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Agronomy, Volume 3, Issue 3 (September 2013), Pages 508-582

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Open AccessArticle Root Characteristics of Perennial Warm-Season Grasslands Managed for Grazing and Biomass Production
Agronomy 2013, 3(3), 508-523; doi:10.3390/agronomy3030508
Received: 22 May 2013 / Revised: 25 June 2013 / Accepted: 25 June 2013 / Published: 8 July 2013
Cited by 3 | PDF Full-text (723 KB) | HTML Full-text | XML Full-text
Abstract
Minirhizotrons were used to study root growth characteristics in recently established fields dominated by perennial C4-grasses that were managed either for cattle grazing or biomass production for bioenergy in Virginia, USA. Measurements over a 13-month period showed that grazing resulted in smaller total
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Minirhizotrons were used to study root growth characteristics in recently established fields dominated by perennial C4-grasses that were managed either for cattle grazing or biomass production for bioenergy in Virginia, USA. Measurements over a 13-month period showed that grazing resulted in smaller total root volumes and root diameters. Under biomass management, root volume was 40% higher (49 vs. 35 mm3) and diameters were 20% larger (0.29 vs. 0.24 mm) compared to grazing. While total root length did not differ between grazed and biomass treatments, root distribution was shallower under grazed areas, with 50% of total root length in the top 7 cm of soil, compared to 41% in ungrazed exclosures. These changes (i.e., longer roots and greater root volume in the top 10 cm of soil under grazing but the reverse at 17–28 cm soil depths) were likely caused by a shift in plant species composition as grazing reduced C4 grass biomass and allowed invasion of annual unsown species. The data suggest that management of perennial C4 grasslands for either grazing or biomass production can affect root growth in different ways and this, in turn, may have implications for the subsequent carbon sequestration potential of these grasslands. Full article
Open AccessArticle Large Genetic Variability in Chickpea for Tolerance to Herbicides Imazethapyr and Metribuzin
Agronomy 2013, 3(3), 524-536; doi:10.3390/agronomy3030524
Received: 25 March 2013 / Revised: 23 June 2013 / Accepted: 12 July 2013 / Published: 22 July 2013
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Abstract
Chickpea (Cicer arietinum L.) is known to be sensitive to many herbicides and, therefore, choices for using post-emergence herbicides for weed control are limited. The present study was aimed at identifying sources of tolerance to two herbicides with different modes of action
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Chickpea (Cicer arietinum L.) is known to be sensitive to many herbicides and, therefore, choices for using post-emergence herbicides for weed control are limited. The present study was aimed at identifying sources of tolerance to two herbicides with different modes of action (imazethapyr—amino acid synthesis inhibitor; and metribuzin—photosynthesis inhibitor) for use in breeding herbicide tolerant cultivars. Screening of 300 diverse chickpea genotypes (278 accessions from the reference set and 22 breeding lines) revealed large genetic variations for tolerance to herbicides imazethapyr and metribuzin. In general, the sensitivity of the genotypes to metribuzin was higher compared to that for imazethapyr. Several genotypes tolerant to metribuzin (ICC 1205, ICC 1164, ICC 1161, ICC 8195, ICC 11498, ICC 9586, ICC 14402 ICC 283) and imazethapyr (ICC 3239, ICC 7867, ICC 1710, ICC 13441, ICC 13461, ICC 13357, ICC 7668, ICC 13187) were identified, based on average herbicide tolerance scores from two experimental locations each. The herbicide tolerant lines identified in this study will be useful resources for development of herbicide tolerant cultivars and for undertaking genetic and physiological studies on herbicide tolerance in chickpea. Full article
(This article belongs to the Special Issue Weed Management and Herbicide Resistance)
Open AccessArticle Implications of Environmental Stress during Seed Development on Reproductive and Seed Bank Persistence Traits in Wild Oat (Avena fatua L.)
Agronomy 2013, 3(3), 537-549; doi:10.3390/agronomy3030537
Received: 2 July 2013 / Revised: 19 July 2013 / Accepted: 24 July 2013 / Published: 30 July 2013
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Abstract
Weeds produce seed under a wide range of conditions, depending on timing of emergence, prevailing crop, soil microsites, and climatic conditions, among other factors. We hypothesized that the maturation environment during weed seed development will influence reproductive allocation and seed persistence traits, such
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Weeds produce seed under a wide range of conditions, depending on timing of emergence, prevailing crop, soil microsites, and climatic conditions, among other factors. We hypothesized that the maturation environment during weed seed development will influence reproductive allocation and seed persistence traits, such as seed dormancy and vigor, and needs to be considered when formulating weed management strategies. This research evaluated the effects of shade and drought stress on reproductive allocation, seed dormancy and seed vigor in select lines of wild oat (Avena fatua L.). Plants were grown in the greenhouse under drought stress and shade. Harvested seed were subjected to controlled after-ripening and aging regimes. Drought and shade reduced reproductive allocation and resulted in seed with less intense primary dormancy compared to the plants grown under resource-rich conditions, but had no apparent effect on seed vigor. Our data provide additional support to the hypothesis that seed dormancy within a species is a highly plastic trait that can be strongly influenced by the growth conditions of the mother plant. Such plasticity may have important implications for establishing ecologically-based weed control criteria on which threshold-based weed management systems are implemented. Full article
(This article belongs to the Special Issue Weed Management and Herbicide Resistance)
Open AccessArticle Effects of Pseudomonas fluorescens on the Water Parameters of Mycorrhizal and Non-Mycorrhizal Seedlings of Pinus halepensis
Agronomy 2013, 3(3), 571-582; doi:10.3390/agronomy3030571
Received: 9 May 2013 / Revised: 2 August 2013 / Accepted: 2 August 2013 / Published: 20 August 2013
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Abstract
Inoculation of forest seedlings with mycorrhizal fungi and rhizobacteria can improve the morphological and physiological qualities of plants, especially those used for regeneration of arid areas. In this paper, under standard nursery conditions, Aleppo pine seedlings were inoculated with Pseudomonas fluorescens CECT 5281
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Inoculation of forest seedlings with mycorrhizal fungi and rhizobacteria can improve the morphological and physiological qualities of plants, especially those used for regeneration of arid areas. In this paper, under standard nursery conditions, Aleppo pine seedlings were inoculated with Pseudomonas fluorescens CECT 5281 rhizobacteria. Some of these seedlings were also inoculated with the ectomycorrhizal fungus Pisolithus tinctorius. Five months after the inoculations, we examined the growth, water parameters (osmotic potential at full turgor [Ψπfull], osmotic potential at zero turgor [Ψπ0], and the tissue modulus of elasticity near full turgor [Emax]), mycorrhizal colonisation, and concentration of macronutrients (N, P, K, Ca and Mg) in the seedlings. Subsequently, a trial was conducted to assess the root growth potential. P. fluorescens CECT 5281 decreased the cellular osmotic potential of P. halepensis seedlings but increased its elasticity. P. tinctorius + P. fluorescens caused osmotic adjustment at zero turgor and increased tissue elasticity, which improved tolerance to water stress. All inoculations improved the growth and nutrition of the seedlings but caused non-significant effects on root growth potential. The co-inoculation Pisolithus tinctorius + Pseudomonas fluorescens at the nursery may be a suitable technique for producing improved seedling material for restoration purposes. Full article

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Open AccessDiscussion The Cysteine Protease–Cysteine Protease Inhibitor System Explored in Soybean Nodule Development
Agronomy 2013, 3(3), 550-570; doi:10.3390/agronomy3030550
Received: 29 May 2013 / Revised: 12 July 2013 / Accepted: 22 July 2013 / Published: 20 August 2013
Cited by 5 | PDF Full-text (931 KB) | HTML Full-text | XML Full-text
Abstract
Almost all protease families have been associated with plant development, particularly senescence, which is the final developmental stage of every organ before cell death. Proteolysis remobilizes and recycles nitrogen from senescent organs that is required, for example, seed development. Senescence-associated expression of proteases
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Almost all protease families have been associated with plant development, particularly senescence, which is the final developmental stage of every organ before cell death. Proteolysis remobilizes and recycles nitrogen from senescent organs that is required, for example, seed development. Senescence-associated expression of proteases has recently been characterized using large-scale gene expression analysis seeking to identify and characterize senescence-related genes. Increasing activities of proteolytic enzymes, particularly cysteine proteases, are observed during the senescence of legume nodules, in which a symbiotic relationship between the host plant and bacteria (Rhizobia) facilitate the fixation of atmospheric nitrogen. It is generally considered that cysteine proteases are compartmentalized to prevent uncontrolled proteolysis in nitrogen-fixing nodules. In addition, the activities of cysteine proteases are regulated by endogenous cysteine protease inhibitors called cystatins. These small proteins form reversible complexes with cysteine proteases, leading to inactivation. However, very little is currently known about how the cysteine protease-cysteine protease inhibitor (cystatin) system is regulated during nodule development. Moreover, our current understanding of the expression and functions of proteases and protease inhibitors in nodules is fragmented. To address this issue, we have summarized the current knowledge and techniques used for studying proteases and their inhibitors including the application of “omics” tools, with a particular focus on changes in the cysteine protease-cystatin system during nodule development. Full article

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