Parasitic Orobanche Research Articles

A Putative Role for Fusaric Acid in Biocontrol of the Parasitic Angiosperm Orobanche ramosa

Fusarium spp. are ubiquitous fungi found in soil worldwide as both pathogenic and nonpathogenic strains. The signals leading to disease or the absence of disease are poorly understood. We recently showed that fusaric acid (FA), a nonspecific toxin produced by most Fusarium spp., could elicit various plant defense responses at 100 nM without toxic effect. In this study, we checked for the effect of FA on root and root hairs, probable first site of contact between the fungi and the host. Large FA concentrations reduce root and root-hair growth and induce a rapid transient membrane hyperpolarization, followed by a large depolarization, due to the inhibition of H(+)-ATPase currents. Nanomolar concentrations of FA induced only an early transient membrane hyperpolarization of root hairs compatible with the induction of a signal transduction pathway. FA at 10(-7) M failed to induce salicylic acid- and jasmonic acid/ethylene-dependent defense-related genes but inhibited the germination of the angiosperm parasite Orobanche ramosa in contact of FA-pretreated Arabidopsis thaliana seedlings. These data suggest that FA at nontoxic concentrations could activate signal transduction components necessary for plant-defense responses that could contribute to biocontrol activity of Fusarium spp.

A new method for in-situ monitoring of the underground development of Orobanche cumana in sunflower (Helianthus annuus) with a mini-rhizotron.

To develop an in-situ, non-destructive method for observation and monitoring of the underground developmental stages of the root parasite Orobanche cumana. The parasitic weed Orobanche causes severe damage to vegetables and field crops. Most of the damage caused to the crops occurs during the underground, unobservable parasitism stage. Sunflower (Helianthus annuus 'Adi') plants were planted in soil that was artificially inoculated with O. cumana seeds. Clear Plexiglas mini-rhizotron plastic observation tubes were inserted into the soil. Seed germination, early stage of penetration, and formation of tubercles and spikes were observed non-destructively and were monitored throughout the growing season by mean of a mini-rhizotron camera. Use of this technology enabled the complete individual parasite life cycle from the very early development (including germination) to Orobanche shoot to be monitored. In addition, the effect of the systemic herbicide Cadre (imazapic) on the development of O. cumana was inspected and quantified. This novel methodology facilitates the in-situ study of major aspects of the host-parasite interaction and of parasite suppression, such as parasitism dynamics, parasite growth rate, and the effect of chemical treatments on the parasite.

OPINION: Are pectinolytic activities of Orobanche cumana seedlings related to virulence towards sunflower?

Using a host differential screening method in pot and in hydroponic co-cultures, four populations of the sunflower root parasite Orobanche cumana Wallr. were studied for their pathogenicity against seven sunflower genotypes that are thought to carry specific resistance genes. These broomrape populations, which belong to three supposed races (D, E, and F), were observed to differ by their virulence. The Spanish supposed-race F population was the most virulent, showing the greatest number of Orobanche fixations and biomass reduction on sunflower genotypes resistant to the other tested populations (Romanian supposed-race D population and both Spanish and Bulgarian supposed-race E populations). However, from the differential screening none of the sunflowers was absolutely immune to all populations of broomrape since at least a few broomrape attachments, which sometimes became necrosed, were observed during some weeks on the most resistant roots. However, typical hypersensitive response was not observed on the host roots, whose exudates stimulate germination of all four O. cumana populations to the same extent, but with some variations depending on the sunflower genotypes. Before attachment, Orobanche seedlings released cell-wall-degrading enzymes such as pectin methylesterase (PME, EC 3.1.1.11) and polygalacturonase (PG, EC 3.2.1.15). These pectinolytic activities were higher in the most virulent and recently discovered race F.

Defense Gene Expression Analysis of Arabidopsis thaliana Parasitized by Orobanche ramosa

ABSTRACT The infection of Arabidopsis thaliana roots with the obligate parasite Orobanche ramosa represents a useful model for a study of the molecular events involved in the host plant response to a parasitic plant attack. To avoid analysis problems due to the subterranean development of O. ramosa, we developed two in vitro co-culture systems: O. ramosa seedlings infesting Arabidopsis plantlet roots and callus tissues. We were then able to investigate the expression patterns of some host plant genes selected among genes known to be involved in metabolic pathways and resistance mechanisms activated during several plant-pathogen interactions including ethylene, isoprenoid, phenylpropanoid, and jasmonate biosynthesis pathways, oxidative stress responses, and pathogenesis-related proteins. Molecular analyses were carried out using polymerase chain reaction amplification methods allowing semiquantitative evaluation of transcript accumulation during early (first hours) and late (15 days) stages of infestation, in whole roots or parts close to the parasite attachment site. In A. thaliana, O. ramosa induced most of the general response signaling pathways in a transient manner even before its attachment to A. thaliana roots. However, no salicylic acid-dependent defense is observed because no activation of systemic acquired resistance markers is detectable, whereas genes, co-regulated by jasmonate and ethylene, do display enhanced expression.

Developing genetic variability in sunflower (Helianthus annuus L) by combined use of hybridization with gamma radiation or ultrasound

As a result of hybridization between the Bulgarian fertility restorer line R 2574 and mixed pollen from a polycross population of known genetic composition, and treatment of immature embryos with gamma radiation or ultrasound, a large number of new fertility restorer lines were developed. Lines R 114, R 115, and R 116, subjected to investigation in this study, are characterized with significant changes concerning most of the studied characters. The increased number of seeds per head in lines R 115 and R 116 the increased 1000 seed weight in line R 114, the 100% resistance to the parasite Orobanche in lines R 114 and R 116, and the very good combining ability in hybridization are the desired combination in the breeding program of sunflower. The hybrids Rada and 80, developed with the participation of lines R 114 and R 116, considerably exceeded the mean standard (the Bulgarian commercial hybrids Albena and Super Start) in seed and oil yields simultaneously possessing high resistance to the Orobanche population of races distributed in Bulgaria. In 2002, the hybrid Rada was registered for testing by State Variety Testing Commission and it exceeded the mean standard of the country. The combined use of interlinear hybridization with physical mutagenesis or ultrasound and the embryo culture method leads to increased genetic variability in sunflower and to a considerable shortening of the breeding process, producing 5 generations within a single year.

Transformation of carrots with mutant acetolactate synthase for Orobanche (broomrape) control.

Parasitic Orobanche spp are major constraints to vegetable crop production in the Mediterranean basin (to eastern Europe) and in localized places in India, China and the USA. Transgenic target-site herbicide resistance (eg, to acetolactate synthase inhibitors) allows for movement of unmetabolized herbicide through the crop to the photosynthate sink in the parasite, as well as through the soil. We report the successful engineering of a mutant acetolactate synthase (ALS) gene into carrot, allowing control of broomrape already in heterozygotes of the first back-crossed generation, by imazapyr, an imidazolinone ALS inhibitor. It is expected that homozygotes will have higher levels of resistance.

Cell wall degrading enzymes in Orobanche aegyptiaca and its host Brassica campestris

Activities of the cell‐wall degrading enzymes cellulase (EC 3. 2. 1. 4). poly‐galacturonase (EC 3. 2. 1. 15) and xylanase (EC 3. 2. 1. 8), and also that of protease (EC 3. 4. 21. 14) have been determined in the parasite Orobanche aegyiptiaca Pers. and in the roots of infected and control host plants of Brassica campestris L. var. rapa Hartm. Shoots, roots and root‐freed tubers of Orobanche showed pronounced activities of these enzymes. When expressed in terms of specific activity, protease, cellulase and polygalacturonase activities were higher and xylanase lower in all parts of Orobanche than in the roots of infected or control host plants. Orobanche roots had higher activities of cellulase, polygalacturonase and protease than tuber or shoot. While xylanase activity was higher in the shoot than in roots or tuber. Infection by Orobanche significantly enhanced the cellulase activity of host roots. Cellulase and polygalacturonase in the Orobanche roots appear as the main enzymes involved in establishing haustorial connection with the host root. Protease might be involved in degrading proteins and lipoproteins of the cell walls and membranes of the host tissues.

Parasitic weeds and their impact in South-West Asia

SynopsisThree groups of SW Asiatic parasitic weeds are reviewed: the root parasites Striga (Scrophulariaceae), Cistanche and Orobanche (Orobanchaceae); and the stem parasites Cuscuta (Convolvulaceae). Striga hermonthka and S. asiatica are serious pests on sorghum, millet, and maize in parts of N and S Yemen and Saudi Arabia. Striga densiflora has apparently been introduced from India to Oman where it parasitises sugar-cane and sorghum. Species of Orobanche are widespread throughout almost all the region and cause serious losses in tomatoes, tobacco, broadbeans, melons and other crops. Cistanche phelypaea has recently been shown capable of attacking sugar beet. Species of Cuscuta (Convolvulaceae), widespread in SW Asia, mainly affect legume crops, especially lucerne. Considerable taxonomic research is still needed in Orobanche, Cistanche, and Cuscuta.

Glutamine Synthetase Isoenzymes ofStriga hermonthicaand other Angiosperm Root Parasites

The occurrence of multiple forms of glutamine synthetase in Striga hermonthica and other angiosperm root parasites was investigated. The facultative chlorophyllous parasite Melampyrum arvense exhibited two isoenzymes in leaf tissue, the cytosolic component (GS,) comprised less than 30% of total glutamine synthetase. In contrast GS, was the major component (<70%) in photosyntheti c tissue of Striga hermonthica and S. gesnerioides. Only a single isoenzyme (GS,) was detectable in the achlorophyllous root parasites Orobanche and Lathraea and in non-photosynt hetic tissue of 5. gesnerioides. The kinetic and physical properties of GS, and GS2 of these angiosperm parasites were similar to those of the isoenzymes in other non-parasitic angiosperms.

Quinolizidine Alkaloid Composition of Plants and of Photomixotrophic Cell Suspension Cultures ofSarothamnus scopariusandOrobanche rapum-genistae

The alkaloid composition of Sarothamnus scoparius cell cultures, plants and of its root parasite Orobanche rapum-genistae were analyzed by capillary gas-liquid chromatography (GLC) and capillary GLC/mass spectrometry. S. scoparius plants were found to contain the already known isosparteine, sparteine, 17-oxosparteine, lupanine and other quinolizidine alkaloids such as ammodendrine, N-methylangustifoline, alpha-isolupanine, 5,6-dehydrolupanine, 4-hydroxylupanine, 17-oxolupanine and five 13-hydroxylupanine esters. Two new alkaloids could be identified, a dehydrosparteine (presumably the 11,12-dehydroderivative) and a dihydroxylupanine (presumably 4,13-dihydroxylupanine). The distribution of these alkaloids within the different plant organs is reported. Orobanche rapum-genistae plants contain the already known sparteine, lupanine and 13-hydroxylupanine and 12 other lupin alkaloids, which are present in the Sarothamnus host plant. Photomixotrophic cell suspension cultures of S. scoparius accumulate lupanine as the main alkaloid. On tissue differentiation (bud formation) the cultures accumulate sparteine as well as lupanine. Whereas sparteine is stored in the cells, lupanine is excreted into the medium. Alkaloid formation of the cell cultures is positively correlated with chlorophyll content of the cells. The alkaloid pattern found in S. scoparius supports the hypothesis that lupanine biosynthesis is the common route of quinolizidine alkaloid biosynthesis from which the other alkaloids such as sparteine are derived.

Further Studies on the Effect of Various Crops on the Germination of Orobanche Seed

Abstract Twenty five crop plants were screened in pots to determine their reaction to the root parasite Orobanche cernua. Among them, tobacco, tomato and brinjal were found susceptible. Sunflower and safflower were found to act as false hosts, allowing the parasite to develop to pin-head sized infections on their roots. Chicory, niger, horsegram, linseed, lucerne, soyabean and chickpea were found to induce germination of Orobanche seed and received infections which died in the filamentous stage, thus behaving as effective trap crops. The remaining thirteen crop plants induced germination to a very limited extent.

Studies on the Physiology of Host‐parasite Relationship in Orobanche. I. Respiratory Metabolism of Host and Parasite

AbstractThe respiratory rate of the roots of mustard (Brassica cam‐pestris L.) and tomato (Lycopersicum esculentum Mill.) serving as hosts for the total root parasites Orobanche aegyptiaca Pers. and O.cernua Loefll. was measured using Warburg manometric technique. At the same time determinations were made of the respiration of the apical, basal and root regions of the parasites. The effects of sodium fluoride, malonic acid, sodium azide and DNP (2,4‐dinitrophenol) on the rate of respiration of the host roots as well as of the parasites were studied. The Orobanche infection results in a marked increase in the respiratory rate near the host‐parasite contact region. The damaging effect of infection seems to be due mainly to a continuous flow of water, minerals and metabolites from host to parasite. The haustorial invasion creates an obstruction in the translocation of metabolites. The respiration rate is lower in Orobanche than in the host, which might be related to its slower growth rate, inefficient oxidative processes and an escaping of certain energy‐requiring interconversion processes. Roots of O. aegyptiaca are more well‐developed and have higher rate of respiration. They can absorb more water and minerals from the soil. This fact might be connected with the specificity of the two species. NaF and malonic acid inhibit the respiration to a similar extent in healthy and infected roots. This indicates that the pathway of respiration does not change materially after infection. The EMP and Krebs cycle seem to operate at a lower intensity in Orobanche, which is proved by the lower inhibition of the respiration as compared to in the host. Azide causes a stronger reduction of the respiration in infected than in healthy roots. It would imply that the infection stimulates the activity of metal containing oxidases. The weaker inhibition of the respiration in Orobanche tissues indicates a mediation of other enzymes in the oxidation processes than in the host. The respiration is less stimulated by DNP in infected than in healthy roots. Contrary to the general effect of DNP, this substance decreases the O2 uptake in the parasite tissues. This fact may be explained by the occurrence of exceptionally high amounts of endogenous phenolic compounds and an insufficient production of ATP in the parasite.