La relation entre le Striga hermonthica et ses hôtes: une synthèse

1996 ◽  
Vol 74 (7) ◽  
pp. 1119-1137 ◽  
Author(s):  
Alain Olivier
Keyword(s):  
Control Method ◽  
Resistance Mechanisms ◽  
Striga Hermonthica ◽  
Effective Control ◽  
Parasitic Weed ◽  
New Methods ◽  
Interaction Control ◽  
Host Root ◽  
Germination Stimulants ◽  
Host Parasite

The parasitic weed Striga hermonthica causes considerable yield losses in maize, pearl millet, and sorghum in Africa. The extent of the damage caused to crops is related to their close interaction with the parasite. The S. hermonthica seed germinates in response to germination stimulants exuded by cereal roots. The rootlet extremity then turns into a haustorium that attaches itself to the host root and penetrates its tissue. In this manner, a connection is established between the vascular systems of both plants, allowing absorption of water, minerals, and organic compounds that are essential for the parasite's development. S. hermonthica also affects the host's metabolism and photosynthesis. No effective control method against the parasite is available for the African peasants. The utilization of germination stimulants and herbicides, the rotation practice, and intercropping as well as biological control and varietal selection have given disappointing results so far. A better understanding of host resistance mechanisms is necessary to develop new methods for the control of the parasite. Keywords: Striga hermonthica, germination, haustorium, host–parasite interaction, control methods, resistance.

scholarly journals Contrasting Response Mechanisms of Maize Lines to Striga hermonthica

Agriculture ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 485
Author(s):  
Nnanna N. Unachukwu ◽  
Abebe Menkir ◽  
Adekemi Stanley ◽  
Ebenezer O. Farombi ◽  
Melaku Gedil
Keyword(s):  
Cost Effective ◽  
Resistance Mechanisms ◽  
Control Measures ◽  
Sub Saharan Africa ◽  
Striga Hermonthica ◽  
Maize Line ◽  
Parasitic Weed ◽  
Resistant Lines ◽  
Sub Saharan ◽  
Better Than

Strigahermonthica (Del.) Benth is a parasitic weed that devastates cereals in Sub-Saharan Africa. Several control measures have been proposed for the parasite, of these, host plant resistance is considered the most cost-effective for poor farmers. Some tolerant/resistant lines have been developed and these lines display tolerance/resistance mechanisms to the parasite. A series of studies was done to investigate some of the mechanisms through which a resistant (TZISTR1108) and a susceptible (5057) maize line responds to S. hermonthica infestation, as well as the effects of parasitism on these lines. In this study, TZISTR1108 stimulated the germination and attachment of fewer S. hermonthica plants than 5057, both in the laboratory and on the field. In TZISTR1108, the growth of the S. hermonthica plants, that successfully attached, was slowed. When compared to the un-infested plants, the infested resistant plants showed fewer effects of parasitism than the infested susceptible plants. The infested TZISTR1108 plants were more vigorous, taller and resembled their un-infected counterparts. There were substantial reductions in the stomatal conductance and nitrogen content of the 5057 upon infestation. The resistant inbred line showed multiple mechanisms of resistance to S. hermonthica infestation. It thrives better than the susceptible line by reducing the attachment of S. hermonthica and it delays the parasite’s development.

Changes in the sensitivity of parasitic weed seeds to germination stimulants

2004 ◽  
Vol 14 (4) ◽  
pp. 335-344 ◽  
Author(s):  
Radoslava Matusova ◽  
Tom van Mourik ◽  
Harro J. Bouwmeester
Keyword(s):  
Rapid Change ◽  
Field Conditions ◽  
Striga Hermonthica ◽  
Wild Plant ◽  
Parasitic Weed ◽  
Germination Stimulant ◽  
Secondary Dormancy ◽  
Short Period ◽  
Weed Seeds ◽  
Germination Stimulants

The effects of preconditioning temperature and preconditioning period on the sensitivity of parasitic weed seeds to the synthetic germination stimulant GR24 were studied under laboratory and field conditions. The temperature during preconditioning ofOrobanche cumanaandStriga hermonthicaseeds strongly affected the responsiveness of the seeds to the applied germination stimulant. Preconditioning at an optimal temperature (21°C forO. cumanaand 30°C forS. hermonthica) rapidly released dormancy and increased the sensitivity to GR24 by several orders of magnitude. After reaching maximum sensitivity, prolonged preconditioning rapidly induced secondary dormancy, i.e. decreased sensitivity ofO. cumanaandS. hermonthicato GR24. The rapid change in sensitivity of preconditioned seeds to germination stimulants during prolonged preconditioning was particularly visible at low concentrations of GR24. GR24 at higher concentrations (0.1 and 1 mg l1) usually induced high germination of both species, regardless of the preconditioning period. The striking similarities between the response of parasitic weed seeds to GR24, described here, and results in the literature on non-parasitic wild plant seeds are discussed. Our results show that parasitic weed seeds are highly sensitive to the germination stimulant for a short period of time only, and then enter into secondary dormancy relatively quickly. The similar germination pattern ofS. hermonthicaseeds preconditioned for prolonged periods of time under laboratory and field conditions suggests that the mechanism observed is of ecological significance.

Physiology and histology of resistance to Striga hermonthica in Sorghum bicolor var. Framida

1999 ◽  
Vol 26 (1) ◽  
pp. 63 ◽  
Author(s):  
Marie-Claire Arnaud ◽  
Christophe Véronési ◽  
Patrick Thalouarn
Keyword(s):  
Growth Rate ◽  
Phenolic Compounds ◽  
Sorghum Bicolor ◽  
Resistance Mechanisms ◽  
Striga Hermonthica ◽  
Partial Inhibition ◽  
Development Of Resistance ◽  
Host Root ◽  
Sorghum Bicolor L

Germination, attachment to host root and growth of Striga hermonthica (Del.) Benth. seeds and seedlings were studied in in vitro co-culture w ith Sorghum bicolor (L.) Moench and in pot experiments. Two varieties, the resistant Framida and the susceptible CK-60B, were used. Histological, morphological and physiological studies revealed the key stages of resistance mechanisms involved. Resistance of Framida to Striga does not occur at the germination or the attachment stages, since its roots do not support fewer Striga than does CK-60B. As Framida roots support the lowest number of young Striga stems with scale leaves, its resistance appears to occur during the establishment of a functional haustorium. Metabolite uptake by the haustorium and growth rate of the young parasite were lower on Framida roots than on CK-60B roots, even when similarly developed haustoria were compared. Furthermore, at a later stage of infestation, significant accumulation of a coloured material likely to be rich in phenolic compounds was observed in and around Framida conductive tissues, but not CK-60B tissues. These features indicate the involvement of at least three steps in development of resistance in Framida roots: the first is linked to a partial inhibition of development of the young haustorium; the second could play a role in the physiological events that decrease nutrient translocation towards the haustoria; and the last seems to be associated with the accumulation of a coloured phenolic-like material.

scholarly journals A New Model Predictive Control Method for Eliminating Hydraulic Oscillation and Dynamic Hydraulic Imbalance in a Complex Chilled Water System

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3608
Author(s):  
Yang Yuan ◽  
Neng Zhu ◽  
Haizhu Zhou ◽  
Hai Wang
Keyword(s):  
Model Predictive Control ◽  
Predictive Control ◽  
Control Method ◽  
Water System ◽  
Energy Performance ◽  
Effective Control ◽  
New Model ◽  
Chilled Water ◽  
Chilled Water System ◽  
Hydraulic Oscillation

To enhance the energy performance of a central air-conditioning system, an effective control method for the chilled water system is always essential. However, it is a real challenge to distribute exact cooling energy to multiple terminal units in different floors via a complex chilled water network. To mitigate hydraulic imbalance in a complex chilled water system, many throttle valves and variable-speed pumps are installed, which are usually regulated by PID-based controllers. Due to the severe hydraulic coupling among the valves and pumps, the hydraulic oscillation phenomena often occur while using those feedback-based controllers. Based on a data-calibrated water distribution model which can accurately predict the hydraulic behaviors of a chilled water system, a new Model Predictive Control (MPC) method is proposed in this study. The proposed method is validated by a real-life chilled water system in a 22-floor hotel. By the proposed method, the valves and pumps can be regulated safely without any hydraulic oscillations. Simultaneously, the hydraulic imbalance among different floors is also eliminated, which can save 23.3% electricity consumption of the pumps.

scholarly journals Increased resilience for manufacturing systems in supply networks through data-based turbulence mitigation

2021 ◽  
Author(s):  
Dennis Bauer ◽  
Markus Böhm ◽  
Thomas Bauernhansl ◽  
Alexander Sauer
Keyword(s):  
Manufacturing Systems ◽  
Control Method ◽  
Great Influence ◽  
Learning System ◽  
Effective Control ◽  
Sufficient Information ◽  
Short Term ◽  
Data Format ◽  
Supply Networks ◽  
Manufacturing Control

AbstractIn manufacturing systems, a state of high resilience is always desirable. However, internal and external complexity has great influence on these systems. An approach is to increase manufacturing robustness and responsiveness—and thus resilience—by manufacturing control. In order to execute an effective control method, it is necessary to provide sufficient information of high value in terms of data format, quality and time of availability. Nowadays, raw data is available in large quantities. An obstacle to manufacturing control is the short-term handling of events induced by customers and suppliers. These events cause different kinds of turbulence in manufacturing systems. If such turbulences could be evaluated in advance, based on data processing, they could serve as aggregated input data for a control system. This paper presents an approach how to combine turbulence evaluation and the derivation of measures into a learning system for turbulence mitigation. Integrated in manufacturing control, turbulence mitigation increases manufacturing resilience and strengthens the supply network’s resilience.

scholarly journals Control Strategy Based on Arm-Level Control for Output and Circulating Current of MMC in Stationary Reference Frame

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4160
Author(s):  
Waqar Uddin ◽  
Tiago D. C. Busarello ◽  
Kamran Zeb ◽  
Muhammad Adil Khan ◽  
Anil Kumar Yedluri ◽  
...  
Keyword(s):  
Reference Frame ◽  
Control Method ◽  
Second Harmonic ◽  
Harmonic Component ◽  
Effective Control ◽  
Level Control ◽  
Circulating Current ◽  
Stationary Reference Frame ◽  
Pr Controller ◽  
Dc Component

This paper proposed a control method for output and circulating currents of modular multilevel converter (MMC). The output and circulating current are controlled with the help of arm currents, which contain DC, fundamental frequency, and double frequency components. The arm current is transformed into a stationary reference frame (SRF) to isolate the DC and AC components. The AC component is controlled with a conventional proportional resonant (PR) controller, while the DC component is controlled by a proportional controller. The effective control of the upper arm and lower arm ultimately controls the output current so that it delivers the required power to the grid and circulating current in such a way that the second harmonic component is completely vanished leaving behind only the DC component. Comparative results of leg-level control based on PR controller are included in the paper to show the effectiveness of the proposed control scheme. A three-phase, five-level MMC is developed in MATLAB/Simulink to verify the effectiveness of the proposed control method.

Mechanism and Effect of Nanoparticles on Controlling Fines Migration in Unconsolidated Sandstone Formations

SPE Journal ◽  
2021 ◽  
pp. 1-13
Author(s):  
Xin Zhao ◽  
Zhengsong Qiu ◽  
Jian Gao ◽  
Xiaoxia Ren ◽  
Jia Li ◽  
...  
Keyword(s):  
Interaction Energy ◽  
Control Method ◽  
Effective Control ◽  
Attractive Potential ◽  
Surface Element ◽  
Pore Surface ◽  
Microscopic Mechanism ◽  
Fines Migration ◽  
Favorable Conditions ◽  
Physical And Chemical

Summary Pore throat blockage due to fines migration during drilling and completion is one of the leading causes of damage to unconsolidated sandstone reservoirs. Therefore, it is necessary to explore an effective control method for fines migration. Five types of nanoparticles in suspension with aqueous NaCl solutions of six different ionic strengths were chosen. Their ability to control the migration of quartz and kaolinite fines in quartz sand as the porous medium is discussed in this work. Results show that nanoparticles can effectively adsorb and fix fines, thus successfully suppressing their migration. Among these nanoparticles, Al2O3 showed the best performance, and nanoparticle suspensions with higher ionic strengths were preferable. A surface element integration method was used to establish a mathematical model for calculating the interaction energy between the formation fines and the rock pore surface with adsorbed nanoparticles. Through atomic force microscopy and zeta potential measurements, the effect of nanoparticle adsorption on the heterogeneity of the pore surface was analyzed in terms of roughness and electrical properties. The interaction energy between the formation fines and the heterogeneous pore surface was calculated; it revealed the microscopic mechanism of how nanoparticles control fines migration. The results indicated that the nanoparticles form an adsorption layer, which enhances the physical and chemical heterogeneities of the pore surface and provides favorable conditions for the adsorption and fixation of fines. As a result, the interaction energy curves of the fines and the pore surface shift downward, and their repulsive barriers decrease or even disappear, exhibiting higher attractive potential energy. These variations promote adsorption and fixation of fines at the pore surface, as confirmed by the experimental results reported in this work, thus successfully preventing formation damage.

An experimental evaluation of conventional control measures against the sheep tick, Ixodes ricinus (L.) (Acari: Ixodidae). II. The dynamics of the tick-host interaction

1985 ◽  
Vol 75 (3) ◽  
pp. 501-518 ◽  
Author(s):  
Sarah E. Randolph ◽  
Gordon M. Steele
Keyword(s):  
Ixodes Ricinus ◽  
Control Method ◽  
Control Strategies ◽  
Stocking Density ◽  
Experimental Manipulation ◽  
Control Measures ◽  
Effective Control ◽  
Contact Rate ◽  
Host Interaction ◽  
Questing Ticks

AbstractThe experimental manipulation of separate, but originally identical, populations of Ixodes ricinus (L.) by applying three conventional tick control measures in different enclosures on naturally infested moorland in Wales allowed the elements of the tick-host interaction to be analysed quantitatively and the effectiveness of the control methods to be compared. From the relationship between the sheep stocking density and the numbers of questing ticks picked up by fortnightly blanket-dragging in each enclosure, the death rate of ticks during their activity season and the rate of contact between sheep and ticks were calculated. From this, it was possible to investigate the effect of different stocking densities on the feeding success of ticks. A major factor determining the much lower contact rate for larvae than for nymphs was the different spatial distribution of questing ticks, clumped for larvae and random for nymphs. The non-random use by sheep of the three different vegetation zones in the paddock resulted in the highest contact rate between sheep and ticks in the pasture area, but tick survival was apparently highest in the bog area. Combining these factors resulted in the prediction that the bracken area was the least favourable habitat for ticks. In the two enclosures where the sheep were not treated with acaricide the mean tick loads on the sheep were similar, but the lower overall use of the pasture by the sheep in the low stocking density enclosure (2/ha) resulted in slightly lower tick loads there compared with those in the high stocking density enclosure (4/ha). The numbers of ticks counted in the second year showed that pasture spelling was the most effective control method, acaricide treatment was less effective, and the benefits of halving the stocking density were marginal. The implications of these results for control strategies are discussed.

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