Browsing by Author "Johnson, Charles"
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- Brewer’s Spent Grain with Yeast Amendment Shows Potential for Anaerobic Soil Disinfestation of Weeds and Pythium irregulareLiu, Danyang; Samtani, Jayesh; Johnson, Charles; Zhang, Xuemei; Butler, David M.; Derr, Jeffrey (MDPI, 2023-08-08)Anaerobic soil disinfestation (ASD) is a promising alternative to chemical fumigation for controlling soilborne plant pathogens and weeds. This study investigated the impact of brewer’s spent grain (BSG), a locally available carbon source, on various weed species and the oomycete pathogen Pythium irregulare in ASD. Two greenhouse studies were conducted using BSG and yeast at full and reduced rates in a completely randomized design with four replicates and two runs per study. In both studies, ASD treatments significantly decreased the seed viability of all weed species and the Pythium irregulare inoculum, while promoting higher cumulative anaerobicity compared to the non-treated control. The addition of yeast had a notable effect when combined with BSG but not with rice bran. When used in reduced carbon rates, yeast supplementation enhanced the efficacy of BSG, providing comparable control to the full rate for most weed species, including redroot pigweed, white clover, and yellow nutsedge. Interestingly, no ASD treatment affected the soil temperature. Furthermore, BSG treatments caused higher concentrations of volatile fatty acids compared to ASD with rice bran and the non-treated control. This finding suggests that the inclusion of yeast in ASD shows potential for reducing the carbon input required for effective soil disinfestation.
- Morphological characterization of the tobacco cyst nematode complex, Globodera tabacum sspp. tabacum, virginiae, and solanacearum (Nemata: Heteroderinae)Mota, Manuel M. (Virginia Tech, 1992)A morphological and morphometrical study was made of the tobacco cyst nematode complex, Globodera tabacum sspp. tabacum (GTT), virginiae (GTV), and solanacearum (GTS) including observations of eggs, second-stage juveniles (J2), males, females, and cysts. Observations focused on the anterior region including head shape, lip pattern, stylet morphology, and the tail region including tail shape in J2 and spicules in males. The head region of J2 was set off from the body and consisted of three head annules, six lips, and an oral disk. The shape of the head seen in lateral view showed little variability within or among the subspecies. Stylets of J2 were robust and had three anchor-shaped, rounded knobs. They varied slightly in width and height within each subspecies. The lip region consisted of a central oral disc surrounded by two lateral and two submedial lips. The oral disc varied from rectangular to elliptical. The submedial lip pairs were not fused in all specimens. The tail of J2 was finely pointed and the tip was rounded in all subspecies. The head of the male was set off and contained five head annules, six lips, and an oral disc. The head region was similar in lateral view in all three subspecies. The stylet was robust and had three rounded knobs that slope posteriorly. The dorsal knob of males of GTV appeared to slope more posteriorly than in the other two subspecies. In the SEM, the head region had a large central rounded to elliptical oral disc with two lateral and two submedial lip pairs. The submedial lips were rounded or rectangular. The submedial lip pairs were fused in most specimens, but not all. The spicules of GTT showed a slightly more enlarged head region than the other two subspecies. The three subspecies could not be separated on the basis of any character or group of characters of J2 or males.The anterior region including body shape, head shape, lip pattern, stylet morphology, and the terminal area in females; and body shape and terminal area of cysts were observed. The most useful characters to separate the three subspecies were female body shape, stylet knobs, perineal tubercles, cyst shape, anal-fenestral ridge pattern, anus, and tail region. GTT was characterized by rounded females and cysts with sharply back sloped stylet knobs, clumped perineal tubercles in the vulval region, tight parallel ridges in the anal-fenestral region of the cyst, and a distinct tail region not shaped like a crescent. GTV was characterized by its ovoid to ellipsoid female and cyst shape, the "Dutch shoe" shape of the dorsal stylet knob, the more individualized perineal tubercles, a maze-like pattern of ridges in the anal-fenestral region, and an indistinct anus. GTS was characterized by its ovoid to ellipsoid female and cyst shape, moderately backward sloped stylet knobs, more widely separated ridges, a distinct anus, and a tail region usually shaped like a crescent. Much variability in shape and patterns was visible among all the isolates of the different subspecies. Tubercles in the neck as well as bullae were reported and discussed. A morphometric evaluation of second-stage juveniles (J2), males, females, and cysts was performed for several characters. Morphometrics of eggs, J2, and males were considerably less variable than in females and cysts. No measurements of eggs and J2 were useful for identification of the three subspecies. The distance of the median bulb to the head end and the distance of the excretory pore to the head end in J2 and males were quite reliable and useful. The stylet knob width of males was useful for identifying GTV isolates. Tail length was useful in separating males of GTT isolates from GTV and GTS. The body length/ width (L/W) ratio of females and cysts discriminated GTT from GTV and GTS. Stylet knob width of females was an auxiliary character useful for identifying GTV. This subspecies complex has a continuum of values for the majority of the characters observed. The data suggests a closer relationship between GTV and GTS which is likely because these two subspecies occur in very close proximity in Virginia, 38 km separation between closest adjacent geographical ranges; whereas GTT occurs 700 km away in the northeastern U.S.
- Nitrification inhibition by metalaxyl as influenced by pH, temperature, and moisture content in three soilsMoore, J. Michael (Virginia Polytechnic Institute and State University, 1989)Metalaxyl, [N—(2,6-Dimethylphenyl)-N-(Methoxyacetyl)-alanine methyl ester], is used extensively in tobacco (Nicotiana tabacum L.) production for prevention of black shank (Phytophthora parasitica Dast. var. nicotianae), blue mold (Peronospora tabacina Adam), and damping-off (Pythigm spp.). Metalaxyl is also patented as a nitrification inhibitor, although not marketed for that purpose. Proper maturity and ripening of flue-cured tobacco depends on an adequate supply of N through the time of removal of the inflorescence, with a declining supply of N from that point. Use of a chemical which might prolong the availability of N in tobacco could delay maturity and reduce the quality of the cured leaf. These studies were conducted to determine whether metalaxyl might inhibit nitrification under a broad range of soil physical and environmental conditions prevalent in the tobacco producing areas of Virginia. The influence of soil type, soil pH, soil temperature, and soil moisture on inhibition of nitrification by metalaxyl (1 mg kg⁻¹) were investigated in three soils used extensively for tobacco production. Soils used in the study were Cecil sandy loam (clayey, kaolinitic, thermic Typic Hapludult), Appomattox fine sandy loam (clayey, mixed, thermic Typic Kandhapludult), and Mattoponi sandy loam (clayey, mixed, thermic Typic Hapludult). Metalaxyl did not inhibit nitrification under any of the conditions studied. However, NO₂⁻ accumulation with metalaxyl was sometimes greater than the control, especially at high pH (7.0) in the Cecil and Appomattox soils, and at 10 and 20°C. Nitrite and NO₃⁻ accumulations from four rates of metalaxyl (1, 5, 25, and 125 mg kg⁻¹) were compared with those of an untreated control and a nitrapyrin standard over a seven week soil incubation period in further studies using the same soils and adjusted pH levels. Significant NO₂⁻ accumulation occurred during the first week after treatment at high pH in all soil types, with 5, 25, and 125 mg kg⁻¹ metalaxyl. Only the 125 mg kg⁻¹ metalaxyl treatment caused NO₂⁻ accumulation at the high pH in all soils beyond the second week after treatment, with the peak occurring in most cases between weeks three and four. Nitrate accumulation proceeded normally in all soil types and pH levels except with treatments of 25 and 125 mg kg". Nitrate accumulations with 25 mg kg⁻¹ were similar to those for nitrapyrin. The 125 mg kg⁻¹ rate was consistent in causing near total inhibition of NO₃⁻ accumulation at all pH levels in all soils. Nitrate accumulation tended to be lower at lower soil pH levels compared to the highest pH for all soils. Little difference in nitrification due to soil appears to be evident. Use of metalaxyl at recommended rates of 0.25 to 1.5 mg kg⁻¹ would not be expected to inhibit nitrification.