Reza Ghorbani

Evaluation of Alternaria alternata for biological control of Amaranthus retroflexus

Abstract Amaranthus retroflexus L. is a common annual weed worldwide. It can be found in a wide range of habitats and causes substantial yield reduction in many crops mainly through competition. Alternaria spp. are airborne molds that are considered to have potential for the biological control of weeds. The aim of this study was to assess the effect of spore concentration, host-plant growth stage, dew period, and temperature on the pathogenicity of three Alternaria alternata isolates against A. retroflexus. The pathogenicity of A. alternata increased with increasing spore concentration and length of dew period. A spore concentration of 107 spores ml−1 in a rapeseed oil emulsion and given a 24 h dew period caused 100% mortality of A. retroflexus plants at the four-leaf stage. Infection and mortality in older plants (>four-leaf stage) was lower. The highest levels of plant mortality were obtained at post-inoculum temperatures between 20 and 30 C. These experiments confirm the potential of A. alternata as a mycoherbicide under specific environmental conditions. Nomenclature: Alternaria alternata L.; Amaranthus retroflexus L. AMARE, redroot pigweed.

Effect of cropping systems and crop rotations on weeds

Dynamics of weed populations in arable fields are influenced by environmental and soil characteristics and also by cropping system and management practices. Manipulation of cropping systems to improve weed management requires a better understanding of the spatial and temporal dynamics of weeds, seed losses and seed production. To assess the effect of different cropping systems and various crop rotations on the weed population and seed bank, we conducted a field study at the experimental farm in Khorasan Agricultural Research Center, Mashhad, Iran. The experimental design was a split plot with 3 crop rotations as the main plots, and five cropping systems consisting of high-input, medium-input, low-input, organic and integrated systems applied to the sub-plots. Our results show that weed seed densities in organic and integrated cropping systems, of about 5000–6000 seeds/m2 were higher than conventional and high-input cropping systems showing about 2000 seeds/m2. Weed seed density in continuous winter wheat of approximately 6300 seeds/m2 was higher than other rotations with about 5000 seeds/m2. Weed composition in the high-input system was 11 species with 66 plants/m2. Whereas in the low-input and organic systems, the weed populations were 15 and 13 species with 145 and 220 plants/m2, respectively. Changes in weed seed bank density and species composition often occur when crop management practices and crop rotations are altered. For example, continuous winter wheat fields showed more annual grass weeds, but broadleaf weeds were more abundant in sugar beet-winter wheat rotation. The weed population in continuous winter wheat plots comprised 90% grass and sedge weeds, while in sugar beet-wheat rotation, it was only 43% of total weed density. Broadleaf weeds were 55.2% in sugar beet-winter wheat but 9.4% of total weed density in continuous winter wheat. Different rotations that include crops with different life cycles such as winter wheat-maize and winter wheat-sugar beet could lead to additional benefits of reducing the weed seed bank.

Improvement of late blight management in organic potato production systems in Europe: field tests with more resistant potato varieties and copper based fungicides

ABSTRACT Late blight of potatoes, caused by Phytophthora infestans, is particularly difficult to prevent or control in organic agriculture. In this study, the host resistance of selected varieties to foliar and tuber blight and their yield under organic growing conditions were assessed in trials carried out in four countries (Switzerland, France, England and Norway) in 2001 and 2002. The objective was to identify new, more resistant varieties, which might replace some of the more susceptible varieties which are currently grown in organic agriculture. In each country, five test varieties were compared with two reference varieties, identical for all sites, and with two locally popular varieties. In addition, the effect of copper fungicides was assessed for all varieties in England. Several new potato varieties (Appell, Derby, Innovator and Naturella in Switzerland; Derby, Eden, Escort and Naturella in France; Sarpo Axona, Eve Balfour, Lady Balfour, Sarpo Mira and Sarpo Tominia in England; N89-1756 and N92-15138 in Norway) proved for less susceptible to foliar and tuber blight than most of the varieties currently grown. However, market requirement could restrict their introduction in to practice. The copper fungicide treatment reduced foliar blight severity in all varieties tested in England and in both years, by 27% on average, and increased yield by 20% on average, but did not affect tuber blight. In organic farming, a shift towards the use of blight resistant varieties should thus be strongly encouraged, although this is unlikely to eliminate the need to use copper fungicides.

Alternative treatments for late blight control in organic potato: Antagonistic micro-organisms and compost extracts for activity against Phytophthora infestans.

SummaryThe effects of various fungi, bacteria and different compost extracts on foliar infection of potato (Solatium tuberosum) withPhytophthora infestans were tested in detached leaf bioassays in 2001–2003. Application of microorganism inocula and compost extracts as well as copper oxychloride to excised leaves resulted in different degrees of blight control. In general, suppression of blight lesion growth was not improved by applying the antagonists before the leaves were inoculated withPhytophthora spores. There was some evidence that extracts made from different compost feed stocks of different ages suppressed leaflet infection with blight. However, results were very limited and inconsistent. Moreover, the effects were much smaller than where copper oxychloride was used. Improved efficacy of acceptable alternatives to copper fungicides especially in organic farming is required. No promising effective alternative to the use of copper fungicides to reduce late blight infection in organic potato production systems was identified in the experiments.

Impact of organic amendments and compost extracts on tomato production and storability in agroecological systems

The sustainability of a farm system greatly relies on fertilizers and other inputs. Soil factors such as texture and local rainfall, along with management-related factors such as soil organic matter, aggregate stability and agronomic practices, have much greater influence on the sustainability of any given farm than do the type or amount of soil amendments. Growers use a wide variety of practices to maintain or improve soil health in organic vegetable production systems. These practices generally are part of long-term, site-specific management programs that aim at developing fertile and biologically active soils that readily capture and store water and nutrients, have good tilth, and suppress plant diseases. Field experiments were conducted in 2005 and 2006 in Mashhad, Iran, to study the effects of organic amendments, synthetic fertilizers and compost extracts on crop health, productivity and storability of tomato (Lycopersicon esculentum Mill.). Treatments included different fertilizers of cattle, sheep and poultry manures, green-waste and household composts and chemical fertilizers of urea and superphosphate; and five aqueous extracts from cattle manure, poultry manures, green-waste, and household composts plus water as control. Our results show that application of poultry manure showed lower disease incidence, as shown by 80% healthy tomato, compared with the other fertilizers. However, the organic fertilizers used did not give higher yields compared with chemical fertilizers. Sheep manure and chemical fertilizers led to the highest total tomato yield. Marketable yield was highest in poultry manures, of 16 t/ha, and lowest in chemical fertilizer, of 7 t/ha, 6 weeks after storage. The effect of aqueous extracts was not significant on either crop health or tomato yield and the results were inconsistent. The compost made of poultry manure therefore appears to be a promising ecological alternative to classical fertilizers.

Effects of Presprouting, Planting Date, Plant Population and Configuration on Late Blight and Yield of Organic Potato Crops Grown with Different Cultivars

In organic systems of agriculture, integrated control strategies are necessary for the management of late blight. Agronomic treatments such as presprouting of seed tubers, planting early and in different populations and spacings should be considered for inclusion. They may delay and/or decrease infection and help to ensure that acceptable marketable yields are achieved before the disease prevails. Individually, their efficacy may be limited, but in combination with other components the integrated strategy may be more successful. Experiments in the UK and the Netherlands tested some potential components of such a strategy: presprouting (chitting) and early planting of seed tubers, which should encourage early bulking and evasion of the disease; choice of plant population and configuration to make the crops’ microclimate less favourable for infection. Both early planting and presprouting (chitting) gave higher yields earlier in the season, before late blight put an end to crop growth, and were most effective in years with a short growing season (e.g., when the disease started early). Plant population and spacings within commercially acceptable limits had marked effects on canopy architecture but no effects on late blight infection. However, the effects on tuber size grading were large. At lower densities, tubers were larger on average. This was an advantage when blight infection was early, but could result in the production of too many oversized tubers if it was delayed or absent, unless the crop was defoliated.

Biological Control of Weeds with Antagonistic Plant Pathogens

Many research programs have studied different aspects of the use of antagonistic plant pathogens in biological weed control strategies. The study of effects of individual environmental factors can be regarded as the first step in understanding limitations to the success of biological control methods. This review attempts to address the current advances of the basis and the progress of biocontrol methods, the link between environmental factors and plant infection development, and the use of formulation technology in biological weed control.

Biocontrol of Amaranthus spp. in Europe: state of the art.

Within European COST Action 816, a 5-year collaboration between scientists from 6 European countries has made an important contribution to the previously unstudied insect fauna associated with Amaranthus spp. in Europe. This provides a basis for future introductions of a non-native biocontrol agent into Europe. In addition, two promising microbial herbicides, based on the fungi Alternaria alternata and Trematophoma lignicola have been characterised. Further work on their use in integrated farming systems is required. The use of microbial herbicides in conjunction with new cropping systems, such as green cover crops or living mulch using Trifolium subterraneum is an approach which offers much potential.

Germination of Spotted Spurge (Chamaesyce maculata) Seeds in Response to Different Environmental Factors

Abstract Spotted spurge, a C4 species, is a summer annual weed, introduced to the Golestan province of Iran in 2006. A series of laboratory experiments were conducted at the Faculty of Agriculture, Ferdowsi University of Mashhad, Iran, to evaluate the influence of environmental factors on seed germination of spotted spurge. Seeds germinated over a constant temperature range of 25 to 45 C with a 14-h photoperiod and at 30 to 50 C in continuous darkness. Seeds germinated at alternating day/night temperature regimes of 25/15 to 45/35 C, with maximum germination (> 80%) at alternating day/night temperatures of 35/25, 40/30, and 45/35C. Germination increased from 23.5 to 98% as water potential increased from −0.6 to 0 MPa (control). Germination was > 85% at sodium chloride (NaCl) concentrations up to 80 mM, with no germination at 160 mM NaCl. Germination was not affected by pH, and it was > more than 95% at pH ranging from 4 to 9. The germination of seeds submerged in water for a period less than 3 wk was > 60%, whereas no germination was observed after 9 wk of submergence in water. The results of our study could help to develop effective management strategies for this species. The results also suggest that spotted spurge could invade most tropical regions of Iran. Nomenclature: Spotted spurge, Chamaesyce maculata (L.) Small EPHMA; soybean, Glycine max (L.) Merr.

Characterisation and antifungal activity of silver nanoparticles biologically synthesised by Amaranthus retroflexus leaf extract

ABSTRACT Following the emergence of resistant fungal pathogens, silver nanoparticles (AgNPs) biosynthesized by plants have been recognized as promising tools to combat parasitic fungi. This study evaluated the potency of Amaranthus retroflexus in producing AgNPs, followed by testing their antifungal effects. The AgNPs exhibited a maximum absorption at 430 nm through ultraviolet-visible spectroscopy, while the X-ray diffraction indicated that they were crystal in nature. Fourier transform infrared spectroscopy confirmed the conversion of Ag+ ions to AgNPs due to the reduction by capping material of plant extract. The transmission electron microscope analysis further revealed that the AgNPs were spherical ranging from 10 nm to 32 nm in size. The AgNPs at the concentrations of 50, 100, 200, and 400 μg/mL were applied to the growth of plant, mushroom, and human pathogenic fungi. The 50% minimum inhibitory concentrations (MIC50) against Macrophomina phaseolina, Alternaria alternata and Fusarium oxysporum were observed to be 159.80 ± 14.49, 337.09 ± 19.72, and 328.05 ± 13.29 μg/mL, respectively. However, no considerable inhibition was observed regarding Trichoderma harzianum or Geotrichum candidum. These findings may suggest A. retroflexus as a green solution for biosynthesizing AgNPs with potent antifungal activities against plant pathogenic fungi.