Edward E. Gbur

Degradation and field persistence of imazethapyr.

The volatilization, photolysis, microbial degradation, and field persistence of imazethapyr were studied using formulated and 14C-labeled imazethapyr. Volatilization losses from soil were less than 2%. Photodecomposition losses of up to 8% occurred from soil and up to 52% from a glass slide with no soil. Significantly greater photodecomposition occurred with chain-labeled than ring-labeled 14C-imazethapyr. The amount of 14CO2 evolution from soil treated with either ringor chainlabeled 14C-imazethapyr was not significantly different. The total 14CO2 evolved from the soils ranged from 2.4 to 3.6% of the total 14C-imazethapyr applied to the soil. However, degradation of imazethapyr from the same soils, as determined by high-pressure liquid chromatography, indicated that 62 to 82% of the applied 14C-imazethapyr had been degraded. The degradation rate increased as soil moisture was increased from -100 to -33 kPa. Imazethapyr was more persistent in soil with the higher clay and organic matter content. Nomenclature: Imazethapyr, (?)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxoIH-imidazol-2-ylI]-5-ethyl-3-pyridinecarboxylic acid. Additional index words. Photodecomposition, volatilization, microbial degradation, soil moisture, temperature.

Polyethylene glycol and maltose enhance somatic embryo maturation in loblolly pine (Pinus taeda L.)

SummaryA culture medium that can efficiently produce mature somatic embryos was developed for loblolly pine (Pinus taeda L.). The medium contained maltose as a carbohydrate source and polyethylene glycol as an osmoticum. This medium formulation significantly enhanced embryo maturation efficiency compared to a medium with only maltose, or with sucrose combined with polyethylene glycol. Maltose at 4% and polyethylene glycol at 6% resulted in the highest embryo maturation efficiency; an average of around 100 cotyledonary embryos were produced from 1 g of embryogenic tissue. These results suggested that previous ineffective embryo maturation in loblolly pine may be due to the lack of the proper combination of osmoticum and carbohydrate source. This embryo maturation method also improved morphology of cotyledonary embryos of loblolly pine.

Effect of crop rotation on soil population densities of Fusarium solani and Heterodera glycines and on the development of sudden death syndrome of soybean

Abstract The effect of crop rotation on the development of sudden death syndrome (SDS) of soybean and on the soil population densities of Fusarium solani and the soybean cyst nematode ( Heterodera glycines ) was observed for four years in a field naturally infested with both pathogens. In 1989 all plots were planted to a soybean cultivar susceptible to both pathogens (cv. Lee 74). In 1990 and 1991, the plots were planted to one of the following crops: soybean cv. Lee 74, soybean cv. Hartz 6130 (resistant to both pathogens), sorghum, fescue, or wheat (not double-cropped). In 1992 all plots were planted to soybean cv. Lee 74. The parameters measured to determine rotation effects were severity of SDS over the season, the soil population densities of both pathogens, soybean yields and soybean seed weights. Rotation to any crop except soybean significantly reduced the H. glycines population densities in 1990 and 1991. In 1991, the H. glycines population densities began to rise in the nematode-resistant soybean treatment, but were lower than those in the susceptible soybean treatment. Averaged over all years, the F. solani population densities were significantly lower when sorghum or wheat were grown than when soybean or fescue were grown. Considering the whole season, the F. solani population densities were generally the highest at harvest. Negative correlations between SDS and yield were significant, as were positive correlations between SDS and population densities of F. solani . In 1992, SDS was very low in all treatments, but yields were highest in plots planted to non-soybean crops and lowest in plots planted to the susceptible soybean.

Rice and red rice interference. II. Rice response to population densities of three red rice (Oryza sativa) ecotypes

Abstract Red rice, which grows taller and produces more tillers than domestic rice and shatters most of its seeds early, is a major weed in many rice-growing areas of the world. Field experiments were conducted at Stuttgart, AR in 1997 and 1998 to evaluate the growth response of the Kaybonnet (KBNT) rice cultivar to various population densities of three red rice ecotypes. The ecotypes tested were Louisiana3 (LA3), Stuttgart strawhull (Stgstraw), and Katy red rice (KatyRR). Compared with KBNT alone, LA3, the tallest of the three red rice ecotypes, reduced tiller density of KBNT 51%, aboveground biomass at 91 d after emergence (DAE) 35%, and yield 80%. Stgstraw, a medium-height red rice, reduced KBNT tiller density 49%, aboveground biomass 26%, and yield 61%. KatyRR, the shortest red rice, reduced KBNT tiller density 30%, aboveground biomass 16%, and yield 21%. Tiller density of rice was reduced by 20 to 48% when red rice density increased from 25 to 51 plants m−2. Rice biomass at 91 DAE was reduced by 9 and 44% when red rice densities were 16 and 51 plants m−2. Rice yield was reduced by 60 and 70% at red rice densities of 25 and 51 plants m−2, respectively. These results demonstrate that low populations of red rice can greatly reduce rice growth and yield and that short-statured red rice types may affect rice growth less than taller ecotypes. Nomenclature: Red rice, Oryza sativa L. ORYSA, ‘KatyRR’, ‘LA3’, ‘Stgstraw’; rice, Oryza sativa L., ‘Kaybonnet’.

Nutrient uptake relationship to root characteristics of rice

Data on root parameters and distribution are important for an improved understanding of the factors influencing nutrient uptake by a crop. Therefore, a study was conducted on a Crowley silt loam at the Rice Research and Extension Center near Stuttgart, Arkansas to measure root growth and N, P and K uptake by three rice (Oryza sativa L.) cultivars at active tillering (36 days after emergence (DAE)), maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Soil-root core samples were taken to a depth of 40 cm after plant samples were removed, sectioned into 5 cm intervals, roots were washed from soil and root lengths, dry weights and radii were measured. Root parameters were significantly affected by the soil depth × growth stage interaction. In addition, only root radius was affected by cultivar. At the 0- to 5-cm soil depth, root length density ranged from 38 to 93 cm cm-3 throughout the growing season and decreased with depth to about 2 cm cm-3 in the 35- to 40-cm depth increment. The increase in root length measured with each succeeding growth stage in each soil horizon also resulted in increased root surface area, hence providing more exposed area for nutrient uptake. About 90% of the total root length was found in the 0- to 20-cm soil depth throughout the season. Average root radius measured in the 0- to 5-cm and 35- to 40-cm depth increments ranged from 0.012 to 0.013 cm and 0.004 to 0.005 cm, respectively throughout the season. Total nutrient uptake by rice differed among cultivars only during vegetative growth. Differences in total nutrient uptake among the cultivars in the field appear to be related to absorption kinetics of the cultivars measured in a growth chamber study.

In-Field Movement of Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) and Its Impact on Cotton Lint Yield: Evidence Supporting a Zero-Threshold Strategy

Abstract This research was aimed at understanding how far and how fast glyphosate-resistant (GR) Palmer amaranth will spread in cotton and the consequences associated with allowing a single plant to escape control. Specifically, research was conducted to determine the collective impact of seed dispersal agents on the in-field expansion of GR Palmer amaranth, and any resulting yield reductions in an enhanced GR cotton system where glyphosate was solely used for weed control. Introduction of 20,000 GR Palmer amaranth seed into a 1-m2 circle in February 2008 was used to represent survival through maturity of a single GR female Palmer amaranth escape from the 2007 growing season. The experiment was conducted in four different cotton fields (0.53 to 0.77 ha in size) with no history of Palmer amaranth infestation. In the subsequent year, Palmer amaranth was located as far as 114 m downslope, creating a separate patch. It is believed that rainwater dispersed the seeds from the original area of introduction. In less than 2 yr after introduction, GR Palmer amaranth expanded to the boundaries of all fields, infesting over 20% of the total field area. Spatial regression estimates indicated that no yield penalty was associated with Palmer amaranth density the first year after introduction, which is not surprising since only 0.56% of the field area was infested with GR Palmer amaranth in 2008. Lint yield reductions as high as 17 kg ha−1 were observed 2 yr after the introduction (in 2009). Three years after the introduction (2010), Palmer amaranth infested 95 to 100% of the area in all fields, resulting in complete crop loss since it was impossible to harvest the crop. These results indicate that resistance management options such as a “zero-tolerance threshold” should be used in managing or mitigating the spread of GR Palmer amaranth. This research demonstrates the need for proactive resistance management. Nomenclature: Glyphosate; Palmer amaranth, Amaranthus palmeri S. Wats.; cotton, Gossypium hirsutum L. ‘Stoneville 4554 B2/RRF’.

Effect of basal medium, growth regulators and Phytagel concentration on initiation of embryogenic cultures from immature zygotic embryos of loblolly pine (Pinus taeda L.)

Abstract Low initiation frequency is one of the main barriers in applying somatic embryogenesis to the clonal production of Pinus species. Factors affecting initiation, including basal medium, plant growth regulators, and Phytagel concentration, have been investigated in loblolly pine (Pinus taeda L.). BM1 basal medium proved superior to DCR1 and LP (LP basal salts plus BM1 organic nutrients). No extrusion from megagametophytes was exhibited on LP medium. The combination of 3 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.5 mg/l 6-benzylaminopurine (BA) resulted in a higher extrusion frequency than that of 11 mg/l 2,4-D, 4.5 mg/l BA and 4.3 mg/l kinetin. Phytagel at 1 g/l resulted in the highest explant browning, but the lowest extrusion frequency, while 4 g/l Phytagel induced some dry embryogenic extrusions. Phytagel at 2 g/l was regarded as the best level for initiation of embryogenic cultures.

Evidence for allelopathic interference of Japanese honeysuckle (Lonicera japonica) to loblolly and shortleaf pine regeneration

Abstract Japanese honeysuckle presents a serious problem to the economically attractive natural regeneration of loblolly and shortleaf pine. This research investigated the potential allelopathic interference mechanisms of Japanese honeysuckle in relation to pine regeneration and growth, which may provide insight into overcoming this problem. The allelopathic potential of root exudates and leaf litter from Japanese honeysuckle was tested against loblolly and shortleaf pine seedlings. When Japanese honeysuckle and loblolly pine seedlings were grown using the same irrigation reservoir, there was no significant effect on the growth of either pine species. Exudates of Japanese honeysuckle grown as a pure culture in donor cups also produced no growth effects on pure-cultured pine seedlings grown in acceptor cups. In other assays, aqueous extracts of Japanese honeysuckle leaf tissue were toxic to duckweeds at concentrations well below levels where plasmolysis might cause effects. When Japanese honeysuckle leaf tissue was added to soil at a rate of 2 g tissue 100 g−1 soil, mean seedling height at 128 d after planting was reduced by as much as 40%. Moreover, pine seedlings grown in the presence of Japanese honeysuckle tissue exhibited significant chlorosis of the shoot and needles. Gas chromatography–mass spectroscopy analyses and high-performance liquid chromatography of Japanese honeysuckle leaf tissue aqueous extracts confirmed the presence of five compounds previously identified as possible allelochemicals: 4-hydroxycinnamic acid; 2-hydroxycinnamic acid; 3,4-dihydroxybenzoic acid; 3,4-dihydroxycinnamic acid; and chlorogenic acid. Results indicate that allelopathy plays at least a partial role in Japanese honeysuckle interference with loblolly and shortleaf pine. Nomenclature: Japanese honeysuckle, Lonicera japonica Thunb.; loblolly pine, Pinus taeda L.; shortleaf pine, Pinus echinata Mill; duckweed, Lemna minor L.

Residue Management Practice Effects on Soil Surface Properties in a Young Wheat-Soybean Double-Crop System

ABSTRACT Approximately 25% of the soybean [Glycine max (L.) Merr.] grown in the mid-South is produced in a wheat (Triticum aestivum L.)-soybean double-crop system. Pre-soybean field preparations often consist of removing wheat residue by burning followed by conventional tillage (CT). However, crop residue burning has serious negative environmental consequences and will likely be outlawed in the future. Therefore, the objective of this study was to evaluate the short-term effects of alternative wheat-residue management practices, tillage [no-tillage (NT) and CT], burning (burn and no burn), and wheat-residue level (low and high), on soil surface properties after two full cropping cycles in a wheat-soybean double-crop production system on two silt-loam Alfisols in east-central Arkansas. Soil bulk density increased over time, but the increase was unaffected by imposed treatments. Changes in soil pH and electrical conductivity (EC) were generally unaffected by tillage or burning, whereas soil EC increased by 7% under the high and decreased by 8% under the low wheat-residue level treatment at one location, but not the other. Mehlich-3-extractable Mg and Zn increased more and Na decreased less under NT than CT at one location or the other. Soil organic matter and total N and C also increased more under NT than CT at one location, but not the other. The results of this study indicate that, in a wheat-soybean double-crop production system in a relatively warm and wet environment, numerous soil properties can be improved more under NT than CT and more when crop residues are left unburned than when they are removed by burning. Extended use of alternative wheat-residue management practices that improve soil tilth will result in more sustainable agriculture and likely increase production.

Vertical and temporal distribution of Fusarium solani and Heterodera glycines in fields with sudden death syndrome of soybean

Abstract Sudden death syndrome (SDS) is an important soilborne disease of soybean caused by the fungus Fusarium solani . This disease is also associated with the soybean cyst nematode (SCN), Heterodera glycines . To quantify the vertical and temporal distribution of these pathogens in the soil profile, a study was conducted at the University of Arkansas Pine Tree (PTS) and Cotton Branch Stations (CBS) in 1991. Soil samples were taken at six depths (0 to 7, 7 to 15, 15 to 30, 30 to 50, 50 to 75 and 75 to 100 cm) at four growth stages (planting, R2, R6 and harvest) and numbers of F. solani , SCN and total fungi were determined. Soil physical and chemical characteristics were measured at planting and soybean root densities were measured at R2 and R6. Disease development was followed weekly in August and September. Soil numbers of F. solani were greatest in the top 15 cm of soil throughout the season. SCN egg numbers also were greatest in this zone until harvest. At harvest, numbers significantly increased at depths of at least 50 cm. The greatest root densities were in the 0- to 15-cm zone. At both locations, the 0- to 15-cm zone was over a plow pan under which the pH decreased from 6.4 to 7.0 above the pan to 3.8 to 4.5 below the pan. Total fungal numbers were greatest in the upper soil layers at planting but declined until there were no significant differences in numbers of total fungi with depth from R2 to harvest. SDS developed sooner and was more severe at PTS than at CBS. PTS had greater numbers of F. solani but supported lower numbers of SCN at the end of the season than CBS.