Horseweed is traditionally considered a non-cropland weed. However, populations resistant to glyphosate have eventually become established in no-till agronomic cropping systems. Growth chamber and greenhouse experimen...Horseweed is traditionally considered a non-cropland weed. However, populations resistant to glyphosate have eventually become established in no-till agronomic cropping systems. Growth chamber and greenhouse experiments were conducted to compare selected biological and physiological parameters of glyphosate-resistant (GR) and -susceptible (GS) horseweed biotypes from Mississippi with a broader goal of fitness characterization in these biotypes. Vegetative growth parameters (number of leaves, rosette diameter and area, shoot and root fresh weights) were recorded weekly from 5 to 11 wk after emergence and reproductive attributes [days to bolting (production of a flowering stalk) and flowering] and senescence were measured for both GR and GS biotypes under high (24°C/20°C) and low (18°C/12°C) temperature regimes, both with a 13-h light period. Physiological traits such as net photosynthesis, phenolic content, and cell membrane thermostability, all in the presence and absence of glyphosate, and leaf content of divalent cations such as Ca2+ and Mg2+ were assayed in the two biotypes under the high temperature regime. All horseweed vegetative growth parameters except root fresh weight were higher in the high temperature regime compared to that in low temperature regime in both biotypes. Number of leaves, rosette diameter and area, shoot and root fresh weight were 40 vs. 35, 9.3 vs. 8.7 cm, 51 vs. 43 cm2, 3.7 vs. 3.2 g, and 3.5 vs. 4.2 g under high and low temperature conditions, respectively, when averaged across biotypes and weekly measurements. All growth parameters listed above were higher for the GR biotype compared to the GS biotype. Number of leaves, rosette diameter and area, shoot and root fresh weight were 38 vs. 37, 9.1 vs. 8.9 cm, 50.2 vs. 44 cm2, 3.9 vs. 3.1 g, and 4.3 vs. 3.5 g for GR and GS biotypes, respectively, averaged across the temperature treatments and weekly measurements. Reproductive developmental data of these biotypes indicated that the GS biotype bolted earlier than the GR biotype. The GS biotype had more phenolic content and exhibited higher cell membrane thermostability, but less net photosynthetic rate compared to the GR biotype. At 48 h after treatment with glyphosate, there was no change in phenolic content of both GR and GS biotypes. However, glyphosate reduced cell membrane thermostability and net photosynthetic rate more in the GS biotype than that in the GR biotype. Chemical analysis of GR and GS leaf tissue did not reveal any differences in levels of divalent cations such as Ca2+ and Mg2+. Further studies are needed to determine if some of the differences between the two biotypes observed above relate to fitness variation in a natural environment.展开更多
Winter flooding of harvested rice fields attracts migratory waterfowl and may assist in degrading rice straw residue. Field studies were conducted between 2003 and 2005 in Stoneville, MS to evaluate the impacts of win...Winter flooding of harvested rice fields attracts migratory waterfowl and may assist in degrading rice straw residue. Field studies were conducted between 2003 and 2005 in Stoneville, MS to evaluate the impacts of winter flooding of harvested rice fields on rice straw degradation, winter weeds, soybean yield, and soil biochemical and chemical properties. The experimental area each year consisted of a harvested rice field that remained no-till after harvest and that was dissected into 7.6- by 15-m bays with constructed levees to accommodate winter flooding treatments. Flooding treatments (10-cm depth) consisted of: 1) flooded from mid-October to early March;2) flooded mid-October to early January;3) flooded mid-December to early March;4) flooded mid-December to mid-January;and 5) no flood. Winter weeds were counted, biomass determined as well as residual rice straw before flooding and in early April of each year. Winter flooding reduced rice straw biomass 32% to 60% compared to 21% to 31% reduction for no winter flood with the longest flood duration resulting in the greatest loss of carbon and nitrogen from straw residues in both years. Winter flooding treatments reduced weed populations and weed biomass from 43% to 99% when compared to no flooding treatment. Soybean yields ranged from 3295 kg.ha-1 with the longest winter flooding regime to 4295 kg.ha-1 with no flooding. Significant reductions in soil nitrate levels were most consistent in the upper 0 to 2.5-cm surface soil. Soil enzymatic activity (dehydrogenase and fluorescein diacetate hydrolysis) was increased by flooding in 2003, while minimal effects were found in the second year consistent with more anaerobic conditions attained in 2003 compared to 2004. Environmental benefits of accelerated straw decomposition and weed control is achieved by winter flooding;however, there are negative consequences of nitrogen losses and reduced soybean yield.展开更多
文摘Horseweed is traditionally considered a non-cropland weed. However, populations resistant to glyphosate have eventually become established in no-till agronomic cropping systems. Growth chamber and greenhouse experiments were conducted to compare selected biological and physiological parameters of glyphosate-resistant (GR) and -susceptible (GS) horseweed biotypes from Mississippi with a broader goal of fitness characterization in these biotypes. Vegetative growth parameters (number of leaves, rosette diameter and area, shoot and root fresh weights) were recorded weekly from 5 to 11 wk after emergence and reproductive attributes [days to bolting (production of a flowering stalk) and flowering] and senescence were measured for both GR and GS biotypes under high (24°C/20°C) and low (18°C/12°C) temperature regimes, both with a 13-h light period. Physiological traits such as net photosynthesis, phenolic content, and cell membrane thermostability, all in the presence and absence of glyphosate, and leaf content of divalent cations such as Ca2+ and Mg2+ were assayed in the two biotypes under the high temperature regime. All horseweed vegetative growth parameters except root fresh weight were higher in the high temperature regime compared to that in low temperature regime in both biotypes. Number of leaves, rosette diameter and area, shoot and root fresh weight were 40 vs. 35, 9.3 vs. 8.7 cm, 51 vs. 43 cm2, 3.7 vs. 3.2 g, and 3.5 vs. 4.2 g under high and low temperature conditions, respectively, when averaged across biotypes and weekly measurements. All growth parameters listed above were higher for the GR biotype compared to the GS biotype. Number of leaves, rosette diameter and area, shoot and root fresh weight were 38 vs. 37, 9.1 vs. 8.9 cm, 50.2 vs. 44 cm2, 3.9 vs. 3.1 g, and 4.3 vs. 3.5 g for GR and GS biotypes, respectively, averaged across the temperature treatments and weekly measurements. Reproductive developmental data of these biotypes indicated that the GS biotype bolted earlier than the GR biotype. The GS biotype had more phenolic content and exhibited higher cell membrane thermostability, but less net photosynthetic rate compared to the GR biotype. At 48 h after treatment with glyphosate, there was no change in phenolic content of both GR and GS biotypes. However, glyphosate reduced cell membrane thermostability and net photosynthetic rate more in the GS biotype than that in the GR biotype. Chemical analysis of GR and GS leaf tissue did not reveal any differences in levels of divalent cations such as Ca2+ and Mg2+. Further studies are needed to determine if some of the differences between the two biotypes observed above relate to fitness variation in a natural environment.
文摘Winter flooding of harvested rice fields attracts migratory waterfowl and may assist in degrading rice straw residue. Field studies were conducted between 2003 and 2005 in Stoneville, MS to evaluate the impacts of winter flooding of harvested rice fields on rice straw degradation, winter weeds, soybean yield, and soil biochemical and chemical properties. The experimental area each year consisted of a harvested rice field that remained no-till after harvest and that was dissected into 7.6- by 15-m bays with constructed levees to accommodate winter flooding treatments. Flooding treatments (10-cm depth) consisted of: 1) flooded from mid-October to early March;2) flooded mid-October to early January;3) flooded mid-December to early March;4) flooded mid-December to mid-January;and 5) no flood. Winter weeds were counted, biomass determined as well as residual rice straw before flooding and in early April of each year. Winter flooding reduced rice straw biomass 32% to 60% compared to 21% to 31% reduction for no winter flood with the longest flood duration resulting in the greatest loss of carbon and nitrogen from straw residues in both years. Winter flooding treatments reduced weed populations and weed biomass from 43% to 99% when compared to no flooding treatment. Soybean yields ranged from 3295 kg.ha-1 with the longest winter flooding regime to 4295 kg.ha-1 with no flooding. Significant reductions in soil nitrate levels were most consistent in the upper 0 to 2.5-cm surface soil. Soil enzymatic activity (dehydrogenase and fluorescein diacetate hydrolysis) was increased by flooding in 2003, while minimal effects were found in the second year consistent with more anaerobic conditions attained in 2003 compared to 2004. Environmental benefits of accelerated straw decomposition and weed control is achieved by winter flooding;however, there are negative consequences of nitrogen losses and reduced soybean yield.
