Edzard Van Santen

Annual bluegrass (Poa annua) populations exhibit variation in germination response to temperature, photoperiod, and fenarimol

Abstract Laboratory studies were conducted to evaluate variation in germination response of eight annual bluegrass ecotypes (‘Augusta 4’, ‘Augusta 8’, ‘Augusta 14’, ‘Augusta 17’, ‘Auburn’, ‘Birmingham’, ‘Columbia’, and ‘Purchased’) to photoperiod, temperature, and fenarimol, a fungicide–herbicide used for preemergence annual bluegrass. Seed collected from greenhouse-grown plants and stored for > 2 mo were evaluated under 18 environments (three day and night temperatures by six day and night durations). There was a significant ecotype by environment interaction affecting annual bluegrass germination. High temperature markedly restricted germination, with only the Birmingham ecotype exceeding 20% germination at day and night temperatures of 39 and 29 C, respectively. Maximum germination of all ecotypes was observed at a day and night temperature of 19 and 10 C, respectively. Maximum germination for a specific photoperiod was not consistent across ecotypes; however, all ecotypes germinated to some degree in complete darkness, which indicates that maintaining a dense turf canopy to eliminate annual bluegrass germination may not be completely effective. Ecotypes did not differ with respect to root length response to fenarimol but did vary with respect to shoot length response. Purchased and Columbia shoot growth were the most tolerant to increasing fenarimol concentrations. This information will be used to develop improved management strategies for annual bluegrass. Nomenclature: Fenarimol, α-(2-chlorophenyl)-α-(4-chlorophenyl)-5-pyrimidine-methanol; annual bluegrass, Poa annua var. annua (L.) Timm. and Poa annua var. reptans (Hauskn.) Timm. POANN.

Synergistic interactions between Cry1Ac and natural cotton defenses limit survival of Cry1Ac-resistant Helicoverpa zea (Lepidoptera: Noctuidae) on Bt cotton.

Larvae of the bollworm Helicoverpa zea (Boddie) show some tolerance to Bacillus thuringiensis (Bt) Cry1Ac, and can survive on Cry1Ac-expressing Bt cotton, which should increase resistance development concerns. However, field-evolved resistance has not yet been observed. In a previous study, a population of H. zea was selected for stable resistance to Cry1Ac toxin. In the present study, we determined in laboratory bioassays if larvae of the Cry1Ac toxin-resistant H. zea population show higher survival rates on field-cultivated Bt cotton squares (= flower buds) collected prebloom—bloom than susceptible H. zea. Our results show that Cry1Ac toxin-resistant H. zea cannot complete larval development on Cry1Ac-expressing Bt cotton, despite being more than 150-fold resistant to Cry1Ac toxin and able to survive until pupation on Cry1Ac toxin concentrations greater than present in Bt cotton squares. Since mortality observed for Cry1Ac-resistant H. zea on Bt cotton was higher than expected, we investigated whether Cry1Ac interacts with gossypol and or other compounds offered with cotton powder in artificial diet. Diet incorporation bioassays were conducted with Cry1Ac toxin alone, and with gossypol and 4% cotton powder in the presence and absence of Cry1Ac. Cry1Ac toxin was significantly more lethal to susceptible H. zea than to resistant H. zea, but no difference in susceptibility to gossypol was observed between strains. However, combinations of Cry1Ac with gossypol or cotton powder were synergistic against resistant, but not against susceptible H. zea. Gossypol concentrations in individual larvae showed no significant differences between insect strains, or between larvae fed gossypol alone vs. those fed gossypol plus Cry1Ac. These results may help explain the inability of Cry1Ac-resistant H. zea to complete development on Bt cotton, and the absence of field-evolved resistance to Bt cotton by this pest.

The Bacterial Pathogen Xylella fastidiosa Affects the Leaf Ionome of Plant Hosts during Infection

Xylella fastidiosa is a plant pathogenic bacterium that lives inside the host xylem vessels, where it forms biofilm believed to be responsible for disrupting the passage of water and nutrients. Here, Nicotiana tabacum was infected with X. fastidiosa, and the spatial and temporal changes in the whole-leaf ionome (i.e. the mineral and trace element composition) were measured as the host plant transitioned from healthy to diseased physiological status. The elemental composition of leaves was used as an indicator of the physiological changes in the host at a specific time and relative position during plant development. Bacterial infection was found to cause significant increases in concentrations of calcium prior to the appearance of symptoms and decreases in concentrations of phosphorous after symptoms appeared. Field-collected leaves from multiple varieties of grape, blueberry, and pecan plants grown in different locations over a four-year period in the Southeastern US showed the same alterations in Ca and P. This descriptive ionomics approach characterizes the existence of a mineral element-based response to X. fastidiosa using a model system suitable for further manipulation to uncover additional details of the role of mineral elements during plant-pathogen interactions. This is the first report on the dynamics of changes in the ionome of the host plant throughout the process of infection by a pathogen.

Breeding Objectives in Forages

All breeding programs share one common objective – to improve a species for use within a target population of environments and a particular agricultural context. Beyond this common goal, the objectives of forage breeding programs are as varied as the species upon which they are based and the breeders who develop and implement them. Many breeding objectives are determined a priori by the choice of a species with one or more obvious trait limitations or deficiencies, such as poor seedling vigor, synthesis of toxic alkaloids, or severe susceptibility to a major pest. For species without such limitations, breeders have the luxury of defining less stringent and/or more flexible breeding objectives.

Nontuberous Sedge and Kyllinga Species' Response to Herbicides1

Annual, cylindric, and globe sedges were controlled > 90% with a single application of MSMA at 2.2 kg ai/ha in field studies. But this same treatment controlled fragrant and green kyllingas only 69 and 52%, respectively. Control was increased to 82 and 81%, respectively, with a repeat application. Other postemergence-applied (POST) herbicides evaluated included bentazon, halosulfuron, imazapic, imazaquin, and CGA-362622. Postemergence-applied herbicides were applied either once or twice, as well as alone and in combination with MSMA. In general, a sequential application of MSMA, either alone or in combination with any of the aforementioned herbicides, except bentazon, provided maximum control of the sedge and kyllinga species evaluated. Preemergence-applied (PRE) oxadiazon and S-metolachlor, controlled annual sedge ≥ 94% at 7 wk after treatment (WAT) in field studies and 96 and 70% at 9 WAT, respectively. Dithiopyr and prodiamine provided 86 to 80% control of annual sedge over the 9-wk rating period. In a hydroponic-type laboratory study, oxadiazon and S-metolachlor were more effective than atrazine, bensulide, imazaquin, oryzalin, or simazine, in reducing seedling development of annual, cylindric, and globe sedges, and green kyllinga. Nomenclature: Atrazine; bensulide; bentazon; CGA-362622 (proposed common name trifloxysulfuron), N-([(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl)-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; dithiopyr; halosulfuron; imazapic; imazaquin; S-metolachlor; MSMA; oryzalin; oxadiazon; prodiamine; simazine; annual sedge, Cyperus compressus L. #3 CYPCP; cylindric sedge, Cyperus retrorsus Chapm. # CYPRT; fragrant kyllinga, Kyllinga odorata Vahl. [Cyperus sesquiflorus (Torr.) Mattf. and Kuekenth.](no code); globe sedge, Cyperus globulosus Aubl. # CYPGL; green kyllinga, Kyllinga brevifolia Rottb. # KYLBR. Additional index words: CYPCP, CYPGL, CYPRT, KYLBR, turfgrass weed control. Abbreviations: POST, postemergence; PRE, preemergence; WAIT, weeks after initial treatment; WAT, weeks after treatment.

Invasion Dynamics and Genotypic Diversity of Cogongrass (Imperata cylindrica) at the Point of Introduction in the Southeastern United States

Abstract Nine sites of cogongrass were included in a study of genotypic diversity and spread dynamics at the point of introduction and its adjacent areas in the southern United States. Clones evaluated with two primer pairs yielded a total of 137 amplified fragment length polymorphism (AFLP) loci of which 102 (74.4%) were polymorphic. Genetic diversity was measured as the percentage of polymorphic, Shannons information index, Neis gene diversity, and panmictic heterozygosity. Neis gene diversity (HS) across all nine sites was estimated to be 0.11 and within site gene diversity ranged from 0.06 to 0.16. Bayesian estimate of gene diversity and Shannons information index were higher (0.17 and 0.17, respectively). The samples from the point of introduction (Pi) had the lowest genetic diversity for all types of estimates. Within site variance accounted for 56% of the total variation and among site variance 44% (P < 0.05). Differentiation among sites was assessed using FST. The greatest difference was found between the Pi and the others. No relationship was found between genetic and geographic distances. Principal component analysis as well as cluster analysis separated individuals into three main clusters. The Pi formed a separate subcluster. Gene flow (Nm), inferred from Φ-statistics describing the genetic differentiation between pairs of sites ranged from 0.6 to 5.55. The lack of significant relationship between gene flow and geographic distance as well as genetic and geographic distances suggests that the invasion dynamics of cogongrass into the southern United States is primarily through anthropogenic activities and to the lesser extent through natural forces. Nomenclature: cogongrass, Imperata cylindrica (L.) P. Beauv; Brazilian satintail, Imperata braziliensis Trin.; satintail, Imperata brevifolia Vasey; satsuma orange, Citrus reticulata L.; CTAB, cetyltrimethyl ammonium bromide; DNA, deoxyribonucleic acid.

Efficacy of Residual And Non-Residual Herbicides Used in Cotton Production Systems When Applied with Glyphosate, Glufosinate, or Msma

Field experiments were conducted to evaluate weed control provided by glyphosate, glufosinate, and MSMA applied alone or in mixture with residual and nonresidual last application (LAYBY) herbicides. Herbicide treatments included glyphosate early postemergence (EPOST) alone or followed by glyphosate, glufosinate, or MSMA late-postemergence (LPOST) alone or tank-mixed with one of the following LAYBY herbicides: carfentrazone-ethyl at 0.3 kg ai/ha, diuron at 1.12 kg ai/ha, flumioxazin at 0.07 kg ai/ha, fluometuron at 1.12 kg ai/ha, lactofen at 0.84 kg ai/ha, linuron at 0.56 kg ai/ha, oxyfluorfen at 1.12 kg ai/ha, prometryn at 1.12 kg ai/ha, or prometryn + trifloxysulfuron at 1.12 kg ai/ha + 10 g ai/ha. Residual herbicides were also applied alone LPOST. Weeds evaluated included barnyardgrass, broadleaf signalgrass, coffee senna, entireleaf morningglory, hemp sesbania, ivyleaf morningglory, johnsongrass, large crabgrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, sicklepod, smooth pigweed, spiny amaranth, and velvetleaf. Treatments containing MSMA provided lower average weed control compared to those containing glyphosate or glufosinate, and residual herbicides applied alone provided inadequate weed control compared to mixtures containing a nonresidual herbicide. Across 315 of 567 comparisons (55%), when a LAYBY herbicide was added, weed control increased. The most difficult to control weed species at all locations was pitted morningglory. Barnyardgrass and hemp sesbania at the Mississippi location and hemp sesbania at the Louisiana location were collectively difficult to control across all treatments as well. Nomenclature: carfentrazone-ethyl; diuron; flumioxazin; fluometuron; glufosinate; glyphosate; lactofen; linuron; MSMA; oxyfluorfen; prometryn; trifloxysulfuron; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash BRAPP; coffee senna, Cassia occidentalis L. CASOB; entireleaf morningglory, Ipomoea hederacea var. integruiscula Grey IPOHG; hemp sesbania, Sesbania exaltata (Raf.) Rydb.ex A. W. Hill SEBEX; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq IPOHE; johnsongrass, Sorghum halepense L. Pers. SORHA; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri L. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; prickly sida, Sida spinosa L. SIDSP; redroot pigweed, Amaranthus retroflexus L. AMARE; sicklepod, Senna obtusifolia (L.) Irwin & Barnaby CASOB; smooth pigweed, Amaranthus hybridus L. AMACH; spiny amaranth, Amaranthus spinosus L. AMASP; velvetleaf, Abutilon theophrasti Medik. ABUTH; cotton, Gossypium hirsutum L

Engineering Advantages, Challenges and Status of Grass Energy Crops

High yield with low inputs, resistance to disease, pests and drought, adaptation to a wide range of soils and climates, and biomass composition that is optimized for end use are identified as important traits for cellulosic biomass crops. Current status and future prospects for genetic improvement are reviewed for grass crops, using Miscanthus, switchgrass, sugarcane (or energy cane) and sorghum as examples. In addition, possible approaches for integrating grasses into cellulosic biomass supply systems are discussed. It is concluded that both perennial and annual grasses can play a significant role in providing cellulosic biomass for a wide range of bioenergy applications, and considerable potential exists for genetic improvement of grass crops for this purpose.

Effect of exercise and environmental terrain on development of the digital cushion and bony structures of the bovine foot.

OBJECTIVE To determine whether exercise on alternative terrain affects the development of the digital cushion and bony structures of the bovine foot. ANIMALS 20 weaned bull calves. PROCEDURES Two-month-old calves were randomly allocated to an exercise or control group. For 4 months, the control group was maintained in grass paddocks, and the exercise group was maintained in a 0.8-km lane with a mixed terrain of dirt, stones (0.32- to 0.95-cm pea gravel and 5-cm crusher run), and grass. Water and food for the exercise group were located at opposite ends of the lane; calves were fed twice daily, which ensured they walked 3.2 km/d. Pedometers were applied to all calves to measure distance traveled. All calves were slaughtered at 6 months of age. The right forefeet and hind feet were harvested for MRI and CT evaluation. RESULTS Control calves walked a mean of 1.1 km daily, whereas the exercised calves walked a mean of 3.2 km daily. Mean digital cushion volume and surface area were 25,335 mm(3) and 15,647 mm(2), respectively, for the exercised calves and 17,026 mm(3) and 12,745 mm(2), respectively, for the control calves. When weight was controlled, mean digital cushion volume and surface area for the exercise group were increased by 37.10% and 18.25%, respectively, from those for the control group. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that exercise on alternative terrain increased the volume and surface area of the digital cushion of the feet of dairy calves, which should make them less susceptible to lameness.

Effects of subsurface aeration and trinexapac-ethyl application on soil microbial communities in a creeping bentgrass putting green

Abstract. The sensitivity of creeping bentgrass (Agrostis palustris Huds.) to the extreme heat found in the southeastern United States has led to the development of new greens-management methods. The purpose of this study was to examine the effects of subsurface aeration and growth regulator applications on soil microbial communities and mycorrhizal colonization rates in a creeping bentgrass putting green. Two cultivars (Crenshaw and Penncross), a growth regulator (trinexapac-ethyl), and subsurface aeration were evaluated in cool and warm seasons. Total bacterial counts were higher in whole (unsieved) soils than in sieved soils, indicating a richer rhizosphere soil environment. Mycorrhizal infection rates were higher in trinexapac-ethyl (TE) treated plants. High levels of hyphal colonization and relatively low arbuscule and vesicle occurrence were observed. Principal components analysis of whole-soil fatty acid methyl ester (FAME) profiles indicated that warm-season microbial populations in whole and sieved soils had similar constituents, but the populations differed in the cool season. FAME profiles did not indicate that subsurface aeration and TE application affected soil microbial community structure. This is the first reported study investigating the influences of subsurface aeration and TE application on soil microorganisms in a turfgrass putting green soil.