Amar Matloob

Phytohormones and plant responses to salinity stress: a review

Plants are exposed to a variety of abiotic stresses in nature and exhibit unique and complex responses to these stresses depending on their degree of plasticity involving many morphological, cellular, anatomical, and physiological changes. Phytohormones are known to play vital roles in the ability of plants to acclimatize to varying environments, by mediating growth, development, source/sink transitions and nutrient allocation. These signal molecules are produced within the plant, and also referred as plant growth regulators. Although plant response to salinity depends on several factors; nevertheless, phytohormones are thought to be the most important endogenous substances that are critical in modulating physiological responses that eventually lead to adaptation to salinity. Response usually involves fluctuations in the levels of several phytohormones, which relates with changes in expression of genes involved in their biosynthesis and the responses they regulate. Present review described the potential role of different phytohormones and their balances against salinity stress and summarized the research progress regarding plant responses towards salinity at physiological and molecular levels. We emphasized the role of abscisic acid, indole acetic acid, cytokinins, gibberellic acid, salicylic acid, brassinosteroids, jasmonates, ethylene and triazoles in mediating plant responses and discussed their crosstalk at various baseline pathways transduced by these phytohormones under salinity. Current progress is exemplified by the identification and validation of several significant genes that enhanced crops tolerance to salinity, while missing links on different aspects of phytohormone related salinity tolerance are pointed out. Deciphering mechanisms by which plant perceives salinity and trigger the signal transduction cascades via phytohormones is vital to devise salinity related breeding and transgenic approaches.

Phytoremediation strategies for soils contaminated with heavy metals: Modifications and future perspectives

Presence of heavy metals in agricultural soils is of major environmental concern and a great threat to life on the earth. A number of human health risks are associated with heavy metals regarding their entry into food chain. Various physical, chemical and biological techniques are being used to remove heavy metals and metalloids from soils. Among them, phytoremediation is a good strategy to harvest heavy metals from soils and have been proven as an effective and economical technique. In present review, we discussed various sources and harmful effects of some important heavy metals and metalloids, traditional phytoremediation strategies, mechanisms involved in phytoremediation of these metals, limitations and some recent advances in phytoremediation approaches. Since traditional phytoremediation approach poses some limitations regarding their applications at large scale, so there is a dire need to modify this strategy using modern chemical, biological and genetic engineering tools. In view of above, the present manuscript brings both traditional and advanced phytoremediation techniques together in order to compare, understand and apply these strategies effectively to exclude heavy metals from soil keeping in view the economics and effectiveness of phytoremediation strategies.

Effect of crop residues applied isolated or in combination on the germination and seedling growth of horse purslane (Trianthema portulacastrum)

Soil incorporation of crop residues can lead to weed suppression by posing allelopathic and physical effects. Allelopathic potential of the crops sorghum, sunflower, brassica applied as sole or in combination for horse purslane (Trianthema portulacastrum) suppression was evaluated in a pot investigation. Chopped crop residues alone and in combination were incorporated at 6 g kg-1 soil (12 t ha-1), and a weedy check was maintained. Germination traits time to start germination; time to 50% emergence, mean emergence time, emergence index and final germination percentage were negatively influenced by residue incorporation. Crop residues also exerted a pronounced negative influence on the shoot and root length of horse purslane. Significant suppression in leaf and root score and leaf area per plant was also observed. A combination of sorghum and sunflower residues accounted for maximum (71%) seedling mortality. Soil incorporation of allelopathic crop residues can be employed for horse purslane management.

Reduced Doses of a Sulfonylurea Herbicide for Weed Management in Wheat Fields of Punjab, Pakistan

Reduction in herbicide usage without compromising yields can lead to less environmental harm and lower production costs. Field trials were conducted to appraise the efficacy of reduced doses (25, 50, and 75% of the label dose) of a post emergence sulfonylurea herbicide [Atlantis 3.6WG (iodo+mesosulfuron)] to control weeds in wheat (Triticum aestivum L.) fields of Punjab, Pakistan. Below-labeled-doses were quite effective in suppressing total weed density (72-95%) and biomass (8394%), and wheat grain yield was increased by 22 to 48% over the weedy control, while label dose of iodo+mesosulfuron improved yield by 53%. Iodo+mesosulfuron at 25 and 50% of the label dose inhibited grass weeds by 43 to 64%, albeit their biomass was suppressed by > 80% over control. Wheat yields for reduced herbicide doses (50 and 75%) were not different with label dose. Economic analysis revealed that the maximum marginal rate of return was recorded for 50% of the label herbicide dose and was followed by that observed for 25% of the label dose. Reduced doses of herbicide can be an effective tool in minimizing herbicide inputs and lowering production costs in wheat production without compromising yields.

Allelopathic Activity of Crop Residue Incorporation Alone or Mixed Against Rice and its Associated Grass Weed Jungle Rice (Echinochloa colona [L.] Link)

La represion de malezas es uno de los beneficios logrados por la incorporacion de residuos de cosecha al suelo y se cree que es de naturaleza alelopatica. Se evaluo el potencial alelopatico de diversos residuos de cultivos: sorgo (Sorghum bicolor [L.] Moench), girasol (Helianthus annuus L.) y coles (Brassica Compestris L.) en arroz (Oryza sativa L.) y pasto arroz o pasto Shama (Echinochloa colona [L.] Link). Los residuos de cosecha picados se incorporaron solos y en mezcla a 6 g kg-1 de suelo (12 t ha-1) y se compararon con un testigo sin residuos. La incorporacion de los residuos al suelo retraso sustancialmente la germinacion del pasto arroz o pasto Shama. El tiempo para empezar la germinacion, el tiempo a 50% de emergencia, el tiempo medio de emergencia, el indice de emergencia, y el porcentaje de germinacion final fueron influidos negativamente por la incorporacion de residuos. La germinacion final del arroz y del pasto arroz o pasto Shama se redujo en 11 a 15% y 11 a 27% con el uso exclusivo de residuos, y en 18 a 22% y 8 a 34% con la combinacion de los residuos de cultivos, respectivamente. Los residuos de cultivos ejercieron una marcada influencia negativa en la longitud de brotes (25-100% y 14-44%) y la longitud de raices (22-100% y 10-43%) de arroz y de pasto arroz o pasto Shama, respectivamente. Peso seco de brotes y raices de arroz y pasto del arroz o pasto Shama tambien decrecieron significativamente. Una apreciable cantidad de fenoles fue registrada en el suelo enmendado con residuos de sorgo+girasol+coles. Desde que los residuos alelopaticos de cultivos se incorporaron al suelo tambien fueron perjudiciales para la germinacion y crecimiento de las plantulas de arroz, asi se sugiere que el momento de la aplicacion de los residuos para la supresion de arroz de la selva y el tiempo de la siembra del arroz deben ser ajustados para reducir al minimo el dano del cultivo de arroz.

Weeds in a changing climate: vulnerabilities, consequences, and implications for future weed management

Whilst it is agreed that climate change will impact on the long-term interactions between crops and weeds, the results of this impact are far from clear. We suggest that a thorough understanding of weed dominance and weed interactions, depending on crop and weed ecosystems and crop sequences in the ecosystem, will be the key determining factor for successful weed management. Indeed, we claim that recent changes observed throughout the world within the weed spectrum in different cropping systems which were ostensibly related to climate change, warrant a deeper examination of weed vulnerabilities before a full understanding is reached. For example, the uncontrolled establishment of weeds in crops leads to a mixed population, in terms of C3 and C4 pathways, and this poses a considerable level of complexity for weed management. There is a need to include all possible combinations of crops and weeds while studying the impact of climate change on crop-weed competitive interactions, since, from a weed management perspective, C4 weeds would flourish in the increased temperature scenario and pose serious yield penalties. This is particularly alarming as a majority of the most competitive weeds are C4 plants. Although CO2 is considered as a main contributing factor for climate change, a few Australian studies have also predicted differing responses of weed species due to shifts in rainfall patterns. Reduced water availability, due to recurrent and unforeseen droughts, would alter the competitive balance between crops and some weed species, intensifying the crop-weed competition pressure. Although it is recognized that the weed pressure associated with climate change is a significant threat to crop production, either through increased temperatures, rainfall shift, and elevated CO2 levels, the current knowledge of this effect is very sparse. A few models that have attempted to predict these interactions are discussed in this paper, since these models could play an integral role in developing future management programs for future weed threats. This review has presented a comprehensive discussion of the recent research in this area, and has identified key deficiencies which need further research in crop-weed eco-systems to formulate suitable control measures before the real impacts of climate change set in.

Weed Management in Dry-Seeded Fine Rice under Varying Row Spacing in the Rice-Wheat System of Punjab, Pakistan

Abstract Direct seeding can curtail water and labor inputs involved in rice production; nevertheless, its large-scale adoption is impeded by heavy weed infestation. A field study was undertaken in 2011 and 2012 to evaluate the effects of crop row spacing (20 and 10 cm) and postemergence herbicides on weed growth and yield of dry-seeded rice. As a herbicide, pyrazosulfuron ethyl at 30 g ha–1, bispyribac-sodium at 30 g ha–1, or penoxsulam at 15 g ha–1 was applied (15 days after sowing, DAS) alone or in combination with fenoxaprop-p-ethyl at 86.25 g ha–1 subsequently (30 DAS). In addition, a partial weedy plot (manually weeded once at 28 DAS), and a weed-free plot were established for each row spacing In the partial weedy plot with 10-cm row spacing, the weed density was only 21 and 25% lower than that in the plot with 20-cm row spacing in 2011 and 2012, respectively. The sole application of an early postemergence herbicide restricted weed growth, while subsequent application of fenoxaprop as late postemergence application suppressed weed growth further, the magnitude of suppression being more pronounced in the plot with narrow row spacing. The density and biomass of weeds were lowest in the plot with 10-cm row spacing applied bispyribac-sodium followed by fenoxaprop . Under weed-free conditions, yields were 29% higher in the plot with 10-cm row spacing (4.18 t ha–1) than in that with 20-cm row spacing (3.23 t ha–1). Grain yield in the herbicide-treated plots was 87 – 188% higher than that in the partial weedy plots. These results suggested that narrow row spacing and sequential herbicide application can help tackle recalcitrant weed flora in dry-seeded rice fields.

Allelopathic effects of aqueous and organic fractions of Euphorbia dracunculoides Lam. on germination and seedling growth of chickpea and wheat

Se requiere la identificacion de especies de malezas con potencial alelopatico y la caracterizacion de sus efectos adversos en contra de los cultivos asociados para una mejor comprension de las interacciones cultivos-malezas. Se investigo la actividad fitotoxica de Euphorbia dracunculoides Lam. en la germinacion y crecimiento de plantulas de garbanzo (Cicer arietinum L.) y trigo (Triticum aestivum L.) bajo condiciones controladas. Dos estudios separados se realizaron con cada una de las cuatro fracciones de disolventes organicos (n-hexano, cloroformo, acetato de etilo, 1-butanol) y extracto acuoso (1:10 y 1:20) de fracciones enteras de plantas de E. dracunculoides usando agua destilada y 0,05% (v/v) dimetil sulfoxido (DMSO) como control. Diferentes fracciones acuosas y organicas de E. dracunculoides tuvieron una incidencia significativa en los atributos de germinacion y crecimiento de las plantulas de las especies evaluadas. El porcentaje de germinacion final de trigo no se vio afectado, sin embargo, la elongacion de raices y brotes y la acumulacion de biomasa en estas partes fueron significativamente retrasadas. La fraccion acuosa fue mas itotoxica que las fracciones organicas y disminuyo la germinacion de garbanzo en 53% y 35% para 1:10 y 1:20, respectivamente. Estas fracciones acuosas, 1:10 y 1:20, tambien redujeron la longitud de raices (75-64% y 33-34%) y brotes (62-18% y 21-21%) y el peso seco de raices (32-33% y 42-46%) y brotes (32-7% y 8480%) para trigo y garbanzo, respectivamente. Entre las fracciones organicas, n-hexano fue la mas supresora de las especies ensayadas. El analisis cromatograico detecto la presencia de cuatro itotoxinas en la fraccion acuosa (1:10) de la planta: acido furoico, acido p-cumarico, acido cafeico, y acido siringico. El estudio determino que E. dracunculoides es alelopatica sobre el trigo y el garbanzo.

Differential suppression of rice weeds by allelopathic plant aqueous extracts

Herbicidal potential of different plant aqueous extracts was evaluated against early seedling growth of rice weeds in pot studies. Plant aqueous extracts of sorghum (Sorghum bicolor), sunflower (Helianthus annuus), brassica (Brassica compestris), mulberry (Morris alba), eucalyptus (Eucalyptus camaldunensis), and winter cherry (Withania somnifera) at a spray volume of 18 L ha-1 each at the 2-4 leaf stage of rice weeds viz horse purslane (Trianthema portulacastrum) [broad-leaf], jungle rice (Echinochloa colona), and E. crus-galli (barnyard grass) [grasses] and purple nut sedge (Cyperus rotundus) and rice flat sedge (C. iria) [sedges]. The results showed significant interactive effects between plant aqueous extracts and the tested weed species for seedling growth attributes depicting that allelopathic inhibition was species-specific. Shoot and root length, lateral plant spread, biomass accumulation, and leaf chlorophyll contents in test species were all reduced by different extracts. The study suggested the suppressive potential of allelopathic plant aqueous extracts against rice weeds, and offered promise for their usefulness as a tool for weed management under field conditions.

Toxic action of aqueous wheat straw extract on horse e purslane

The toxic action of aqueous wheat (Triticum aestivum) straw extracts was investigated on germination, early seedling growth, some biochemical attributes and the antioxidant enzymes of horse purslane (Trianthemaportulacastrum). Aqueous extracts of wheat straw were prepared by soaking the wheat straw in distilled water in 1:10 w/v ratio and diluted to obtain the concentrations of 0, 25, 50, 75 and 100%. These were used as pre and post emergence in laboratory and screen house trials. Wheat aqueous extracts exhibited phytotoxicity to horse purslane by inhibiting and delaying its germination and suppressing seedling growth. Wheat phytotoxins in its aqueous extracts suppressed the chlorophyll content and soluble protein, and enhanced soluble phenolics and the activity of antioxidant enzymes as catalase, peroxidase and superoxide dismutase in the seedlings of horse purslane compared with the control. Such inhibitory activity is believed to originate from exposure to wheat phytotoxins that are present in its aqueous straw extract. The suppressive effects of wheat straw need to be investigated further under field conditions.