Resting sites, edge effects and dispersion of a polyphagous Bactrocera fruit fly within crops of different architecture

The spot or strip application of poisoned protein bait is a lure-and-kill technique used for the management of fruit flies. Knowledge of where flies occur in the crop environment is an important part of maximizing the efficacy of this tool. Bactrocera tryoni is a polyphagous pest of horticulture for which very little is known about its distribution within crops. With particular reference to edge effects, we monitored the abundance of B. tryoni in two crops of different architecture; strawberry and apple. In strawberries, we found more flies on the crop edge early in the fruiting season, which lessened gradually and eventually disappeared as the season progressed. In apple orchards, no such edge effect was observed and flies were found equally throughout the orchard. We postulated these differences may be due to differences in crop height (high vs. short) and/or crop canopy architecture (opened and branched in apple, dense and closed in strawberry). In a field cage trial, we tested these predictions using artificial plants of different height and canopy condition. Height and canopy structure type had no significant effects on fly oviposition and protein feeding, but the ‘apple’ type canopy significantly influenced resting. We thus postulate that there was an edge effect in strawberry because the crop was not providing resting sites and flies were doing so in vegetation around the field margins. The finding that B. tryoni shows different resting site preferences based on plant architecture offers the potential for strategic manipulation of the fly through specific border or inter-row plantings.

Resting sites, edge effects and dispersion of a polyphagous Bactrocera fruit fly within crops of different architecture

The spot or strip application of poisoned protein bait is a lure-and-kill technique used for the management of fruit flies. Knowledge of where flies occur in the crop environment is an important part of maximizing the efficacy of this tool. Bactrocera tryoni is a polyphagous pest of horticulture for which very little is known about its distribution within crops. With particular reference to edge effects, we monitored the abundance of B. tryoni in two crops of different architecture; strawberry and apple. In strawberries, we found more flies on the crop edge early in the fruiting season, which lessened gradually and eventually disappeared as the season progressed. In apple orchards, no such edge effect was observed and flies were found equally throughout the orchard. We postulated these differences may be due to differences in crop height (high vs. short) and/or crop canopy architecture (opened and branched in apple, dense and closed in strawberry). In a field cage trial, we tested these predictions using artificial plants of different height and canopy condition. Height and canopy structure type had no significant effects on fly oviposition and protein feeding, but the 'apple' type canopy significantly influenced resting. We thus postulate that there was an edge effect in strawberry because the crop was not providing resting sites and flies were doing so in vegetation around the field margins. The finding that B. tryoni shows different resting site preferences based on plant architecture offers the potential for strategic manipulation of the fly through specific border or inter-row plantings. © 2013 Blackwell Verlag GmbH.

A generic individual-based spatially explicit model as a novel tool for investigating insect-plant interactions: A case study of the behavioural ecology of frugivorous Tephritidae

Computational modelling of mechanisms underlying processes in the real world can be of great value in understanding complex biological behaviours. Uptake in general biology and ecology has been rapid. However, it often requires specific data sets that are overly costly in time and resources to collect. The aim of the current study was to test whether a generic behavioural ecology model constructed using published data could give realistic outputs for individual species. An individual-based model was developed using the Pattern-Oriented Modelling (POM) strategy and protocol, based on behavioural rules associated with insect movement choices. Frugivorous Tephritidae (fruit flies) were chosen because of economic significance in global agriculture and the multiple published data sets available for a range of species. The Queensland fruit fly (Qfly), Bactrocera tryoni, was identified as a suitable individual species for testing. Plant canopies with modified architecture were used to run predictive simulations. A field study was then conducted to validate our model predictions on how plant architecture affects fruit flies’ behaviours. Characteristics of plant architecture such as different shapes, e.g., closed-canopy and vase-shaped, affected fly movement patterns and time spent on host fruit. The number of visits to host fruit also differed between the edge and centre in closed-canopy plants. Compared to plant architecture, host fruit has less contribution to effects on flies’ movement patterns. The results from this model, combined with our field study and published empirical data suggest that placing fly traps in the upper canopy at the edge should work best. Such a modelling approach allows rapid testing of ideas about organismal interactions with environmental substrates in silico rather than in vivo, to generate new perspectives. Using published data provides a saving in time and resources. Adjustments for specific questions can be achieved by refinement of parameters based on targeted experiments.

Microhabitat use by Peucetia flava (Oxyopidae) on the glandular plant Rhyncanthera dichotoma (Melastomataceae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Onset of sheath extension and duration of lamina extension are major determinants of the response of maize lamina length to plant density

Background and Aims Plants regulate their architecture strongly in response to density, and there is evidence that this involves changes in the duration of leaf extension. This questions the approximation, central in crop models, that development follows a fixed thermal time schedule. The aim of this research is to investigate, using maize as a model, how the kinetics of extension of grass leaves change with density, and to propose directions for inclusion of this regulation in plant models. • Methods Periodic dissection of plants allowed the establishment of the kinetics of lamina and sheath extension for two contrasting sowing densities. The temperature of the growing zone was measured with thermocouples. Two-phase (exponential plus linear) models were fitted to the data, allowing analysis of the timing of the phase changes of extension, and the extension rate of sheaths and blades during both phases. • Key Results The duration of lamina extension dictated the variation in lamina length between treatments. The lower phytomers were longer at high density, with delayed onset of sheath extension allowing more time for the lamina to extend. In the upper phytomers—which were shorter at high density—the laminae had a lower relative extension rate (RER) in the exponential phase and delayed onset of linear extension, and less time available for extension since early sheath extension was not delayed. • Conclusions The relative timing of the onset of fast extension of the lamina with that of sheath development is the main determinant of the response of lamina length to density. Evidence is presented that the contrasting behaviour of lower and upper phytomers is related to differing regulation of sheath ontogeny before and after panicle initiation. A conceptual model is proposed to explain how the observed asynchrony between lamina and sheath development is regulated.

Simulating spray deposition on plant canopies within a wind tunnel

Three-dimensional computer modelling techniques are being used to develop a probabilistic model of turbulence-related spray transport around various plant architectures to investigate the influence of plant architectures and crop geometry on the sprayapplication process. Plant architecture models that utilise a set of growth rules expressed in the Lindenmayer systems (L-systems) formalism have been developed and programmed using L-studio software. Modules have been added to simulate the movement ofdroplets through the air and deposition on the plant canopy. Deposition of spray on an artificial plant structure was measured in the wind tunnel at the University of Queensland, Gatton campus and the results compared to the model simulation. Further trials are planned to measure the deposition of spray droplets on various crop and weed species and the results from these trials will be used to refine and validate the combined spray and plant architecture model.

Modeling Nymphoides architecture: A morphological analysis of Nymphoides aquatica (Menyanthaceae)

• Premise of the study: Species in the aquatic genus Nymphoides have inflorescences that appear to arise from the petioles of floating leaves. The inflorescence-floating leaf complex can produce vegetative propagules and/or additional inflorescences and leaves. We analyzed the morphology of N. aquatica to determine how this complex relates to whole plant architecture and whether whole plant growth is sympodial or monopodial. • Methods: We used dissections, measurements, and microscopic observations of field-collected plants and plants cultivated for 2 years in outdoor tanks in south Florida, USA. • Key results: Nymphoides aquatica had a submerged plagiotropic rhizome that produced floating leaves in an alternate/spiral phyllotaxy. Rhizomes were composed of successive sympodial units that varied in the number of leaves produced before the apex terminated. The basic sympodial unit had a prophyll that subtended a renewal-shoot bud, a short-petioled leaf (SPL) with floating lamina, and an inflorescence; the SPL axillary bud expanded as a vegetative propagule. Plants produced either successive basic sympodial units or expanded sympodia that intercalated long-petioled leaves between the prophyll and the SPL. • Conclusions: Nymphoides aquatica grows sympodially, forming a rhizome composed of successive basic sympodia and expanded sympodial units. Variations on these types of sympodial growth help explain the branching patterns and leaf morphologies described for other Nymphoides species. Monitoring how these two sympodial phases are affected by water depth provides an ecologically meaningful way to assess N. aquatica’s responses to altered hydrology.

Quantification of the effects of architectural traits on dry mass production and light interception of tomato canopy under different temperature regimes using a dynamic functional-structural plant model

There is increasing interest in evaluating the environmental effects on crop architectural traits and yield improvement. However, crop models describing the dynamic changes in canopy structure with environmental conditions and the complex interactions between canopy structure, light interception, and dry mass production are only gradually emerging. Using tomato (Solanum lycopersicum L.) as a model crop, a dynamic functional-structural plant model (FSPM) was constructed, parameterized, and evaluated to analyse the effects of temperature on architectural traits, which strongly influence canopy light interception and shoot dry mass. The FSPM predicted the organ growth, organ size, and shoot dry mass over time with high accuracy (>85%). Analyses of this FSPM showed that, in comparison with the reference canopy, shoot dry mass may be affected by leaf angle by as much as 20%, leaf curvature by up to 7%, the leaf length: width ratio by up to 5%, internode length by up to 9%, and curvature ratios and leaf arrangement by up to 6%. Tomato canopies at low temperature had higher canopy density and were more clumped due to higher leaf area and shorter internodes. Interestingly, dry mass production and light interception of the clumped canopy were more sensitive to changes in architectural traits. The complex interactions between architectural traits, canopy light interception, dry mass production, and environmental conditions can be studied by the dynamic FSPM, which may serve as a tool for designing a canopy structure which is 'ideal' in a given environment.

A comparison of techniques for the reconstruction of leaf surfaces from scanned data

The foliage of a plant performs vital functions. As such, leaf models are required to be developed for modelling the plant architecture from a set of scattered data captured using a scanning device. The leaf model can be used for purely visual purposes or as part of a further model, such as a fluid movement model or biological process. For these reasons, an accurate mathematical representation of the surface and boundary is required. This paper compares three approaches for fitting a continuously differentiable surface through a set of scanned data points from a leaf surface, with a technique already used for reconstructing leaf surfaces. The techniques which will be considered are discrete smoothing D2-splines [R. Arcangeli, M. C. Lopez de Silanes, and J. J. Torrens, Multidimensional Minimising Splines, Springer, 2004.], the thin plate spline finite element smoother [S. Roberts, M. Hegland, and I. Altas, Approximation of a Thin Plate Spline Smoother using Continuous Piecewise Polynomial Functions, SIAM, 1 (2003), pp. 208--234] and the radial basis function Clough-Tocher method [M. Oqielat, I. Turner, and J. Belward, A hybrid Clough-Tocher method for surface fitting with application to leaf data., Appl. Math. Modelling, 33 (2009), pp. 2582-2595]. Numerical results show that discrete smoothing D2-splines produce reconstructed leaf surfaces which better represent the original physical leaf.

Estimation of light interception in research environments: A joint approach using directional light sensors and 3D virtual plants applied to sunflower (Helianthus annuus) and Arabidopsis thaliana in natural and artificial conditions

Light interception is a major factor influencing plant development and biomass production. Several methods have been proposed to determine this variable, but its calculation remains difficult in artificial environments with heterogeneous light. We propose a method that uses 3D virtual plant modelling and directional light characterisation to estimate light interception in highly heterogeneous light environments such as growth chambers and glasshouses. Intercepted light was estimated by coupling an architectural model and a light model for different genotypes of the rosette species Arabidopsis thaliana (L.) Heynh and a sunflower crop. The model was applied to plants of contrasting architectures, cultivated in isolation or in canopy, in natural or artificial environments, and under contrasting light conditions. The model gave satisfactory results when compared with observed data and enabled calculation of light interception in situations where direct measurements or classical methods were inefficient, such as young crops, isolated plants or artificial conditions. Furthermore, the model revealed that A. thaliana increased its light interception efficiency when shaded. To conclude, the method can be used to calculate intercepted light at organ, plant and plot levels, in natural and artificial environments, and should be useful in the investigation of genotype-environment interactions for plant architecture and light interception efficiency. This paper originates from a presentation at the 5th International Workshop on Functional–Structural Plant Models, Napier, New Zealand, November 2007.

Induced Variations in Brassinosteroid Genes Define Barley Height and Sturdiness, and Expand the Green Revolution Genetic Toolkit

Reduced plant height and culm robustness are quantitative characteristics important for assuring cereal crop yield and quality under adverse weather conditions. A very limited number of short-culm mutant alleles were introduced into commercial crop cultivars during the Green Revolution. We identified phenotypic traits, including sturdy culm, specific for deficiencies in brassinosteroid biosynthesis and signaling in semidwarf mutants of barley (Hordeum vulgare). This set of characteristic traits was explored to perform a phenotypic screen of near-isogenic short-culm mutant lines from the brachytic, breviaristatum, dense spike, erectoides, semibrachytic, semidwarf, and slender dwarf mutant groups. In silico mapping of brassinosteroid-related genes in the barley genome in combination with sequencing of barley mutant lines assigned more than 20 historic mutants to three brassinosteroid-biosynthesis genes (BRASSINOSTEROID-6-OXIDASE, CONSTITUTIVE PHOTOMORPHOGENIC DWARF, and DIMINUTO) and one brassinosteroid-signaling gene (BRASSINOSTEROID-INSENSITIVE1 [HvBRI1]). Analyses of F2 and M2 populations, allelic crosses, and modeling of nonsynonymous amino acid exchanges in protein crystal structures gave a further understanding of the control of barley plant architecture and sturdiness by brassinosteroid-related genes. Alternatives to the widely used but highly temperature-sensitive uzu1.a allele of HvBRI1 represent potential genetic building blocks for breeding strategies with sturdy and climate-tolerant barley cultivars.

Auxin-Responsive OsMGH3, a Common Downstream Target of OsMADS1 and OsMADS6, Controls Rice Floret Fertility

GH3 proteins control auxin homeostasis by inactivating excess auxin as conjugates of amino acids and sugars and thereby controlling cellular bioactive auxin. Since auxin regulates many aspects of plant growth and development, regulated expression of these genes offers a mechanism to control various developmental processes. OsMGH3/OsGH3-8 is expressed abundantly in rice florets and is regulated by two related and redundant transcription factors, OsMADS1 and OsMADS6, but its contribution to flower development is not known. We functionally characterize OsMGH3 by overexpression and knock-down analysis and show a partial overlap in these phenotypes with that of mutants in OsMADS1 and OsMADS6. The overexpression of OsMGH3 during the vegetative phase affects the overall plant architecture, whereas its inflorescence-specific overexpression creates short panicles with reduced branching, resembling in part the effects of OsMADS1 overexpression. In contrast, the down-regulation of endogenous OsMGH3 caused phenotypes consistent with auxin overproduction or activated signaling, such as ectopic rooting from aerial nodes. Florets in OsMGH3 knock-down plants were affected in carpel development and pollen viability, both of which reduced fertility. Some of these floret phenotypes are similar to osmads6 mutants. Taken together, we provide evidence for the functional significance of auxin homeostasis and its transcriptional regulation during rice panicle branching and floret organ development.

Functions for rice RFL in vegetative axillary meristem specification and outgrowth

Roles for the transcription factor RFL in rice axillary meristem development were studied. Its regulatory effects on LAX1, CUC1, and OsPIN3 reveal its functions in axillary meristem specification and outgrowth.Axillary meristems (AMs) are secondary shoot meristems whose outgrowth determines plant architecture. In rice, AMs form tillers, and tillering mutants reveal an interplay between transcription factors and the phytohormones auxin and strigolactone as some factors that underpin this developmental process. Previous studies showed that knockdown of the transcription factor gene RFL reduced tillering and caused a very large decrease in panicle branching. Here, the relationship between RFL, AM initiation, and outgrowth was examined. We show that RFL promotes AM specification through its effects on LAX1 and CUC genes, as their expression was modulated on RFL knockdown, on induction of RFL:GR fusion protein, and by a repressive RFL-EAR fusion protein. Further, we report reduced expression of auxin transporter genes OsPIN1 and OsPIN3 in the culm of RFL knockdown transgenic plants. Additionally, subtle change in the spatial pattern of IR4 DR5:GFP auxin reporter was observed, which hints at compromised auxin transport on RFL knockdown. The relationship between RFL, strigolactone signalling, and bud outgrowth was studied by transcript analyses and by the tillering phenotype of transgenic plants knocked down for both RFL and D3. These data suggest indirect RFL-strigolactone links that may affect tillering. Further, we show expression modulation of the auxin transporter gene OsPIN3 upon RFL:GR protein induction and by the repressive RFL-EAR protein. These modified forms of RFL had only indirect effects on OsPIN1. Together, we have found that RFL regulates the LAX1 and CUC genes during AM specification, and positively influences the outgrowth of AMs though its effects on auxin transport.

OsLIC1基因参与水稻株型调控的功能研究

CCCH型锌指蛋白是进化上比较保守的一类锌指蛋白家族，其典型的氨基酸的基序为C-X7-8-C-X5-C-X3-H，其中X为任意氨基酸，这类锌指基序一般以重复的双拷贝形式存在。本论文克隆并鉴定了一个全新的、只含有一个CCCH型锌指基序的基因，利用反义RNA策略研究该基因功能，结果发现该基因的反义转基因植株表现出叶夹角增大的表型，因此我们将该基因命名为OsLIC1（Oryza sativa Lamina Increased Leaf Angle Control 1）。生物信息学分析发现该基因定位于水稻6号染色体近端粒的一端，位于BAC克隆AP004324中。OsLIC1与通常的CCCH型锌指蛋白含有多个重复的CCCH锌指基序不同，它只含有一个CCCH型锌指基序。除了CCCH锌指结构域以外，该蛋白在靠近C-端的位置还有一段丝氨酸（Ser）富集的区域，在此区域之前，还有一个在真核生物中相对保守的，以EELR为核心基序的结构域。采用基因枪将含OsLIC1-GFP融合构建的瞬时表达载体轰击入洋葱内表皮细胞，激光共聚焦显微镜观察发现OsLIC1-GFP可以定位到细胞核中。利用酵母转录激活系统发现以EELR为核心基序的结构域具有转录激活的功能。体外核酸结合活性分析显示OsLIC1蛋白可以结合双链DNA，这些结果证明OsLIC1是一个转录因子，这也是在植物中首次发现CCCH型锌指蛋白可以作为转录因子的方式调节基因的表达。 用玉米泛素启动子（Maize Ubiquitin promoter）驱动OsLIC1基因的反义表达载体转化水稻，获得的内源OsLIC1基因表达量下降的转基因植株表现出三个明显的表型：转基因植株的叶夹角增大;转基因的株高低于对照以及转基因植株的穗粒数减少。扫描电镜观察发现转基因植株叶夹角增大是由于近轴面细胞排列发生了改变以及维管束发育受阻引起的。转基因植株的Southern Blot和RT-PCR分析，结合Western Blot分析证明了转基因植株的表型与转基因事件之间的直接联系，并证明了转基因植株中内源OsLIC1在蛋白水平的确受到了抑制。采用RT-PCR技术、Promoter：：GUS和RNA in situ杂交三种方法相结合研究OsLIC1基因的表达模式，结果表明OsLIC1基因主要在叶颈、节以及分蘖原基中表达，这与转基因植株的表型相吻合，进一步证明了转基因植株的表型与基因功能之间的关系。Affymetrix 水稻全基因组芯片分析结果显示许多受油菜素内酯诱导表达的基因在转基因植株的叶颈材料中表达量上调，RT-PCR进一步验证了这一结果。由于在转基因植株中出现的叶夹角增大的表型和水稻油菜素内酯的作用相似，而基因芯片的结果又从分子水平提供了证据和线索。进一步采用RT-PCR和Promoter：：GUS相结合的方法研究OsLIC1基因对油菜素内酯的响应，结果发现OsLIC1基因可以被油菜素内酯诱导表达。而且，OsLIC1基因的反义转基因植株与野生型相比，表现出对油菜素内酯信号更敏感的响应。根据以上结果，推测OsLIC1可能是水稻油菜素内酯信号转导途径的负调控因子。水稻油菜素内酯合成和信号转导的突变体d2-1和d61-1具有直立的叶片的特征。用反义OsLIC1转基因植株以及野生型水稻与d2-1和d61-1突变体分别进行遗传杂交，结果发现在反义OsLIC1转基因植株与d2-1和d61-1突变体的杂交F1代中，都表现出叶夹角增大的表型。但是，在F2代中，在d2-1和d61-1纯合背景下，分别表现出叶夹角增大和叶片直立的表型，说明OsLIC1上位于d2-1，而d61-1则上位于OsLIC1。这一结果进一步证明了OsLIC1是通过参与水稻油菜素内酯信号调节而发挥对水稻叶夹角的调控作用。