Yaakov Goldwasser

Control of Orobanche crenata and Orobanche aegyptiaca in parsley

Abstract Parsley ( Petroselinum crispum ) is a host of the angiosperm root holoparasites Orobanche crenata and Orobanche aegyptiaca in the Mediterranean region and suffers heavy yield and quality losses. Eight field studies were performed to test the efficacy and selectivity of herbicides on Orobanche control in parsley. Initial experiments showed that the amino acid inhibiting herbicides imazapic and glyphosate did not affect the parsley crop and provided excellent Orobanche control. The efficacy of these herbicides was further tested by single and split post-emergence application at different geographical locations, in spring–summer (warm) and fall–winter (cold) growing seasons and on different Orobanche species. Finally the efficiency of tank mix and alternating application of these herbicides was studied. O. crenata and O. aegyptiaca were completely controlled by split foliar application of imazapic at 2.5– 5.0 g / ha or glyphosate 36– 72 g / ha , applied on 5–7 leaf parsley before the first cutting and on the young new growth after each cutting. At the low rates herbicides were parsley-safe, but higher rates caused slight crop damage. Split applications of low rates of the two herbicides as a tank mixture were safe to parsley and achieved effective Orobanche control. Herbicide mixtures and alternating applications are important in inhibiting or delaying the development of herbicide-resistance in weeds including parasitic plants. The findings of this study propose efficient, selective, low cost and easy to apply herbicides for control of Orobanche in parsley.

Broomrape (Orobanche cumana) Control in Sunflower (Helianthus annuus) with Imazapic1

Abstract: Field trials were conducted in 1997 and 1998 at two locations in Israel to evaluate the efficacy of imazapic applied postemergence (POST) to sunflower for broomrape control under irrigated and nonirrigated conditions. Two sequential treatments of imazapic at 1.5 followed by (FB) 3.0, 3.0 FB 4.5, or 4.5 FB 6.0 g ai/ha on sunflower plants 12 ± 3 and 55 ± 5 cm tall, respectively, reduced sunflower broomrape throughout the growing season under irrigated and nonirrigated conditions. Sunflower growth was not affected by imazapic treatments. It was confirmed, in accordance with an earlier report, that when sequential treatments of imazapic included an application at the sunflower inflorescence developmental stage, the herbicide decreased seed yield in proportion to the applied rate. Nomenclature: Imazapic; broomrape, Orobanche cumana Waller; sunflower, Helianthus annuus L. Additional index words: Parasitic weed, herbicide. Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence.

Differential induction of Orobanche seed germination by Arabidopsis thaliana.

Parasitic plants, including the root holoparasites Orobanche spp., cause devastating damage to crops worldwide. Arabidopsis thaliana (L.) is widely used an amenable model for the study of plant biology, including plant-pathogen interactions. Bringing the two plants together in a controlled system will enable the study of the molecular and genetic basis involved in host-parasitic plant interactions and should provide tools for the detection of genes responsible for incompatibility and resistance responses. The objective of this study was to screen Arabidopsis lines for reduced germination of Orobanche seeds. A 96-cell well bioassay was developed to test the potential of lines, ecotypes and mutants of Arabidopsis to induce germination of Orobanche. Screening of 50 A. thaliana ecotypes did not reveal non-inducing ecotypes. Screening of 13000 A. thaliana fast neutron mutated M2 plants detected 94 non-inducing mutant plants of which 34 were rescued, self pollinated, and M3 seeds collected. M3 seedlings from five lines were reduced in their ability to induce germination. In a separate assay, we determined that the reduced germination rates corresponded with reduced distance from the roots at which germination occurred. While further studies are necessary to determine the segregation of low germination phenotypes, these lines might prove useful for studying the genetic basis of variation in germination stimulant production in A. thaliana.

Arabidopsis thaliana susceptibility to Orobanche spp

Abstract Parasitic plants, including the root holoparasites Orobanche spp., cause devastating damage to crops worldwide. Arabidopsis thaliana is widely used as an amenable model plant system to study host–pathogen interactions. Understanding the molecular basis involved in host–parasite interactions will provide practical tools for the detection of genes responsible for incompatibility and resistance responses. In preliminary petri dish experiments, A. thaliana induced seed germination of O. aegyptiaca, O. minor, and O. ramosa at the rate of 87, 72, and 67% of maximum seed germination, respectively. Arabidopsis thaliana induction of O. crenata and O. cumana seeds was negligible (less than 2% of maximum germination). In additional polyethylene bag studies, A. thaliana was parasitized by O. aegyptiaca, O. ramosa, and O. minor resulting in 12, 5, and 2 parasites per host plant, respectively. The results facilitate the use of A. thaliana in host-parasitic plant interaction research. Nomenclature: Orobanche aegyptiaca Pers. ORAAE, Egyptian broomrape; Orobanche crenata Forsk. ORACR, crenate broomrape; Orobanche cumana = Orobanche cernua Loefl. ORACE, nodding broomrape; Orobanche minor Sm. ORAMI, small broomrape; Orobanche ramosa L. ORARA, branched broomrape; Arabidopsis thaliana (L.) Heynh. ARBTH ‘Columbia’, mouse-ear cress.

Egyptian Broomrape (Orobanche aegyptiaca) Control in Tomato with Sulfonylurea Herbicides—Greenhouse Studies1

Broomrapes (Orobanche spp.) are root holoparasitic plants that cause severe damage to economically important crops, especially in Mediterranean countries. Egyptian broomrape is the most troublesome weed on tomatoes grown for processing in Israel. In the present study, we tested the efficacy and selectivity of four sulfonylurea herbicides in controlling Egyptian broomrape on tomatoes grown in pots under greenhouse conditions. MON 37500, rimsulfuron, HOE 404 and SL-160 were applied postemergence (POST) and preplant incorporated (PPI) followed by POST applications. MON 37500 and rimsulfuron were more selective to tomato and controlled the parasite more effectively than HOE 404 and SL-160. MON 37500 and rimsulfuron at 50 and 100 g ai/ha and at 100, 150, and 200 g ai/ha, respectively, applied on tomato foliage 14, 28, and 42 d after planting (DAP) and followed by sprinkler irrigation to field capacity, resulted in complete control of the parasite. However, a significant reduction in control efficacy was observed when the experiment was repeated with charcoal-topped pots, suggesting that the herbicides act mainly through the soil. Except for rimsulfuron, the PPI followed by two POST treatments was more phytotoxic to tomato plants than the POST treatments. The PPI plus POST applications controlled Egyptian broomrape effectively, but tomato plants were injured by HOE 404 at all PPI application rates and by MON 37500 at the high rate at 150 g/ha. The present study determined that three POST applications or a PPI application followed by two POST applications of MON 37500 at 50 or 100 g/ha, or rimsulfuron at 100, 150, or 200 g/ha were effective and selective in controlling Egyptian broomrape on tomato, under greenhouse conditions. Nomenclature: HOE 404, 2-ethoxyphenyl [[(4,6-dimethoxy-2-pyrimidinyl) amino]carbonyl]sulfamate; MON 37500, N-[[(4,6-dimethoxy-2-pyrimidinyl) amino] carbonyl]-2-(ethylsulfonyl)imidazo[1,2-a]pyridine-3-sulfonamide; rimsulfuron; SL-160, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino] carbonyl]-3-(trifluoromethyl)-2-pyridinesulfonamide; Egyptian broomrape, Orobanche aegyptiaca Pers. #3 ORAAE; tomato, Lycopersicon esculentum Mill. Additional index words: Activated charcoal, Orobanche control, parasitic weeds. Abbreviations: DAP, days after planting; POST, postemergence; PPI, preplant incorporated.

Tolerance of tomato varieties to lespedeza dodder

Abstract Dodder (Cuscuta) species are obligate shoot parasites that attach to stems and leaves of plants belonging to diverse families, diverting water, minerals, and metabolites, resulting in suppression of crop plants and yield reduction. Lespedeza dodder has the most diverse and numerous host range among the Cuscuta genus and is a major weed problem in tomato production in certain parts of the world, including California. At present, few resistant varieties of normally susceptible plant species have been developed or identified, and none are available in California. In this study, greenhouse and field studies were conducted to test and characterize the tolerance of commercial hybrid tomato varieties to lespedeza dodder. In greenhouse studies, Heinz varieties ‘9492’, ‘9553’, and ‘9992’ exhibited tolerance to the parasite, compared to the susceptible variety, ‘Halley 3155’. Lespedeza dodder germinated, made contact, twined around tomato stems, and adhered to them, but in most cases, haustoria failed to penetrate into the stem, eventually leading to the death of the parasite. In field studies, lespedeza dodder attachments were 75% less on tolerant varieties, and dodder growth was reduced by more than 70%. Nomenclature: Lespedeza dodder, Cuscuta pentagona Engelm. CVCPE; tomato, Lycopersicon esculentum L. ‘Heinz 9492’, ‘Heinz 9553’, ‘Heinz 9992’.

The Potential of Sulfosulfuron to Control Troublesome Weeds in Tomato1

There are few efficient and cost-effective methods for controlling weeds in processing tomatoes. Sulfosulfuron is a sulfonylurea herbicide developed for controlling weeds in wheat. In previous studies, we have demonstrated the efficacy of sulfosulfuron in selectively controlling Orobanche aegyptiaca in tomato. The objective of the present study was to elucidate the potential of sulfosulfuron to selectively control troublesome, nonparasitic weeds in tomato. In the greenhouse, sulfosulfuron efficacy at 37.5, 75.0, and 112.5 g ai/ha applied preplant incorporated (PPI), preemergence (PRE), and postemergence (POST) was tested. Sulfosulfuron when applied PPI and POST was highly selective in controlling weeds without causing injury to tomato. The weeds that were efficiently controlled, even at low rates of application, included purple nutsedge, black nightshade, mustard, pigweed, and bindweed. PRE application resulted in the most efficient weed control but was phytotoxic to tomato at high rates. Nomenclature: Sulfosulfuron; black nightshade, Solanum nigrum L. #3 SOLNI; field bindweed, Convolvulus arvensis L., # CONAR; purple nutsedge, Cyperus rotundus L. # CYPRO; redroot pigweed, Amaranthus retroflexus L. # AMARE; tomato, Lycopersicon esculentum Mill. # LYPES; wheat, Triticum aestivum L.; wild mustard, Sinapis arvensis L. # SINAR. Additional index words: Acetolactate synthase inhibitors, sulfonylurea herbicides, weed management. Abbreviations: ALS, acetolactate synthase; DAA, days after application; DAP, days after planting; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

The Use of Arabidopsis to Study Interactions between Parasitic Angiosperms and Their Plant Hosts

Abstract Parasitic plants invade host plants in order to rob them of water, minerals and nutrients. The consequences to the infected hosts can be debilitating and some of the worlds most pernicious agricultural weeds are parasitic. Parasitic genera of the Scrophulariaceae and Orobanchaceae directly invade roots of neighboring plants via underground structures called haustoria. The mechanisms by which these parasites identify and associate with host plants present unsurpassed opportunities for studying chemical signaling in plant-plant interactions. Seeds of some parasites require specific host factors for efficient germination, thereby insuring the availability of an appropriate host root prior to germination. A second set of signal molecules is required to induce haustorium development and the beginning of heterotrophy. Later stages in parasitism also require the presence of host factors, although these have not yet been well characterized. Arabidopsis is being used as a model host plant to identify genetic loci associated with stimulating parasite germination, haustorium development, and parasite support. Arabidopsis is also being employed to explore how host plants respond to parasite attack. Current methodologies and recent findings in Arabidopsis – parasitic plant interactions will be discussed.

Tolerance of parsley varieties to Orobanche

Abstract Parasitic plants infest numerous plants throughout the world depleting them of nutrients, minerals and water. Orobanche species are chlorophyll-lacking root holoparasites that cause severe damage to broad-leaved crops. Orobanche aegyptiaca and Orobanche crenata parasitize field, vegetable, fodder, flower and herb crops in the Mediterranean region. Curled parsley ( Petroselinum crispum ), a major crop in the dry herb industry in Israel, is highly susceptible to O. aegyptiaca and O. crenata and in infested fields suffers severe yield and quality damage. An in vitro study in polyethylene bags, greenhouse experiments in soil-filled pots and trials in a naturally Orobanche -infested field were performed in order to screen and test for differential susceptibility of parsley varieties to O. aegyptiaca and O. crenata . Results revealed that the parsley varieties Garland and Garbo were tolerant to Orobanche compared to the susceptible varieties Darki, Extra Triple and Kaderava.

Field Dodder (Cuscuta campestris)—A New Model Describing Temperature-Dependent Seed Germination

Abstract 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.