Ragweed species (Ambrosia spp.) in Israel: distribution and allergenicity
. Aerobiologia 2019
, 85-95. Publisher's VersionAbstract
Ambrosia, specifically Ambrosia artemisiifolia, are known throughout the world as invasive, allergenic and noxious weeds. This research leads to the first map of the spread of Ambrosia species in Israel and describes the risk associated with their distribution to the public health. Six Ambrosia species were identified in Israel. There is one invasive species, A. confertiflora DC (Burr ragweed), which is most abundant in central Israel. There are three naturalized species: A. tenuifolia Spreng (Lacy ragweed) which is found in several locations; A. psilostachya DC (Cuman ragweed) and A. grayi (woolly leaf bur ragweed), which are restricted to a single location each. There are two casual species: A. artemisiifolia L. (short ragweed, common ragweed) and A. trifida L. (Giant ragweed). There are pronounced and clear differences between the species in their life cycle, morphology and phenology, which may explain the level of invasion of each one in Israel. The causes of the invasion are mainly anthropogenic. Many populations of Ambrosia are found near fishponds and animal feed centers, indicating that ragweed seeds feasibly arrived to Israel in grain shipments. Human sensitization to local pollen extracts of A. confertiflora and A. tenuifolia was studied by skin test reaction and compared with commercial extracts of A. artemisiifolia and A. trifida. Patient’s response was three times stronger in A. confertiflora with respect to the other three species. The rapid dissemination of A. confertiflora, the manner in which its pollen is dispersed and its allergenic potential indicate risks to public health. © 2018, Springer Nature B.V.
Selective and effective control of field dodder (Cuscuta campestris) in chickpea with granular pendimethalin
. Weed Technology 2019
, 586-594. Publisher's VersionAbstract
Field dodder is an obligatory stem and leaf plant parasite that causes significant damage in field and vegetable crops in all agricultural regions of the globe. Selective and effective measures to control the parasite are extremely limited. In recent studies, we have shown that granular formulations of dinitroaniline cell division-inhibiting herbicides applied after crop establishment and before dodder germination fit our dodder control strategy and kill the parasite effectively and selectively. The aim of our study conducted from 2014 to 2018 was to evaluate the efficacy and selectivity of granular pendimethalin for dodder control in chickpea under laboratory, greenhouse, and field conditions. Petri dish experiments revealed that the herbicide reduces dodder seed germination while its main effect is a restriction of shoot elongation. Greenhouse experiments demonstrated that the inhibition and distortion of dodder shoot growth impede shoot twining and prevent attachment to the host plant. In dose-response experiments conducted in the greenhouse, we observed that half the recommended rate of granular pendimethalin provides efficient dodder control with no damage to chickpea seedlings. In 3 yr of chickpea field trials, GPM applied across the seeding bed at the recommended rate resulted in high crop yields that were not significantly different from those observed for the untreated no-dodder control, while half of the recommended dose efficiently controlled dodder and other weeds with no damage to the crop, resulting in significantly increased chickpea yields and profitability. These studies indicate that GPM can provide efficient and selective dodder control in chickpea. © Weed Science Society of America, 2019.
; Handbook of Flowering: Volume I; 2018; pp. 427-433. Publisher's VersionAbstract
Amaranthus is a genus of tropical origin that belongs to the Amaranthaceae. Today it is widely distributed all over the world, with species reaching temperate regions even before man converted some of them into cosmopolitan weeds or domesticates (crops or ornamentals).15 About 60 species are native to the Americas, and about 15 others to Europe, Asia, Africa, and Australia. Most of them are pioneer annuals of naturally open habitats, producing abundant seed. They thrive by constant colonization of sites of disturbed soil, with full sun and little competition. Long natural selection for such a way of life preadaptated certain of the species for success in habitats drastically disturbed by man. Thus, today Amaranthus spp. are best known as noxious weeds (e.g., A. hybridus L., A. retroflexus L., A. spinosus L., A. powellii S. Wats.). However, in tropical and subtropical countries, certain species are grown for grain (A. hypocondriacus L., A. cruentus L., A. caudatus L.), whereas the young plants of others are eaten as pot-herbs (A. dubius Mart., A. tricolor L.). Other species are cultivated as ornamentals for their highly colored inflorescence (A. caudatus L.) or leaves (A. tricolor L.). © 1995 by CRC Press, Inc.
Application Timing and Degradation Rate of Sulfosulfuron in Soil Co-affect Control Efficacy of Egyptian broomrape (Phelipanche aegyptiaca) in Tomato
. Weed Science 2018
, 780-788. Publisher's VersionAbstract
Egyptian broomrape (Phelipanche aegyptiaca Pers.) is a root-parasitic weed that severely damages many crops worldwide, including tomato (Solanum lycopersicum L.). In Israel, the management protocol used for P. aegyptiaca in open-field tomato includes PPI sulfosulfuron at 37.5 g ai ha-1 to the top 10-cm soil layer. The objective of this study was to investigate the co-effect of sulfosulfuron application timing and variable degradation rate in soil on the control efficacy of P. aegyptiaca in tomato. Degradation of sulfosulfuron (80ng g-1 soil) at a temperature of 15C, measured in soil samples from three farms using liquid chromatography-tandem mass spectrometry, followed a first-order kinetics with variable degradation rate constant among sites (0.008 to 0.012 d-1). Incubation at 25 C increased sulfosulfuron degradation rate constant by a factor of 2 to 2.7 in soils from the different sites, with a similar degradation rate order among soils. A higher degradation rate in the soil resulted in a shorter period of residual activity, measured using a sorghum [Sorghum bicolor (L.) Moench.] bioassay. Phelipanche aegyptiaca management in open-field tomatoes was investigated in five independent field experiments. Sulfosulfuron soil concentration throughout the growing season (following preplant incorporation of 37.5 g ha-1) was calculated from laboratory-measured degradation rates, which were corrected to represent the effect of recorded temperatures at each field. At the end of the tomato growing season, control efficacy of P. aegyptiaca varied among experiments (70.4% to 100%) and positively correlated with predicted sulfosulfuron concentration at the critical period for seedling control (R2=0.67). The current study confirms that sulfosulfuron is degraded in soil to nonphytotoxic metabolites and that rapid degradation rates would result in reduced injury to P. aegyptiaca seedling and, consequently, lower control efficacy. © Weed Science Society of America, 2018.
Effects of environmental conditions on the fitness penalty in herbicide resistant brachypodium hybridum
. Frontiers in Plant Science 2017
. Publisher's VersionAbstract
Herbicide-resistance mutations may impose a fitness penalty in herbicide-free environments. Moreover, the fitness penalty associated with herbicide resistance is not a stable parameter and can be influenced by ecological factors. Here, we used two Brachypodium hybridum accessions collected from the same planted forest, sensitive (S) and target-site resistance (TSR) to photosystem II (PSII) inhibitors, to study the effect of agro-ecological parameters on fitness penalty. Both accessions were collected in the same habitat, thus, we can assume that the genetic variance between them is relatively low. This allow us to focus on the effect of PSII TSR on plant fitness. S plants grains were significantly larger than those of the TSR plants and this was associated with a higher rate of germination. Under low radiation, the TSR plants showed a significant fitness penalty relative to S plants. S plants exhibiting dominance when both types of plants were grown together in a low-light environment. In contrast to previous documented studies, under high-light environment our TSR accession didn’t show any significant difference in fitness compared to the S accession. Nitrogen deficiency had significant effect on the R compared to the S accession and was demonstrated in significant yield reduction. TSR plants also expressed a high fitness penalty, relative to the S plants, when grown in competition with wheat plants. Two evolutionary scenarios can be suggested to explain the coexistence of both TSR and S plants in the same habitat. The application of PSII inhibitors may have created selective pressure toward TSR dominancy; termination of herbicide application gave an ecological advantage to S plants, creating changes in the composition of the seed bank. Alternatively, the high radiation intensities found in the Mediterranean-like climate may reduce the fitness penalty associated with TSR. Our results may suggest that by integrating non-herbicidal approaches into weed-management programs, we can reduce the agricultural costs associated with herbicide resistance. © 2017 Frenkel, Matzrafi, Rubin and Peleg.
Four Ambrosia species in Israel: Invasive, naturalized and casual alien plants
. Israel Journal of Plant Sciences 2017
, 93-98. Publisher's VersionAbstract
Four Ambrosia species are currently identified in Israel: The invasive perennial species Ambrosia confertiflora DC., the naturalized perennial species Ambrosia tenuifolia Spreng. and Ambrosia psilostachya DC., and the casual annual species Ambrosia artemisiifolia L. In this study, we performed a comparative analysis of three species: A. confertiflora, A. tenuifolia, and A. artemisiifolia. We found differences in morphology, growth and flowering phenology and physiology that may explain, besides climatic constraints, the factors involved in the differing invasion status of these species in Israel. A. artemisiifolia and A. confertiflora use strategies typical of invasive species: Rapid growth and regeneration, phenotypic plasticity and reproductive ability. These characteristics have enabled the spread of A. confertiflora in Israel. However, A. artemisiifolia has not become established in Israel due to the country's dry summers. The naturalized populations have survived in ecological niches in Israel for many years, but due to their slow growth and low numbers of viable achenes, they have not spread. © 2017 by Koninklijke Brill NV, Leiden, The Netherlands.
Herbicidal Activity of Monoterpenes Is Associated with Disruption of Microtubule Functionality and Membrane Integrity
. Weed Science 2017
, 19-30. Publisher's VersionAbstract
Aromatic plants and their volatile compounds affect seed germination and plant growth, and therefore hold potential for agriculture uses as plant growth regulators and bioherbicides. In the present study 17 major monoterpenes were selected, and their mechanisms of plant toxicity were elucidated using transgenic Arabidopsis thaliana at various growth stages. Microtubulin and the plant cell membrane were identified as the focal targets through which phytotoxicity and herbicidal activity acted. Variability in monoterpene mechanisms was observed. Limonene and (+)-citronellal had strong antimicrotubule efficacy, whereas citral, geraniol, (-)-menthone, (+)-carvone, and (-)-citronellal demonstrated moderate antimicrotubule efficacy. Pulegone, (-)-carvone, carvacrol, nerol, geranic acid, (+)/(-)-citronellol, and citronellic acid lacked antimicrotubule capacity. An enantioselective disruption of microtubule assembly was recorded for (+)/(-)-citronellal and (+)/(-)-carvone. The (+) enatiomers were more potent than their (-) counterparts. Citral, limonene, carvacrol, and pulegone were also tested for phytotoxicity and herbicidal activity. Pulegone had no detectable effect on microtubules or membranes. Citral disrupted microtubules but did not cause membrane damage. Carvacrol lacked a detectable effect on microtubules but incited membrane leakage, and limonene disrupted microtubules and membrane leakage. Therefore, only limonene was herbicidal at the tested concentrations. In planta quantification of residues revealed that citral was biotransformed into nerol and geraniol, and limonene was converted into carvacrol, which could explain its dual capacity with respect to microtubules and membrane functionality. The results obtained are an important added value to commercial efforts in selecting appropriate aromatic plants to be sources of bioherbicidal compounds for sustainable weed management with a limited potential for herbicide resistance evolution in weed populations. Nomenclature: Arabidopsis thaliana, citral, limonene, pulegone, carvacrol. © Weed Science Society of America, 2016.
Isoxadifen safening mechanism in sweet corn genotypes with differential response to P450-metabolized herbicides
. Pesticide Biochemistry and Physiology 2017
, 22-28. Publisher's VersionAbstract
Three sweet corn genotypes, two inbred lines (IBER001 and IBER002) and their hybrid (ER00X), differ in their phenotypic responses to several P450-metabolized herbicides, used in sweet corn, namely, foramsulfuron, iodosulfuron, rimsulfuron and tembotrione. Foramsulfuron is a sulfonylurea herbicide commonly formulated with the safener isoxadifen that is used for selective post-emergence weed control in corn. Our goal was to elucidate the mechanism of these genotypes’ responses to foramsulfuron and safener isoxadifen and examine the heritability of those responses. IBER001 was sensitive to foramsulfuron + isoxadifen, with an ED50 of 3.6 g ai ha− 1, while IBER002 and ER00X were tolerant with ED50 values of 808 and 700 g ai ha− 1, respectively. ALS enzyme extracted from each of the different genotypes was equally sensitive to foramsulfuron. Pre-treatment with malathion, a known cytochrome P450 inhibitor, increased foramsulfuron injury in IBER002 and ER00X, but had no effect on those lines when isoxadifen was applied with the herbicide. Foramsulfuron-treated IBER001 was severely injured regardless of the presence of malathion and/or isoxadifen. Pre-treatment with malathion similarly increased the phytotoxicity of iodosulfuron + safener (mefenpyr) and rimsulfuron to the tolerant genotypes, but did not increase the level of injury caused by the tembotrione + isoxadifen treatment. Segregation of F2 and backcross progenies according to their responses to foramsulfuron + isoxadifen revealed a pattern of inheritance typical of a trait controlled by a single gene inheritance, with a recessive allele conferring sensitivity. Our results support the hypothesis that foramsulfuron selectivity is associated with P450 metabolism and that isoxadifen positively affects P450 activity. The sensitive genotype that does not respond to isoxadifen is presumably homozygous for a deficient or non-functioning P450 gene. © 2017 Elsevier Inc.
Non-target-site glyphosate resistance in Conyza bonariensis is based on modified subcellular distribution of the herbicide
. Pest Management Science 2017
, 246-253. Publisher's VersionAbstract
BACKGROUND: Conyza spp. were the first broadleaf weeds reported to have evolved glyphosate resistance. Several mechanisms have been proposed for glyphosate resistance. In an effort to elucidate the mechanism of this resistance in Conyza bonariensis, possible target-site and non-target-site mechanisms were investigated in glyphosate-resistant (GR) C. bonariensis biotypes. RESULTS: Using differential glyphosate applications and analyses of shikimate accumulation, we followed the herbicide effect in different plant organs and monitored the herbicide's apparent mobility. We found high shikimate levels in the roots and young leaves of glyphosate-sensitive (GS) plants, regardless of the site of application, whereas in GR plants, shikimate accumulated mainly in treated young leaves. 14C-glyphosate studies, however, revealed the expected source-to-sink translocation pattern in both GS and GR plants. Sequencing of the appropriate EPSPS DNA fragments of GR and GS plants revealed no alteration at the Pro106 position. CONCLUSION: These data support the hypothesis that the glyphosate resistance of our C. bonariensis GR biotypes is associated with altered subcellular distribution of glyphosate, which keeps the herbicide sequestered away from the EPSPS target site in the chloroplast. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry
Secondary Effects of Glyphosate Action in Phelipanche aegyptiaca: Inhibition of Solute Transport from the Host Plant to the Parasite
. Frontiers in Plant Science 2017
255. Publisher's VersionAbstract
It is currently held that glyphosate efficiently controls the obligate holoparasite Phelipanche aegyptiaca (Egyptian broomrape) by inhibiting its endogenous shikimate pathway, thereby causing a deficiency in aromatic amino acids (AAA). While there is no argument regarding the shikimate pathway being the primary site of the herbicide's action, the fact that the parasite receives a constant supply of nutrients, including proteins and amino acids, from the host does not fit with an AAA deficiency. This apparent contradiction implies that glyphosate mechanism of action in P. aegyptiaca is probably more complex and does not end with the inhibition of the AAA biosynthetic pathway alone. A possible explanation would lie in a limitation of the translocation of solutes from the host as a secondary effect. We examined the following hypotheses: (a) glyphosate does not affects P. aegyptiaca during its independent phase and (b) glyphosate has a secondary effect on the ability of P. aegyptiaca to attract nutrients, limiting the translocation to the parasite. By using a glyphosate-resistant host plant expressing the “phloem-mobile” green fluorescent protein (GFP), it was shown that glyphosate interacts specifically with P. aegyptiaca, initiating a deceleration of GFP translocation to the parasite within 24 h of treatment. Additionally, changes in the entire sugars profile (together with that of other metabolites) of P. aegyptiaca were induced by glyphosate. In addition, glyphosate did not impair germination or seedling development of P. aegyptiaca but begun to exert its action only after the parasite has established a connection to the host vascular system and became exposed to the herbicide. Our findings thus indicate that glyphosate does indeed have a secondary effect in P. aegyptiaca, probably as a consequence of its primary target inhibition—via inhibition of the translocation of phloem-mobile solutes to the parasite, as was simulated by the mobile GFP. The observed disruption in the metabolism of major sugars that are abundant in P. aegyptiaca within 48 h after glyphosate treatment provides a possible explanation for this inhibition of translocation and might reflect a critical secondary effect of the herbicide's primary action that results in loss of the parasite's superior sink for solutes.
Unraveling the Transcriptional Basis of Temperature-Dependent Pinoxaden Resistance in Brachypodium hybridum
. Frontiers in Plant Science 2017
1064. Publisher's VersionAbstract
Climate change endangers food security and our ability to feed the ever-increasing human population. Weeds are the most important biotic stress, reducing crop-plant productivity worldwide. Chemical control, the main approach for weed management, can be strongly affected by temperature. Previously, we have shown that temperature-dependent non-target site (NTS) resistance of Brachypodium hybridum is due to enhanced detoxification of acetyl-CoA carboxylase inhibitors. Here, we explored the transcriptional basis of this phenomenon. Plants were characterized for the transcriptional response to herbicide application, high-temperature and their combination, in an attempt to uncover the genetic basis of temperature-dependent pinoxaden resistance. Even though most of the variance among treatments was due to pinoxaden application (61%), plants were able to survive pinoxaden application only when grown under high-temperatures. Biological pathways and expression patterns of members of specific gene families, previously shown to be involved in NTS metabolic resistance to different herbicides, were examined. Cytochrome P450, glucosyl transferase and glutathione-S-transferase genes were found to be up-regulated in response to pinoxaden application under both control and high-temperature conditions. However, biological pathways related to oxidation and glucose conjugation were found to be significantly enriched only under the combination of pinoxaden application and high-temperature. Analysis of reactive oxygen species (ROS) was conducted at several time points after treatment using a probe detecting H2O2/peroxides. Comparison of ROS accumulation among treatments revealed a significant reduction in ROS quantities 24 h after pinoxaden application only under high-temperature conditions. These results may indicate significant activity of enzymatic ROS scavengers that can be correlated with the activation of herbicide-resistance mechanisms. This study shows that up-regulation of genes related to metabolic resistance is not sufficient to explain temperature-dependent pinoxaden resistance. We suggest that elevated activity of enzymatic processes at high-temperature may induce rapid and efficient pinoxaden metabolism leading to temperature-dependent herbicide resistance.
Different Mutations Endowing Resistance to Acetyl-CoA Carboxylase Inhibitors Results in Changes in Ecological Fitness of Lolium rigidum Populations
. Frontiers in Plant Science 2017
1078. Publisher's VersionAbstract
Various mutations altering the herbicide target site (TS), can lead to structural modifications that decrease binding efficiency and results in herbicide resistant weed. In most cases, such a mutation will be associated with ecological fitness penalty under herbicide free environmental conditions. Here we describe the effect of various mutations, endowing resistance to acetyl-CoA carboxylase (ACCase) inhibitors, on the ecological fitness penalty of Lolium rigidum populations. The TS resistant populations, MH (substitution of isoleucine 1781 to leucine) and NO (cysteine 2088 to arginine), were examined and compared to a sensitive population (AL). Grain weight (GW) characterization of individual plants from both MH and NO populations, showed that resistant individuals had significantly lower GW compared with sensitive ones. Under high temperatures, both TS resistant populations exhibited lower germination rate as compared with the sensitive (AL) population. Likewise, early vigor of plants from both TS resistant populations was significantly lower than the one measured in plants of the sensitive population. Under crop-weed intra-species competition, we found an opposite trend in the response of plants from different populations. Relatively to inter-population competition conditions, plants of MH population were less affected and presented higher reproduction abilities compared to plants from both AL and NO populations. On the basis of our results, a non-chemical approach can be taken to favor the sensitive individuals, eventually leading to a decline in resistant individuals in the population.
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.
Thermal time model for egyptian broomrape (Phelipanche aegyptiaca) parasitism dynamics in carrot (daucus carota L.): Field validation
. Frontiers in Plant Science 2016
. Publisher's VersionAbstract
Carrot, a highly profitable crop in Israel, is severely damaged by Phelipanche aegyptiaca parasitism. Herbicides can effectively control the parasite and prevent damage, but for optimal results, knowledge about the soil–subsurface phenological stage of the parasite is essential. Parasitism dynamics models have been successfully developed for the parasites P. aegyptiaca, Orobanche cumana, and Orobanche minor in the summer crops, tomato, sunflower, and red clover, respectively. However, these models, which are based on a linear relationship between thermal time and the parasitism dynamics, may not necessarily be directly applicable to the P. aegyptiaca–carrot system. The objective of the current study was to develop a thermal time model to predict the effect of P. aegyptiaca parasitism dynamics on carrot growth. For development and validation of the models, data was collected from a temperature-controlled growth experiment and from 13 plots naturally infested with P. aegyptiaca in commercial carrot fields. Our results revealed that P. aegyptiaca development is related to soil temperature. Moreover, unlike P. aegyptiaca parasitism in sunflower and tomato, which could be predicted both a linear model, P. aegyptiaca parasitism dynamics on carrot roots required a nonlinear model, due to the wider range of growth temperatures of both the carrot and the parasite. Hence, two different nonlinear models were developed for optimizing the prediction of P. aegyptiaca parasitism dynamics. Both models, a beta function model and combined model composed of a beta function and a sigmoid curve, were able to predict first P. aegyptiaca attachment. However, overall P. aegyptiaca dynamics was described more accurately by the combined model (RMSE = 14.58 and 10.79, respectively). The results of this study will complement previous studies on P. aegyptiaca management by herbicides to facilitate optimal carrot growth and handling in fields infested with P. aegyptiaca. © 2016 Cochavi, Rubin, Achdari and Eizenberg.
Mechanism of glyphosate control of Phelipanche aegyptiaca
, 1095 - 1107. Publisher's VersionAbstract
Despite its total reliance on its host plant, the holoparasitePhelipanche aegyptiacasuffers from a deficiency of aromatic amino acids upon exposure to glyphosate.