Jamal R. Qasem

Bio: Jamal R. Qasem is an academic researcher from University of Jordan. The author has contributed to research in topics: Weed & Allelopathy. The author has an hindex of 20, co-authored 80 publications receiving 1313 citations. Previous affiliations of Jamal R. Qasem include University of London.

Weed allelopathy, its ecological impacts and future prospects: a review

Abstract: Summary The importance, characteristics, positive and negative impacts, and future role of weeds as an integral part of the natural and agroecosystems are evaluated and discussed. Interference between plants in nature and the importance of differentiating between competition and allelopathy are interpreted. Allelopathy as one component of weed/crop interference, allelochemicals from weed species and their possible mechanism of action are listed and discussed. Weed species with inhibitory action against cultivated crops, other weed species, and plant pathogens, as well as self-inhibitory (autopathic) species are reviewed. Stimulatory or inhibitory allelopathic effects of different crop plants, trapping and catching species, and the potential of allelopathic weeds in inhibiting or stimulating certain parasitic weed species are discussed and evaluated. Allelopathy as a mechanism and future strategy for agricultural pest control and farm management and the potential use and development of some allelochemicals...

Fungicidal Activity of Some Common Weed Extracts Against Different Plant Pathogenic Fungi

Abstract: Aqueous extract effects of 64 weed species on growth and development of Alternaria solani Sorauer, Helminthosporium sativum King & Bakke and Rhizoctonia solani Kuhn, plant pathogenic fungi were studied in vitro. Extracts varied in the strength and persistence of their antifungal effects against the three fungi species. Some stimulated, others inhibited or had no effect. Among all species tested, extracts of Chenopodium murale, Falcaria vulgaris, Ranunculus asiaticus and Sisymbrium irio were the most toxic to A. solani. Anagallis arvensis, Atriplex leucoclada, Crepis aspera, Notobasis syriaca, R. asiaticus, Rumex crispus, S. irio, Sonchus oleraceous and Vicia narbonensis to H.sativum and R. asiaticus, S. oleraceous and Mercurialis annua to R. solani. However, R. asiaticus extract was the most effective and completely inhibited growth and sporulation of the three fungi species at all incubation periods.

Nutrient accumulation by weeds and their associated vegetable crops

Abstract: A field study showed that weeds are better nutrient accumulators than tomato and bean crops. Percentages of N, P, K, and Mg in shoots of most weed species were higher than in crop plants. Weeds associated with bean accumulated more P in roots than did crop plants, and weeds of tomato field contained higher percentages of P and K than the crop. All weed species showed lower concentration of Ca in shoots and roots than did crop plants. Weeds varied substantially in their shoot and root percentages of mineral elements and differences in nutrient percentages between shoots and roots of weeds were greater than with crop plants. Malvasylvestris, Chenopodium murale, Portulaca oleracea and Rumex obtusifolius are nutrient accumulator weeds. Tomato appeared to be better than bean in competition with weeds.

The allelopathic effect of three Amaranthus spp. (pigweeds) on wheat (Triticum durum)

Abstract: Summary The allelopathic effect of Amaranthus retroflexus L., Amaranthus blitoides S. Wats, and Amaranthus gracilis Desf. on wheat Triticum durum L. was investigated under laboratory, glasshouse and field conditions. Laboratory experiments showed that fresh shoot or root extract of the three weed species reduced germination, coleoptile length, root length and root dry weight of wheat seedlings. The inhibitory effects were rate dependent, with low concentrations of shoot extract promoting shoot growth of wheat. Fresh plant extracts were more phytotoxic than dried plant extracts and shoot extracts had higher detrimental effects than root extracts. In pot experiments, dried shoot extract of A. gracilis increased shoot and root dry weights of wheat seedlings. For A retroflexus and A. blitoides the extracts of these and dried shoots (8 g kg−1), which had been added to soil mixtures significantly reduced ger-mination and growth of wheat seedlings. Addition of up to 16 g kg−1 of A. gracilis residues promoted shoot growth of wheat and had no significant harmful effect on root growth. Roots appeared more sensitive to allelopathic effect than shoots. Under field conditions, incorporation of A. retroflexus or A. blitoides residues in the soil reduced height, grain and straw yield of wheat, whereas A. gracilis residues stimulated plant height and increased yield.

On difficulties with allelopathy methodology

Abstract: Summary. The main techniques and the common experimental methods used in studying allelopathy are reviewed. Problems associated with both methodology and conclusions drawn based on certain techniques are discussed. The accuracy obtained using these techniques is evaluated and show that some of the techniques could be a misleading tool. Some changes are suggested. Resume. Des difficultes de la methodologie en matiere d'allelopathie Les principales techniques et les methodes experi-mentales usuelles utilisees pour etudier l'alleopathie sont passees en revue. Les problemes lies tant a la methodologie qu'aux conclusions tirees a partir de certaines techniques sont discutes. La precision obtenue par ces techniques est evaluee. Certaines de ces techniques discutees pourraient etre un outil trompeur pour les recherches en allelopathie. Quelques changements utiles sont suggeres. Zusammenfassung. Problematik der Untersuchung allelopathischer Wirkungen Die gebrauchlichen Techniken und Methoden zur Untersuchung allelopathischer Wirkungen wurden referiert und die Probleme, die sowohl mit der Methodik als auch mit den Schlusfolgerungen aus mit bestimmten Methoden gewonnenen Ergebnissen verbunden sind, wurden erortert. Die Genauigkeit der Ergebnisse aus Versuchen mit diesen Methoden wurde untersucht. Einige Methoden scheinen fur die Untersuchunt allelopathischer Wirkungen ungeeignet zu sein, und es wurden Verbesserungen vorgeschlagen.

Understanding options for agricultural production.

Abstract: Preface. Acronyms. 1. Overview of IBSNAT G. Uehara, G.Y. Tsuji. 2. Data for Model Operation, Calibration, and Evaluation L.A. Hunt, K.J. Boote. 3. Soil Water Balance and Plant Water Stress J.T. Ritchie. 4. Nitrogen Balance and Crop Response to Nitrogen in Upland and Lowland Cropping Systems D.C. Godwin, U. Singh. 5. Cereal Growth, Development and Yield J.T. Ritchie, et al. 6. The CROPGRO Model for Grain Legumes K.J. Boote, et al. 7. Modeling Growth and Development of Root and Tuber Crops U. Singh, et al. 8. Decision Support System for Agrotechnology Transfer: DSSAT v3 J.W. Jones, et al. 9. Modeling and Crop Improvement J.W. White. 10. Simulation as a Tool for Improving Nitrogen Management W.T. Bowen, W.E. Baethgen. 11. The Use of a Crop Simulation Model for Planning Wheat Irrigation in Zimbabwe J.F. MacRobert, M.J. Savage. 12. Simulation of Pest Effects on Crops Using Coupled Pest-Crop Models: The Potential for Decision Support P.S. Teng, et al. 13. The Use of Crop Models for International Climate Change Impact Assessment C. Rosenzweig, A. Iglesias. 14. Evaluation of Land Resources Using Crop Models and a GIS F.H. Beinroth, et al. 15. The Simulation of Cropping Sequences Using DSSAT W.T. Bowen, et al. 16. Risk Assessment and Food Security P.K. Thornton, P.W. Wilkens. 17. Incorporating Farm Household Decision-Making within Whole Farm Models G. Edwards-Jones, et al. 18. Network Management and Information Dissemination for Agrotechnology Transfer G.Y. Tsuji. 19. Crop Simulation Models as an Educational Tool R.A. Ortiz. 20. Synthesis G. Uehara.

Allelopathic Interactions and Allelochemicals: New Possibilities for Sustainable Weed Management

Abstract: Weeds are known to cause enormous losses due to their interference in agroecosystems. Because of environmental and human health concerns, worldwide efforts are being made to reduce the heavy reliance on synthetic herbicides that are used to control weeds. In this regard the phenomenon of allelopathy, which is expressed through the release of chemicals by a plant, has been suggested to be one of the possible alternatives for achieving sustainable weed management. The use of allelopathy for controlling weeds could be either through directly utilizing natural allelopathic interactions, particularly of crop plants, or by using allelochemicals as natural herbicides. In the former case, a number of crop plants with allelopathic potential can be used as cover, smother, and green manure crops for managing weeds by making desired manipulations in the cultural practices and cropping patterns. These can be suitably rotated or intercropped with main crops to manage the target weeds (including parasitic ones) selectively. Even the crop mulch/residues can also give desirable benefits. Not only the terrestrial weeds, even allelopathy can be suitably manipulated for the management of aquatic weeds. The allelochemicals present in the higher plants as well as in the microbes can be directly used for weed management on the pattern of herbicides. Their bioefficacy can be enhanced by structural changes or the synthesis of chemical analogues based on them. Further, in order to enhance the potential of allelopathic crops, several improvements can be made with the use of biotechnology or genomics and proteomics. In this context either the production of allelochemicals can be enhanced or the transgenics with foreign genes encoding for a particular weed-suppressing allelochemical could be produced. In the former, both conventional breeding and molecular genetical techniques are useful. However, with conventional breeding being slow and difficult, more emphasis is laid on the use of modern techniques such as molecular markers and the selection aided by them. Although the progress in this regard is slow, nevertheless some promising results are coming and more are expected in future. This review attempts to discuss all these aspects of allelopathy for the sustainable management of weeds.

Weed management in organic agriculture: are we addressing the right issues?

Abstract: Summary Despite the serious threat which weeds offer to organic crop production, relatively little attention has so far been paid to research on weed management in organic agriculture, an issue that is often approached from a reductionist perspective. This paper aims to outline why and how this problem should instead be tackled from a system perspective. Compared with conventional agriculture, in organic agriculture the effects of cultural practices (e.g. fertilization and direct weed control) on crop:weed interactions usually manifest themselves more slowly. It follows that weed management should be tackled in an extended time domain and needs deep integration with the other cultural practices, aiming to optimize the whole cropping system rather than weed control per se. In this respect, cover crop management is an important issue because of its implications for soil, nutrient, pest and weed management. It is stressed that direct (physical) weed control can only be successful where preventive and cultural weed management is applied to reduce weed emergence (e.g. through appropriate choice of crop sequence, tillage, smother/cover crops) and improve crop competitive ability (e.g. through appropriate choice of crop genotype, sowing/planting pattern and fertilization strategy). Two examples of system-oriented weed management systems designed for organic agriculture are illustrated as well as future perspectives and problems.

Weed and Crop Allelopathy

Abstract: Allelopathy can be defined as an important mechanism of plant interference mediated by the addition of plant-produced secondary products to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization, and root exudation. Allelochemical structures and modes of action are diverse and may offer potential for the development of future herbicides. We have focused our review on a variety of weed and crop species that establish some form of potent allelopathic interference, either with other crops or weeds, in agricultural settings, in the managed landscape, or in naturalized settings. Recent research suggests that allelopathic properties can render one species more invasive to native species and thus potentially detrimental to both agricultural and naturalized settings. In contrast, allelopathic crops offer strong potential for the development of cultivars that are ...