Tami L. Stubbs

Host range of a deleterious rhizobacterium for biological control of downy brome

Abstract Pseudomonas fluorescens strain D7 (P. f. D7; NRRL B-18293) is a root-colonizing bacterium that inhibits downy brome (Bromus tectorum L. BROTE) growth. Before commercialization as a biological control agent, strain D7 must be tested for host plant specificity. Agar plate bioassays in the laboratory and plant–soil bioassays in a growth chamber were used to determine the influence of P. f. D7 on germination and root growth of 42 selected weed, cultivated or native plant species common in the western and midwestern United States. In the agar plate bioassay, all accessions of downy brome were inhibited by P. f. D7. Root growth of seven Bromus spp. was inhibited an average of 87% compared with that of controls in the agar plate bioassay. Root growth of non-Bromus monocots was reduced by 0 to 86%, and only 6 out of 17 plant species were inhibited 40% or greater. Among all plant species, only downy brome root growth from two accessions was significantly inhibited by P. f. D7 in plant–soil bioassays (42 and 64%). P. f. D7 inhibited root growth and germination in agar plate bioassays more than in plant–soil bioassays. Inhibition in plant–soil bioassays was limited to downy brome, indicating promise for P. f. D7 as a biocontrol agent that will not harm nontarget species. Nomenclature: Downy brome; Bromus tectorum L. BROTE; rhizobacterium; Pseudomonas fluorescens.

Soil Ecosystem Changes During the Transition to No-Till Cropping

Summary Growers in the United States and worldwide are adopting no-tillage (no-till) cropping to reduce soil erosion, improve soil quality, increase water infiltration, and reduce number of passes with farm equipment over their fields. Soil erosion from dry farmed (i.e., non-irrigated) cropland in most regions of the United States exceeds the tolerable rate. An understanding of the changes in the soil ecosystem with changing tillage practices is needed to minimize the impact of agriculture on the environment and foster the use of sustainable agricultural practices. The soil biota is critical to the functioning of any agro-ecosystem, but studying the soil biota is difficult due to the diversity and the challenges associated with isolating and identifying these organisms. Soil disturbance or lack of disturbance can have a profound effect on biotic populations, processes and community structure. This contribution examines changes that occur in soil during the transition to no-till cropping, interrelations among organisms in the soil food web, and the relationships between organisms and their environment. As interest grows in sustainable cropping systems that mimic processes and soil organic matter turnover of native, undisturbed systems, it is imperative to understand how the transition to no-till affects an organisms niche, or functional role within the soil environment. Ecosystem investigations will enhance the understanding of changes that occur with the adoption of reduced tillage and no-till cropping systems so that these systems become increasingly viable.

Nitrogen contribution of rye–hairy vetch cover crop mixtures to organically grown sweet corn

Organic cropping systems that utilize winter grown cereal–legume cover crop mixtures can increase plant available nitrogen (N) to a subsequent cash crop, but the rate of N release is uncertain due to variations in residue composition and environmental conditions. A study was conducted to evaluate N availability from rye ( Secale cereale L.)–hairy vetch ( Vicia villosa Roth) cover crop mixtures and to measure the response of organically grown sweet corn ( Zea mays L.) to N provided by cover crop mixtures. Nitrogen availability from pure rye, pure hairy vetch, and rye–vetch mixtures was estimated using laboratory incubation with controlled temperature and soil moisture. Sweet corn N response was determined in a 2-year field experiment in western Washington with three cover crop treatments as main plots (50:50 rye–vetch seed mixture planted mid September, planted early October, and none) and four feather meal N rates as subplots (0, 56, 112 and 168 kg available N ha −1 ). Pure hairy vetch and a 75% rye–25% hairy vetch biomass mixture (R 75 V 25 ) released similar amounts of N over 70 days in the laboratory incubation. But, the initial release of N from the (R 75 V 25 ) treatment was nearly 70% lower, which may result in N release that is better timed with crop uptake. Cover crops in the field were dominated by rye and contained 34–76 kg ha −1 total N with C:N ranging from 18 to 27. Although time of planting and management of cover crop quality improved N uptake in sweet corn, cover crops provided only supplemental plant available N in this system.

Using NIRS to predict fiber and nutrient content of dryland cereal cultivars.

Residue from cultivars of spring wheat (Triticum aestivum L.), winter wheat, and spring barley (Hordeum vulgare L.) was characterized for fiber and nutrient traits using reference methods and near-infrared spectroscopy (NIRS). Calibration models were developed for neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), carbon (C), sulfur (S), nitrogen (N), and C:N. When calibrations were tested against validation sets for each crop year, NIRS was an acceptable method for predicting NDF (standard error of prediction (SEP)<0.87; R2>0.90) and ADF (SEP< 0.81; R2>0.92) and moderately successful for ADL in 1 year of the study (SEP=0.44; R2=0.81) but less successful for C, S, N, and C:N (R2 all<0.57). These results indicate that NIRS can predict the NDF and ADF of cereal residue from dryland cropping systems and is a useful tool to estimate residue decomposition potential.

Microbial Weed Control and Microbial Herbicides

Microbial weed control represents an innovative means to manage troublesome weeds and utilize the naturally occurring biological herbicides produced by soil microorganisms. These compounds kill or hinder the growth of weeds so that beneficial plant species can gain a competitive advantage. The vast diversity of microorganisms in our environment is largely untapped, and the potential discovery and characterization of these microbial compounds represents an opportunity to complement chemical herbicides, or reduce the potential for erosion or soil degradation due to tillage for weed control. Invasive weeds continue to threaten the productivity of agricultural lands and natural areas; however, for many weeds adequate, cost-effective control measures presently are not available (Jones & Sforza, 2007). Discovery of biological controls for invasive plants represents an alternative way to slow the spread of these weeds using natural enemies (Jones & Sforza, 2007). Further advances in microbial genetics will continue to improve our understanding of the wealth of genetic diversity and potential in the soil and to better use plant-microbe interactions. The development of biocontrol agents would lessen the need for chemical herbicides and provide greater options for weed management. Microbes have a place in integrated, ecologically based weed management and their potential is only just being realized.

An assessment of environmental conditions for control of downy brome by Pseudomonas fluorescens D7

Purpose: We evaluated the conditions that favoured Pseudomonas fluorescens strain D7 (P.f. D7) growth and inhibition of downy brome. Design/methodology/approach: Tn5 mutagenesis and a competitive assay were used to isolate mutants of P.f. D7. Isolates were screened for polysaccharide production and toxin response. Seven mutants were tested under varying pH, temperature and water potential and characterised using Random Amplified Polymorphic DNA analysis. Findings: Temperature, pH, and water potential did not affect weed suppression in bioassays, except at 37°C and with NaCl. Originality and/value: Understanding the genetics of P.f. D7 will help in the development of successful weed biocontrol systems.

Survival of a Rifampicin-Resistant Pseudomonas fluorescens Strain in Nine Mollisols

Pseudomonas fluorescens strain D7 (P.f. D7) is a naturally occurring soil bacterium that shows promise as a biological herbicide to inhibit growth of annual grass weeds, including downy brome (Bromus tectorum L.), in crop- and rangelands. Pseudomonas fluorescens strain D7rif (P.f. D7rif) is a rifampicin-resistant strain of P.f. D7. One of the greatest obstacles to successful biological weed control is survival of the organism under field conditions. Nine soils in the taxonomic order of Mollisols, collected from downy brome-infested areas of the Western and Central United States, were inoculated with P.f. D7rif and incubated in the laboratory to determine the effects of soil type, soil properties, incubation temperature, and soil water potential on survival of P.f. D7rif over 63 days. Silt loam soils from Lind, Washington, and Moro, Oregon, sustained the highest P.f. D7rif populations, and recovery was the lowest from Pendleton, Oregon soil. Survival and recovery of P.f. D7rif varied with soil type and temperature but not with the two soil water potentials tested. After 63 days, P.f. D7rif was recovered at levels greater than log 5.5 colony forming units (CFU) g−1 soil from five of the nine test soils, a level adequate to suppress downy brome under field or range conditions.

Soil Quality and Conservation Tillage in the Palouse and Dryland Farming Regions of the Pacific Northwest

Include a problem statement, objectives, brief methods, quantitative results, and the significance of your findings. The abstract should be no more than 250 words long. Soil quality was assessed at several long-term dryland cropping systems research sites in eastern Washington and northern Idaho to further define management practices that build rather than degrade soil. The objective was to characterize soil quality changes over time as affected by tillage and cropping system at sites near Colfax, Ritzville, and Lind, WA and Genesee, ID. We found that soil quality changes during the transition from tillage-based farming to no-till are less dramatic and more variable in the low precipitation (150– to 300– mm annual) zone compared to the higher precipitation (300– to 550– mm annual) zone. Tillage impacts soil quality more than surface residue management or crop rotation. Soil organic carbon (SOC) slowly increased in long-term no-till and approached or exceeded that of nearby undisturbed native soil. Long-term no-till also increased the proportion of aggregates in the larger sized soil fractions. We also see that long-term no-till results in microbial community changes and an increase in the fungal:bacterial ratio. Data from these longterm experiments will allow us to better assess the productivity and quality of soils in the Palouse and other dryland cropping regions of the Inland Pacific Northwest. This information will allow identification of soil quality parameters that can be used in the development of best management practices for conserving soil quality and enhancing crop production.

Investigating Soil Microorganisms for Biological Weed Control.

Ask a student to give an example of an ecosystem and the response is predictable-the rainforest, the grasslands-typical examples from a biology text. Some adventurous soul might suggest a local example, but it would be a rare student who would volunteer soil as an example. Except for soil scientists, most of us ignore soil. We seldom consider the dependence of our agricultural systems and our world food supply on fertile soil. The soil is more than just an inert plant growth medium-it is teeming with life. A pinch of soil contains billions of tiny organisms critical to the functioning of soil (Wood 1989). Healthy soil, full of active microorganisms in correct balance, is essential to plant growth. Soil is home to large numbers of many different types of microorganisms assembled in complex and diverse communities, each sensitive to specific stimulations and stresses. What are the biological components of soil? What living organisms are part of this ecosystem, and how many are present? How are the number and variety of these organisms altered by human activities such as farming or gardening? Does the use of herbicides, fertilizers and pesticides or the presence of pollution influence these organisms? Soil provides a readily available example of an ecosystem and one small

Prediction of Canola Residue Characteristics Using Near-Infrared Spectroscopy

Little work has been done to characterize and quantify the residue traits affecting decomposition of winter and spring canola (Brassica napus L.) residue in dryland farming systems of the Pacific Northwest United States. Traditional methods of characterizing residue fiber and nutrients are time-consuming and expensive and require large quantities of chemical reagents. The goal of this research was to determine whether near-infrared spectroscopy (NIRS) could accurately predict neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), carbon (C), and nitrogen (N) of canola stems, litter, and roots and decomposition of canola stems. Canola residue varied in decomposition, fiber, and nutrients by year, location, and type. NIRS predictions were successful for NDF and ADF in 2011 (standard error of prediction ; ) and NDF, ADF, and N in 2012 ( ; ). Other predictions for residue fiber and nutrient characteristics were considered moderately successful. Prediction of canola residue decomposition with NIRS was useful for screening purposes. Near-infrared spectroscopy shows promise for rapidly and reproducibly predicting some canola residue fiber and nutrient traits and may be useful for estimating residue decomposition potential in dryland conservation cropping systems.