The Domestication of Crop Plants
; Encyclopedia of Applied Plant Sciences; 2016; Vol. 3, pp. 50-54. Publisher's VersionAbstract
Food production economies based on domesticated plants and livestock is a relatively recent phenomenon in the human career. Packages of nutritionally and agronomically balanced crop plants evolved independently in several world regions including sub-Saharan Africa, Meso-America, North-east America, East Asia, and the Near East. The longest research tradition on the origins of agriculture concerning the Near East on which we elaborate. Geobotanical and ecological evidence on the wild progenitors in conjunction with archaeological and archaeobotanical data of the Near Eastern crop package species enable the reconstruction of this major event in the prehistory of humankind. The accumulated evidence from the Near East suggests a geographically focused/centered, and knowledge-based domestication of a suite of cereals and grain legume crops. Genetic and agronomic considerations enable to draw a distinction between the crucial traits underlying the domestication episode and traits that were selected for by farmers during the millennia following (under) domestication. This distinction is valuable for both reconstructing prehistoric events and for future crop improvement. © 2017 Elsevier Ltd. All rights reserved.
In vitro reconstruction and analysis of evolutionary variation of the tomato acylsucrose metabolic network
. Proceedings of the National Academy of Sciences of the United States of America 2016
, E239-E248. Publisher's VersionAbstract
Plant glandular secreting trichomes are epidermal protuberances that produce structurally diverse specialized metabolites, including medically important compounds. Trichomes of many plants in the nightshade family (Solanaceae) produce O-acylsugars, and in cultivated and wild tomatoes these are mixtures of aliphatic esters of sucrose and glucose of varying structures and quantities documented to contribute to insect defense. We characterized the first two enzymes of acylsucrose biosynthesis in the cultivated tomato Solanum lycopersicum. These are type I/IV trichome-expressed BAHD acyltransferases encoded by Solyc12g006330-or S. lycopersicum acylsucrose acyltransferase 1 (Sl-ASAT1)-and Solyc04g012020 (Sl-ASAT2). These enzymes were used.in concert with two previously identified BAHD acyltransferases. to reconstruct the entire cultivated tomato acylsucrose biosynthetic pathway in vitro using sucrose and acyl-CoA substrates. Comparative genomics and biochemical analysis of ASAT enzymes were combined with in vitro mutagenesis to identify amino acids that influence CoA ester substrate specificity and contribute to differences in types of acylsucroses that accumulate in cultivated andwild tomato species. This work demonstrates the feasibility of the metabolic engineering of these insecticidal metabolites in plants and microbes.
A new advanced backcross tomato population enables high resolution leaf QTL mapping and gene identification
. G3: Genes, Genomes, Genetics 2016
3169-3184. Publisher's VersionAbstract
Quantitative Trait Loci (QTL) mapping is a powerful technique for dissecting the genetic basis of traits and species differences. Established tomato mapping populations between domesticated tomato (Solanum lycopersicum) and its more distant interfertile relatives typically follow a near isogenic line (NIL) design, such as the S. pennellii Introgression Line (IL) population, with a single wild introgression per line in an otherwise domesticated genetic background. Here, we report on a new advanced backcross QTL mapping resource for tomato, derived from a cross between the M82 tomato cultivar and S. pennellii. This so-called Backcrossed Inbred Line (BIL) population is comprised of a mix of BC2 and BC3 lines, with domesticated tomato as the recurrent parent. The BIL population is complementary to the existing S. pennellii IL population, with which it shares parents. Using the BILs, we mapped traits for leaf complexity, leaflet shape, and flowering time. We demonstrate the utility of the BILs for fine-mapping QTL, particularly QTL initially mapped in the ILs, by fine-mapping several QTL to single or few candidate genes. Moreover, we confirm the value of a backcrossed population with multiple introgressions per line, such as the BILs, for epistatic QTL mapping. Our work was further enabled by the development of our own statistical inference and visualization tools, namely a heterogeneous hidden Markov model for genotyping the lines, and by using state-of-the-art sparse regression techniques for QTL mapping. © 2016 Fulop et al.
Farewell to the Lose–Lose Reality of Policing Plant Imports
. PLoS Biology 2016
. Publisher's VersionAbstract
In an age of free international shipments of mail-ordered seeds and plants, more policing will not stop the global migration of hitchhiking pests. The solution is in a preemptive response based on an internationally coordinated genomic deployment of global biodiversity in the largest breeding project since the “Garden of Eden.” This plan will enrich the narrow genetic basis of annual and perennial plants with adaptations to changing environments and resistances to the pests of the future. © 2016 Dani Zamir.
Fruit carotenoid-deficient mutants in tomato reveal a function of the plastidial isopentenyl diphosphate isomerase (IDI1) in carotenoid biosynthesis
. Plant Journal 2016
, 82-94. Publisher's VersionAbstract
Isoprenoids consist of a large class of compounds that are present in all living organisms. They are derived from the 5C building blocks isopentenyl diphosphate (IDP) and its isomer dimethylallyl diphosphate (DMADP). In plants, IDP is synthesized in the cytoplasm from mevalonic acid via the MVA pathway, and in plastids from 2-C-methyl-d-erythritol-4-phosphate through the MEP pathway. The enzyme IDP isomerase (IDI) catalyzes the interconversion between IDP and DMADP. Most plants contain two IDI enzymes, the functions of which are characteristically compartmentalized in the cells. Carotenoids are isoprenoids that play essential roles in photosynthesis and provide colors to flowers and fruits. They are synthesized in the plastids via the MEP pathway. Fruits of Solanum lycopersicum (tomato) accumulate high levels of the red carotene lycopene. We have identified mutations in tomato that reduce overall carotenoid accumulation in fruits. Four alleles of a locus named FRUIT CAROTENOID DEFICIENT 1 (fcd1) were characterized. Map-based cloning of fcd1 indicated that this gene encodes the plastidial enzyme IDI1. Lack of IDI1 reduced the concentration of carotenoids in fruits, flowers and cotyledons, but not in mature leaves. These results indicate that the plastidial IDI plays an important function in carotenoid biosynthesis, thus highlighting its role in optimizing the ratio between IDP and DMADP as precursors for different downstream isoprenoid pathways. © 2016 The Authors The Plant Journal © 2016 John Wiley & Sons Ltd
Evaluation of seasonal water use and crop coefficients for 'Cabernet Sauvignon' grapevines as the base for skilled regulated deficit irrigation
. Acta Horticulturae 2016
, 33-39. Publisher's VersionAbstract
Water consumption of wine grapevines (Vitis vinifera 'Cabernet Sauvignon') was measured during three consecutive growing seasons (2012-2014) using 6 drainage lysimeters. The lysimeters (1.5 m3 each) were installed within a two-hectare commercial vineyard in a Mediterranean region in the central mountain region of Israel. Water consumption of the lysimeter-grown vines (ETc) was measured daily and reference evapotranspiration (ETo) was calculated from regional meteorological data according to the Penman Monteith equation. Seasonal curves of crop coefficient (Kc) were calculated as Kc = ETc/ETo. Maximum ETc values (weekly average) in different seasons ranged from 7.5 to 6.64 mm day-1 and seasonal ETc (from DOY 99 through DOY 288) ranged from 746 to 780 mm over the growing seasons. Leaf area index (LAI) was measured weekly using the SunScan Canopy Analysis System. Maximum LAI ranged from 1.36 to 1.16 m2 m-2 for the 2012-2013 seasons, the seasonal LAI pattern was quite similar to control vines grown in the surrounding vineyard. A linear curve relating Kc to LAI (R2 values ranged from 0.76 to 0.85) is proposed as the basis for efficient irrigation management. Some of the differences in ETc and Kc values that were observed are different from those obtained in table grapes (Williams et al., 2003; Netzer et al., 2009) and wine grapes (Picón-Toro et al., 2012) is explained by the different canopy size and architecture.
Phosphorous nutritional level, carbohydrate reserves and flower quality in olives
. PLoS ONE 2016
. Publisher's VersionAbstract
The olive tree is generally characterized by relatively low final fruit set consequential to a significant rate of undeveloped pistils, pistil abortion, and flower and fruitlet abscission. These processes are acknowledged to be governed by competition for resources between the developing vegetative and reproductive organs. To study the role of phosphorus (P) nutritional level on reproductive development, trees were grown under four levels of P for three years in large containers. Phosphorus nutritional level was positively related to rate of reproductive bud break, inflorescence weight, rate of hermaphrodite flowers, pistil weight, fruitlet persistence, fruit set and the consequential total number of fruits. The positive impact of P nutrition on the productivity parameters was not related to carbohydrate reserves or to carbohydrate transport to the developing inflorescence. Phosphorous deficient trees showed significant impairment of assimilation rate, and yet, carbohydrates were accumulated in inflorescences at levels comparable to or higher than trees receiving high P. In contrast to female reproductive organs, pollen viability was consistently higher in P deficient trees, possibly due to the enhanced carbohydrate availability. Overall, the positive effect of P on female reproductive development was found to be independent of the total carbohydrate availability. Hence, P is speculated to have a direct influence on reproductive processes. © 2016 Erel et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
De novo transcriptome sequencing and development of abscission zone-specific microarray as a new molecular tool for analysis of tomato organ abscission
. Frontiers in Plant Science 2016
. Publisher's VersionAbstract
Abscission of flower pedicels and leaf petioles of tomato (Solanum lycopersicum) can be induced by flower removal or leaf deblading, respectively, which leads to auxin depletion, resulting in increased sensitivity of the abscission zone (AZ) to ethylene. However, the molecular mechanisms that drive the acquisition of abscission competence and its modulation by auxin gradients are not yet known. We used RNA-Sequencing (RNA-Seq) to obtain a comprehensive transcriptome of tomato flower AZ (FAZ) and leaf AZ (LAZ) during abscission. RNA-Seq was performed on a pool of total RNA extracted from tomato FAZ and LAZ, at different abscission stages, followed by de novo assembly. The assembled clusters contained transcripts that are already known in the Solanaceae (SOL) genomics and NCBI databases, and over 8823 identified novel tomato transcripts of varying sizes. An AZ-specific microarray, encompassing the novel transcripts identified in this study and all known transcripts from the SOL genomics and NCBI databases, was constructed to study the abscission process. Multiple probes for longer genes and key AZ-specific genes, including antisense probes for all transcripts, make this array a unique tool for studying abscission with a comprehensive set of transcripts, and for mining for naturally occurring antisense transcripts. We focused on comparing the global transcriptomes generated from the FAZ and the LAZ to establish the divergences and similarities in their transcriptional networks, and particularly to characterize the processes and transcriptional regulators enriched in gene clusters that are differentially regulated in these two AZs. This study is the first attempt to analyze the global gene expression in different AZs in tomato by combining the RNA-Seq technique with oligonucleotide microarrays. Our AZ-specific microarray chip provides a cost-effective approach for expression profiling and robust analysis of multiple samples in a rapid succession. © 2016 Sundaresan, Philosoph-Hadas, Riov, Mugasimangalam, Kuravadi, Kochanek, Salim, Tucker and Meir.
Detection and Differentiation of Potato Virus Y Strains by Melting Analysis of an Oligonucleotide Virus Probe
. American Journal of Potato Research 2016
, 620-625. Publisher's VersionAbstract
A novel simple, fast qualitative method for detection and differentiation of PVY strains in potatoes by the LightCycler technology is described. Fluorescent-labeled probe designed to contain variable degree of homology with a ‘target sequence’ of several known reference PVY strains was annealed to PCR products of these viruses followed by a graded melting analysis. The specific characteristics of the melting curves enable the detection, distinction and differentiation of each of following four known PVY strains O-FL, O-RB, N and NTN, in a single reaction obviating the need for size or nucleotide sequence analyses. In addition, it was demonstrated that virus extracts from plants infected with more than one strain can be resolved using this procedure. The melting-curves of extracts from 55 market size tubers harvested randomly from commercial fields and compared with those of the reference virus strains, revealed the presence of O-FL, O-RB and NTN strains of PVY. © 2016, The Potato Association of America.
Physiology of Domesticated Alliums: Onions, Garlic, Leek, and Minor Crops
; Encyclopedia of Applied Plant Sciences; 2016; Vol. 3, pp. 255-261. Publisher's VersionAbstract
More than 50 species of the genus Allium have been cultivated worldwide for sustenance, flavor, and medicinal purposes, as well as for ornamentals, from the tropics to the temperate zone. In most alliums, intact tissues contain odorless, nonvolatile sulfur-containing molecules that upon cells' disruption break down enzymatically to form volatile flavor compounds that are responsible for the characteristic odor and taste of these species. The genetic makeup, photoperiod, and both storage and growth temperatures are the main factors controlling bulbing and florogenesis in these plant species. The most common Allium food crops are bulb onion garlic, leek, shallot, chives, and Welsh onion. Most fertile cultivated alliums are raised from seed, transplants, or sets. However, some sterile species, such as garlic, elephant garlic, rocambole tree onion, topsetting onions, and shallot are propagated vegetatively. During millennia of cultivation, no natural co-evolution with biotic and abiotic agents has taken place. Hence, most cultivated alliums lack many important traits, including resistance to pests and environmental stresses. Current efforts and employment of both classical and novel tools for genetic and plant physiology studies are expected to accelerate improvements in terms of distribution, yield, and quality of these important crops. © 2017 Elsevier Ltd. All rights reserved.
; Encyclopedia of Applied Plant Sciences; 2016; Vol. 3, pp. 39-44. Publisher's VersionAbstract
A concise description of the history, classification, cytology, and botany of potato is presented. The effects of the environment on the morphology, physiology, and development of the potato plant and the adverse effects of high temperatures, drought, and salinity on growth, tuber development, and tuber quality are described. Tuber dormancy and its control in association with storage and with 'seed' tubers' vigor are discussed. Principles of crop production, storage, and tuber quality are presented. © 2017 Elsevier Ltd. All rights reserved.
Few multiyear precipitation-reduction experiments find a shift in the productivity-precipitation relationship
. Global change biology 2016
, 2570-2581. Publisher's VersionAbstract
Well-defined productivity-precipitation relationships of ecosystems are needed as benchmarks for the validation of land models used for future projections. The productivity-precipitation relationship may be studied in two ways: the spatial approach relates differences in productivity to those in precipitation among sites along a precipitation gradient (the spatial fit, with a steeper slope); the temporal approach relates interannual productivity changes to variation in precipitation within sites (the temporal fits, with flatter slopes). Precipitation-reduction experiments in natural ecosystems represent a complement to the fits, because they can reduce precipitation below the natural range and are thus well suited to study potential effects of climate drying. Here, we analyse the effects of dry treatments in eleven multiyear precipitation-manipulation experiments, focusing on changes in the temporal fit. We expected that structural changes in the dry treatments would occur in some experiments, thereby reducing the intercept of the temporal fit and displacing the productivity-precipitation relationship downward the spatial fit. The majority of experiments (72%) showed that dry treatments did not alter the temporal fit. This implies that current temporal fits are to be preferred over the spatial fit to benchmark land-model projections of productivity under future climate within the precipitation ranges covered by the experiments. Moreover, in two experiments, the intercept of the temporal fit unexpectedly increased due to mechanisms that reduced either water loss or nutrient loss. The expected decrease of the intercept was observed in only one experiment, and only when distinguishing between the late and the early phases of the experiment. This implies that we currently do not know at which precipitation-reduction level or at which experimental duration structural changes will start to alter ecosystem productivity. Our study highlights the need for experiments with multiple, including more extreme, dry treatments, to identify the precipitation boundaries within which the current temporal fits remain valid. © 2016 John Wiley & Sons Ltd.
Seedling emergence and phenotypic response of common bean germplasm to different temperatures under controlled conditions and in open field
. Frontiers in Plant Science 2016
. Publisher's VersionAbstract
Rapid and uniform seed germination and seedling emergence under diverse environmental conditions is a desirable characteristic for crops. Common bean genotypes (Phaseolus vulgaris L.) differ in their low temperature tolerance regarding growth and yield. Cultivars tolerant to low temperature during the germination and emergence stages and carriers of the grain quality standards demanded by consumers are needed for the success of the bean crop. The objectives of this study were (i) to screen the seedling emergence and the phenotypic response of bean germplasm under a range of temperatures in controlled chamber and field conditions to display stress-tolerant genotypes with good agronomic performances and yield potential, and (ii) to compare the emergence of bean seedlings under controlled environment and in open field conditions to assess the efficiency of genebanks standard germination tests for predicting the performance of the seeds in the field. Three trials were conducted with 28 dry bean genotypes in open field and in growth chamber under low, moderate, and warm temperature. Morpho-agronomic data were used to evaluate the phenotypic performance of the different genotypes. Cool temperatures resulted in a reduction of the rate of emergence in the bean genotypes, however, emergence and early growth of bean could be under different genetic control and these processes need further research to be suitably modeled. Nine groups arose from the Principal Component Analysis (PCA) representing variation in emergence time and proportion of emergence in the controlled chamber and in the open field indicating a trend to lower emergence in large and extra-large seeded genotypes. Screening of seedling emergence and phenotypic response of the bean germplasm under a range of temperatures in controlled growth chambers and under field conditions showed several genotypes, as landraces 272, 501, 593, and the cultivar Borlotto, with stress-tolerance at emergence, and high yield potential that could be valuable genetic material for breeding programs. Additionally, the potential genetic erosion in genebanks was assessed. Regarding bean commercial traits, under low temperature at sowing time seed reached larger size, and crop yield was higher compared to warmer temperatures at the sowing time. Therefore, early sowing of bean is strongly recommended. © 2016 De Ron, Rodiño, Santalla, González, Lema, Martín and Kigel.
Targeted grazing of milk thistle (Silybum marianum) and Syrian thistle (Notobasis syriaca) by goats: Preference following preconditioning, generational transfer, and toxicity
. Applied Animal Behaviour Science 2016
, 53-59. Publisher's VersionAbstract
Nitrophilic thistles such as milk thistle (Sylibum marianum) and Syrian thistle (Notobasis syriaca) encroach rangeland areas where animals gather and defecate, in particular around watering and feeding points. High densities of milk and Syrian thistles (MST) diminish forage yields and detract from the amenity value of these areas. The aims of the present study were: (i) to test the safety of feeding MST to adult goats; (ii) to determine if preconditioning adult goats to MST, by feeding it indoors together with concentrate, enhances preference for MST when they graze MST-rich pastures; and (iii) to test for generational transfer by comparing the propensity to consume MST and the preference for MST over clover hay for weaned kids that previously suckled from does that were, or were not, preconditioned to consume MST fed as green fodder. We found that eating MST was not toxic to adult goats. Over six observation sessions of one hour, preconditioned goats devoted 50% more time to consuming MST than non-conditioned counterparts (30.3% versus 20.6%, respectively; P = 0.0005), and kids that experienced the preconditioning period together with their does tended (P = 0.08) to show a greater preference for MST over clover hay than their counterparts born to non-conditioned adults. Although the efficacy in depleting the seed bank has yet to be verified, from the point of view of the animal, goats may be used in targeted grazing of milk and Syrian thistles. © 2016 Elsevier B.V.
Climate change increases the risk of herbicide-resistant weeds due to enhanced detoxification
. Planta 2016
, 1217-1227. Publisher's VersionAbstract
Main conclusion: Global warming will increase the incidence of metabolism-based reduced herbicide efficacy on weeds and, therefore, the risk for evolution of non-target site herbicide resistance. Climate changes affect food security both directly and indirectly. Weeds are the major biotic factor limiting crop production worldwide, and herbicides are the most cost-effective way for weed management. Processes associated with climatic changes, such as elevated temperatures, can strongly affect weed control efficiency. Responses of several grass weed populations to herbicides that inhibit acetyl-CoA carboxylase (ACCase) were examined under different temperature regimes. We characterized the mechanism of temperature-dependent sensitivity and the kinetics of pinoxaden detoxification. The products of pinoxaden detoxification were quantified. Decreased sensitivity to ACCase inhibitors was observed under elevated temperatures. Pre-treatment with the cytochrome-P450 inhibitor malathion supports a non-target site metabolism-based mechanism of herbicide resistance. The first 48 h after herbicide application were crucial for pinoxaden detoxification. The levels of the inactive glucose-conjugated pinoxaden product (M5) were found significantly higher under high- than low-temperature regime. Under high temperature, a rapid elevation in the level of the intermediate metabolite (M4) was found only in pinoxaden-resistant plants. Our results highlight the quantitative nature of non-target-site resistance. To the best of our knowledge, this is the first experimental evidence for temperature-dependent herbicide sensitivity based on metabolic detoxification. These findings suggest an increased risk for the evolution of herbicide-resistant weeds under predicted climatic conditions. © 2016, Springer-Verlag Berlin Heidelberg.
Developing Global Leaders for Research, Regulation, and Stewardship of Crop Protection Chemistry in the 21st Century
. Journal of Agricultural and Food Chemistry 2016
, 52-60. Publisher's VersionAbstract
To provide sufficient food and fiber to the increasing global population, the technologies associated with crop protection are growing ever more sophisticated but, at the same time, societal expectations for the safe use of crop protection chemistry tools are also increasing. The goal of this perspective is to highlight the key issues that face future leaders in crop protection, based on presentations made during a symposium titled "Developing Global Leaders for Research, Regulation and Stewardship of Crop Protection Chemistry in the 21st Century", held in conjunction with the IUPAC 13th International Congress of Pesticide Chemistry in San Francisco, CA, USA, during August 2014. The presentations highlighted the fact that leaders in crop protection must have a good basic scientific training and understand new and evolving technologies, are aware of the needs of both developed and developing countries, and have good communication skills. Concern is expressed over the apparent lack of resources to meet these needs, and ideas are put forward to remedy these deficiencies. © 2015 American Chemical Society.
Factors Affecting Egyptian Broomrape (Orobanche aegyptiaca) Control in Carrot
. Weed Science 2016
, 321-330. Publisher's VersionAbstract
Carrot is a high-value cash crop that is grown in Israel throughout the year. Egyptian broomrape is a chlorophyll-lacking, obligate, root holoparasite that parasitizes members of many botanical families, including the Apiaceae. At high infestation levels, Egyptian broomrape can cause total yield loss in carrot. A protocol has been developed for the control of Egyptian broomrape in carrot. Because carrots are grown in Israel under fall, winter, and spring conditions, information about the relations between the efficacy of control and temperature is important. Therefore, the objective of this study was to investigate the response of carrot and Egyptian broomrape to herbicides at different phenological stages under varying temperature regimes. This study was conducted under temperature-controlled conditions in a multiclimate greenhouse and in a net house. Applications of the imidazolinone herbicides imazapic and imazamox (each applied at 4.8 g ai ha-1) injured carrot plants and reduced yield and yield quality. Glyphosate effectively controlled Egyptian broomrape and did not negatively affect the carrot plants when applied three times at ≤-108 g ae ha-1. High temperatures increased the carrot plants' sensitivity to glyphosate. This study found that three applications of glyphosate at 108 g ae ha-1 can prevent Egyptian broomrape damage without causing any damage to the carrot crop. Our results indicate that weather conditions can affect herbicide phytotoxicity in carrot. The highest temperature at the time of herbicide application corresponded to the strongest observed phytotoxic effect. To summarize, effective Egyptian broomrape control can be achieved by three sequential foliar applications of glyphosate (108 g ae ha-1), beginning during the early parasitism stage (i.e., small tubercles). Moreover, applying glyphosate on carrot at high temperature (i.e., 28/22 C day/night temperatures) can injure carrot plants and reduce control efficacy. Nomenclature: Glyphosate; imazamox; imazapic; Egyptian broomrape, Orobanche aegyptiaca Pers. ORAAE; carrot, Daucus carota L. var. sativus Hoffm. © 2016 Weed Science Society of America.
Field Dodder (Cuscuta campestris)–A New Model Describing Temperature-Dependent Seed Germination
. Weed Science 2016
, 53-60. Publisher's VersionAbstract
The members of the genus Cuscuta (common name: dodder) are obligate holoparasitic plants that are found throughout the agricultural regions of the world. Of all of the species of dodder, field dodder (Cuscuta campestris) causes the most damage to crops. This species parasitizes the shoots of broadleaf plant crops and weeds. We conducted a series of field dodder seed germination tests in controlled-temperature chambers, in order to describe the effect of temperature on field dodder germination and develop a germination model based on the obtained data. The best fit was obtained when temperature data and time were transformed to thermal time using the beta-function model. The field dodder germination model can serve as a tool for knowledge-based predictions of germination and emergence timing, to allow for the implementation of effective mechanical and chemical management measures. Nomenclature: Field dodder; Cuscuta campestris Yuncker. © 2016 Weed Science Society of America.
From sensitivity to resistance - factors affecting the response of Conyza spp. to glyphosate
. Pest management science 2016
, 1681-1688. Publisher's VersionAbstract
BACKGROUND: Conyza bonariensis and C. canadensis are troublesome weeds, particularly in fields with minimum tillage, on roadsides and in perennial crops. The distribution of these difficult-to-control species is further increased by the spread of glyphosate-resistant populations. A preliminary investigation has demonstrated the existence of various degrees of glyphosate tolerance/resistance in these populations, underscoring the need to examine the relationship between glyphosate efficacy and plant growth conditions. RESULTS: In populations exposed to glyphosate at different temperatures, glyphosate tolerance increased linearly as the temperature was increased, whereas when grown under the same temperatures, they largely responded similarly to the herbicide. Furthermore, the sensitivity of plants to glyphosate decreased significantly with plant age and increased following temporal exposure to shading. Dose-response studies confirmed the glyphosate resistance of four C. bonariensis populations that were 8-30 times more resistant to glyphosate than the most glyphosate-sensitive population. These populations retained their characteristic glyphosate resistance even under unfavourable growth conditions. CONCLUSION: These findings indicate that the effect of glyphosate on both Conyza species is strongly linked to growing conditions. This has great importance for our understanding of glyphosate resistance and for control of these weeds in agricultural systems. © 2015 Society of Chemical Industry. © 2015 Society of Chemical Industry.