves of wheat plants 1 and 24 h after defoliation in 2003 and at 1 h, 24 h, 7 d, and 14 d after defoliation in 2004. Photosynthesis of injured leaves was not significantly affected by any defoliation treatment (i.e., control, natural, and artificial). Similarly, we did not observe interactions between defoliation treatments and time after defoliation. Stomatal conductance was significantly affected by time after defoliation and by the interaction between defoliation treatment and time after defoliation. However, in general, our results showed that wheat responded similarly to insect defoliation and artificial defoliation, which, therefore, may be used to simulate leaf mass consumption. Spatial defoliation patterns had a significant effect on photosynthetic parameters of injured leaves, but responses were dependent on plant developmental stages. The chlorophyll a fluorescence data revealed no significant effects from any defoliation pattern on the photochemical efficiency of the injured leaf. No significant interactions between defoliation patterns and time after defoliation were observed. Our findings reveal that the spatial pattern of defoliation in wheat affects photosynthetic and other gas exchange responses, which suggests that when simulating insect defoliation in wheat, researchers need to be cognizant of the defoliation pattern to adequately simulate insect defoliation.     

Simple equations to estimate light interception by isolated trees from canopy structure features: assessment with three-dimensional digitized apple trees

* Simple models of light interception are useful to identify the key structural parameters involved in light capture. We developed such models for isolated trees and tested them with virtual experiments. Light interception was decomposed into the projection of the crown envelope and the crown porosity. The latter was related to tree structure parameters. * Virtual experiments were conducted with three-dimensional (3-D) digitized apple trees grown in Lebanon and Switzerland, with different cultivars and training. The digitized trees allowed actual values of canopy structure (total leaf area, crown volume, foliage inclination angle, variance of leaf area density) and light interception properties (projected leaf area, silhouette to total area ratio, porosity, dispersion parameters) to be computed, and relationships between structure and interception variables to be derived. * The projected envelope area was related to crown volume with a power function of exponent 2/3. Crown porosity was a negative exponential function of mean optical density, that is, the ratio between total leaf area and the projected envelope area. The leaf dispersion parameter was a negative linear function of the relative variance of leaf area density in the crown volume. * The resulting models were expressed as two single equations. After calibration, model outputs were very close to values computed from the 3-D digitized databases.     

Field resistance of two soybean germplasm lines, HC95-15MB and HC95-24MB, against bean leaf beetle (Coleoptera: Chrysomelidae), western corn rootworm (Coleoptera: Chrysomelidae), and Japanese beetles (Coleoptera: Scarabaidae).

Two recently released, Mexican bean beetle, Epilachna varivestis, Mulsant, resistant soybean, Glycine max (L.) Merrill, germplasm lines, HC95-15MB and HC95-24MB, were examined for foliar and pod feeding resistance to adult bean leaf beetles, Cerotoma trifurcata (Forster), western corn rootworms, Diabrotica virgifera virgifera LeConte, and Japanese beetles, Popillia japonica Newman. Both lines were planted along with a susceptible control cultivar in 18 by 30-m plots and separate 0.8-ha size fields. Insects were sampled on a weekly basis with a sweep net. In late summer, defoliation ratings were recorded along with data on percentage pod feeding. Although a few significant differences in insect densities were obtained among the soybean lines on some sampling dates, no specific trends were observed in the ability of the resistant germplasm to reduce insect numbers. Insect population densities were similarly on all lines. However, both resistant lines were able to reduce defoliation during the growing season. Conversely, percentage pod feeding was similar among all the soybean lines, with no differences observed. The resistant germplasm lines appear able to lower levels of defoliation, and thus, offer a potential management tactic where leaf feeding, i.e., defoliation, is of concern. However, their ability to greatly reduce beetle population densities, and for the bean leaf beetle, to reduce pod feeding, appears limited.     

Defoliation increases carbon limitation in ectomycorrhizal symbiosis of <Emphasis Type="Italic">Betula pubescens</Emphasis>

Boreal forest trees are highly dependent on root-colonizing mycorrhizal fungi. Since the maintenance of mycorrhizal symbiosis implies a significant carbon cost for the host plant, the loss of photosynthetic leaf area due to herbivory is expected to reduce the host investment in mycorrhizae. We tested this hypothesis in a common garden experiment by exposing ectomycorrhizal white birch (Betula pubescens Ehrh.) seedlings to simulated insect defoliation of 50 or 100% intensity during either the previous or the current summer or repeatedly during both seasons before harvest. The shoot and root growth of the seedlings were distinctly reduced by both 100% defoliation and repeated 50% defoliation, and they were more strongly affected by previous-year than current-year defoliation. The root to shoot ratio significantly decreased after 100% defoliation, indicating reduced proportional allocation to the roots. Ergosterol concentration (i.e. fungal biomass) in the fine roots decreased by 100% defoliation conducted either in the year of harvest or in both years. No such decrease occurred following the 100% defoliation conducted in the previous year, indicating the importance of current photosynthates for fungal symbionts. The trend was similar in the colonization percentage of thick-mantled mycorrhizae in the roots, the most marked decline occurring in the repeatedly defoliated seedlings. The present results thus support the prediction that the plant investment in ectomycorrhizae may decline as a response to foliage loss. Moreover, the colonization percentage of thick-mantled mycorrhizae correlated positively with the ratio of leaf to heterotrophic plant biomass in the defoliated birch seedlings, but not in the control ones. This tends to indicate a stronger carbon limitation of ectomycorrhizal colonization in defoliated seedlings.     

Determinants of mountain birch growth in situ: effects of temperature and herbivory

Variation in in situ growth performance of the mountain birch as indicated by the widths of annual rings was analysed and related mainly to temperature and herbivory using ring width series from five heath forest sites in the Lake Torneträsk area, northern Sweden. Climate explained 48–64% of the variation in age-corrected mean ring width series. In general, the effect of current year July followed by June temperature was most important at all sites. A warm May resulted in wider rings due to an earlier budburst. Short-term (inter-annual) responses to increased temperature were in most cases not reflected into long-term responses (decades). A large proportion of the variation in stem mean ring width was due to variation among stems within trees (81%) in these polycormic trees, while variation among sites was marginal (0.4%). Within trees, main stems grew faster and were more responsive to climate variation than subordinate stems. No effect of insect herbivory on ring width was found at low defoliation levels (≤12%). At a defoliation level of ca 84% a one-year reduction in stem growth was observed while the growth reduction (ca 50% reduction in ring width) lasted for 4 yr after ca 93% defoliation. After outbreaks resulting in complete defoliation and some stem mortality, ring widths of surviving stems mainly responded with increased growth. Basal sprouts, emerging just after a severe insect outbreak with a high mortality of old stems, grew faster than sprouts occurring during other periods. It is concluded that the mountain birch is well adapted to recover from Epirrita outbreaks; the ability to produce basal sprouts, that can benefit from an existing root system for fast initial growth, is one important mechanism for this.     

Light regime in relation to plant population geometry

Plant population geometry effective in light utilization for photosynthesis was examined with the use of square-planted (SP) population models and the Monte Carlo technique. Varying SP populations were constructed by manipulating the structural variables, leaf area density, leaf size, leaf number, height/width ratio of unit stand and planting distance, of the unit stand with standard configurations treated in the second paper. Leaf area index was fixed to be 5, and the phyllotaxis, 1/3. The effects of these structural variables on the light extinction in the SP populations were made clear with light-beam emission experiments in a computer. Special combinations of the variables could make light extinction in the infinite population approximately linear with increasing leaf area index to obtain the highest photosynthesis of the foliage, i.e., each leaf layer from top to bottom of the population could uniformly utilize light energy for photosynthetic production.     

浙江天童常绿阔叶林石栎叶片昆虫取食状类型和取食强度研究

在浙江天童常绿阔叶林中随机选择10株石栎（Lithocarpus glaber）大树,每株选择冠层向阳枝条2枝,取其所有成熟叶片（2332片）对昆虫取食状类型和取食强度进行了分析。结果表明,石栎叶片昆虫取食状类型多样,计有15种,但出现频度有很大不同;顶食状和缘食状的频度分别在30％以上;切叶状、连续小孔状和大孔状的频度在10％～30％：小孔状、阴面食状、叶中脉、泡状的频度在6．4％～1．5％;其余6种类型的频度〈1％。对叶片的危害程度取决于取食面积和频度,顶食状等3种类型频度高、取食面积大,对叶片的危害重;而阴面食状等11种类型取食面积较小,频度低,对叶片的危害较小;连续小孔状尽管取食频度高,但取食面积小,对叶片的危害也小。连续小孔状和切叶状之间存在显著正相关,但连续小孔食状与阴面食状之间,切叶状、连续小孔食状与小孔食状之间则存显著负相关,其它取食状之间均没有显著相关性,反映出不同昆虫类型的取食生态位关系。石栎叶片昆虫取食率为13．6％,介于温带森林和热带森林之间;但石栎叶片的昆虫取食频率64％,小于辽东栎,可能是由于防御机制上的差异所至;此外,石栎叶片昆虫取食强度还受到植株本身因素和小生境等因素的影响。     

Mineral nutrition and growth of tropical maize as affected by soil acidity

Soil constraints linked to low pH reduce grain yield in about 10% of the maize growing area in tropical developing countries. The aim of this research was to elucidate the reasons for this maize yield reduction on an oxisol of Guadeloupe. The field experiment had two treatments: the native non-limed soil (NLI, pH 4.5, 2.1 cmol Al kg^–1, corresponding to 20% Al saturation), and the same soil limed 6 years prior to the experiment (LI, pH 5.3, 0 cmol Al kg^–1). The soils were fertilized with P and N. The above-ground biomass, root biomass at flowering, grain yield and yield components, leaf area index (LAI), light interception, radiation-use-efficiency (RUE), P and N uptake, soil water storage, and soil mineral N were measured during the maize cycle. The allometric relationships between shoot N concentration, LAI and above-ground biomass in LI were similar to those reported for maize cropped in temperate regions, indicating that these relationships are also useful to describe maize growth on tropical soils without Al toxicity. In NLI, soil acidity severely affected leaf appearance, leaf size and consequently the LAI, which was reduced by 60% at flowering, although the RUE was not affected. Therefore, the reduction in the above-ground biomass (30% at flowering) and grain yield (47%) were due to the lower LAI and light interception. At flowering, the root/shoot ratio was 0.25 in NLI and 0.17 in LI, and the root biomass in NLI was reduced by 64% compared to LI. Nitrogen uptake was also reduced in NLI in spite of high soil N availability. Nevertheless, shoot N concentration vs aboveground biomass showed a typical decline in both treatments. In NLI, the shoot P concentration vs above-ground biomass relationship showed an increase in the early stages, indicating that P uptake and root-shoot competition for the absorbed P in the early plant stages controlled the establishment and the development of the leaf area.     

The effects of tree characteristics on rainfall interception in urban areas

Trees in urban areas have significant effects on the urban ecosystem. They can be used to improve the water cycle in urban areas by increasing evaporation and reducing runoff through rainfall interception. Street trees placed in planters on impervious areas reduce runoff by intercepting rainfall and by temporarily storing raindrops on leaves. Therefore, understanding tree canopy geometry and the effect of rainfall interception is important in urban hydrology. In this study, we assessed the effect of tree canopy morphology on rainfall interception using four major street tree species, Sophora japonica L., Ginkgo biloba L., Zelkova serrata (Thunb.) Makino, and Aesculus turbinata Blume, in Seoul, South Korea. We measured throughfall for each tree and also derived three-dimensional data of tree canopy morphology with a terrestrial laser scanner. Tree height, canopy crown width, leaf area index (LAI), leaf area density, mean leaf area, and mean leaf angle were used to determine canopy morphology. The interception rate was mostly affected by the LAI; a higher LAI tended to result in a higher interception rate. Leaf area affected the rainfall interception rate when trees had similar LAIs. These findings on individual tree canopy rainfall interception can help us to understand the importance of rainfall interception in hydrology and for ecological restoration when planning urban green spaces.

     

观赏灌木小枝和叶性状在林下庇荫环境中的权衡关系

小枝与叶片间的关系能够很好地反映植物对环境的适应策略。目前,从枝叶间权衡关系的角度研究树木对庇荫环境适应性的报道尚少,其中主要包括"生长-生长"权衡和"生长-生存"权衡两种假说。因此,为了探讨灌木在庇荫环境中,是否会在小枝和叶性状间采取权衡策略,来提高光照资源的利用能力或增强生存和防御能力,在城市绿地的林隙和林冠下两种光环境中,选择了没有人工修枝、整形等经营措施的金银木(Lonicera maackii)、小花溲疏(Deutzia parviflora)和连翘(Forsythia suspensa)等11种、79株观赏灌木作为研究对象,采集其当年生小枝,观测并计算了每棵灌木所处环境的有效光合辐射(PAR)相对累积光量和红光/远红光(R/FR),以及灌木的小枝干重(TDW)、单位小枝叶干重(LDW)、出叶强度(LN/TDW)、叶面积支持效率(LA/TDW)、比枝长(TL/TDW)和单叶面积(ILA) 6个性状。对数据进行标准化和数据转换后,运用Pearson相关检验分析光环境指标和灌木枝叶性状间的相关性;采用标准化主轴估计法进行异速生长方程的参数估计;使用多元回归分析不同光强下各性状的相互关系。结果表明:(1) PAR相对累积光量和R/FR与TDW和LDW呈极显著(P0.01或P0.001)正相关,与TL/TDW、LA/TDW、LN/TDW呈极显著(P0.001)负相关,与ILA相关性不显著(P 0.05)。整体上,R/FR与各灌木性状的相关性大于PAR相对累积光量;(2) TDW和LDW存在极显著(P0.001)的异速生长正相关关系。随着光强的减小,灌木当年生小枝和叶片的生物量都趋于减小,但是表现出相对偏向于叶片生物量的投资偏好;(3) LA/TDW和TL/TDW存在极显著(P0.001)的等速生长正相关关系。但随着光强的减小,比枝长随叶面积支持效率增加而增加的速率却减小,说明灌木在庇荫条件下,更倾向于采取忍耐型的光资源利用策略;(4) ILA和LN/TDW呈极显著(P0.001)异速生长负相关关系。随着光强的减小,灌木趋向于表现出单位小枝上着生大量小叶的现象。所以总体上,庇荫环境下的观赏灌木存在投资偏好和权衡,倾向于通过枝叶生长提高光截获能力来适应弱光环境,与"生长-生长"的权衡假说相符,但整体上,观赏灌木的耐阴性较差,故不建议种植在庇荫环境中。     

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.     

Anatomical and nutritional factors associated with susceptibility of elms (Ulmus spp.) to the elm leaf beetle (Coleoptera: Chrysomelidae)

A wide range of susceptibility exists across elm (Ulmus) species and hybrids to the elm leaf beetle, Pyrrhalta luteola (Müller) (Coleoptera: Chrysomelidae). We evaluated various elm species, hybrids, or cultivars (taxa) growing in an experimental plantation in the city of Holbrook, AZ, for leaf anatomical (toughness and trichome density) and nutritional (minerals and sugars) traits that may be associated with host resistance. Leaf toughness and percentage of defoliation (susceptibility) were not correlated. However, we found weak negative correlations between percentage of defoliation and density of trichomes on the leaf abaxial surface. Of the 11 leaf nutrients examined, concentrations of iron and phosphorus correlated inversely with percentage of defoliation. The remaining nine traits did not show any correlation with percentage of defoliation. We concluded that individual anatomical and nutritional traits of elm species/hybrids do not seem to create a strong barrier to elm leaf beetle defoliation. However, the results from a stepwise multiple regression analysis indicated that collectively, these traits may play an important role in determining susceptibility.