Active remote sensing and grain yield in irrigated maize

Advances in agricultural technology have led to the development of active remote sensing equipment that can potentially optimize N fertilizer inputs. The objective of this study was to evaluate a hand-held active remote sensing instrument to estimate yield potential in irrigated maize. This study was done over two consecutive years on two irrigated maize fields in eastern Colorado. At the six- to eight-leaf crop growth stage, the GreenSeeker? active remote sensing unit was used to measure red and NIR reflectance of the crop canopy. Soil samples were taken before side-dressing from the plots at the time of sensing to determine nitrate concentration. Normalized difference vegetation index (NDVI) was calculated from the reflectance data and then divided by the number of days from planting to sensing, where growing degrees were greater than zero. An NDVI-ratio was calculated as the ratio of the reflectance of an area of interest to that of an N-rich portion of the field. Regression analysis was used to model grain yield. Grain yields ranged from 5 to 24 Mg ha^?1. The coefficient of determination ranged from 0.10 to 0.76. The data for both fields in year 1 were modeled and cross-validated using data from both fields for year 2. The coefficient of determination of the best fitting model for year 1 was 0.54. The NDVI-ratio had a significant relationship with observed grain yield (r ² = 0.65). This study shows that the GreenSeeker? active sensor has the potential to estimate grain yield in irrigated maize; however, improvements need to be made.     

Effect of farm management on topsoil organic carbon and aggregate stability in water: A case study from Southwest England,UK

There are few reliable data sets to inspire confidence in policymakers that soil organic carbon (SOC) can be measured on farms. We worked with farmers in the Tamar Valley region of southwest England to select sampling sites under similar conditions (soil type, aspect and slope) and management types. Topsoils (2–15 cm) were sampled in autumn 2015, and percentage soil organic matter (%SOM) was determined by loss on ignition and used to calculate %SOC. We also used the stability of macroaggregates in cold water (WSA) (‘soil slaking’) as a measure of ‘soil health’ and investigated its relationship with SOC in the clay‐rich soils. %SOM was significantly different between management types in the order woodland (11.1%) = permanent pasture (9.5%) > ley‐arable rotation (7.7%) = arable (7.3%). This related directly to SOC stocks that were larger in fields under permanent pasture and woodland compared with those under arable or ley‐arable rotation whether corrected for clay content (F = 8.500, p < .0001) or not (F = 8.516, p < .0001). WSA scores were strongly correlated with SOC content whether corrected for clay content (SOC_adj R² = .571, p < .0001) or not (SOC_unadj R² = 0.490, p = .002). Time since tillage controlled SOC stocks and WSA scores, accounting for 75.5% and 51.3% of the total variation, respectively. We conclude that (1) SOC can be reliably measured in farmed soils using accepted protocols and related to land management and (2) WSA scores can be rapidly measured in clay soils and related to SOC stocks and soil management.     

Susceptibility of European bread and durum wheat cultivars to Tilletia indica

Representative European wheat cultivars were tested under quarantine containment for their susceptibility to Tilletia indica, the cause of Karnal bunt of wheat. Fifteen winter and 15 spring wheat ( Triticum aestivum ) and 11 durum wheat ( Triticum durum ) cultivars were inoculated by boot injection just prior to ear emergence to test their physiological susceptibility. Selected cultivars were then re-tested by spray inoculation after ear emergence to determine their morphological susceptibility, which is a better predictor of field susceptibility. At maturity, the ears and seeds were assessed for incidence and severity of disease. For the physiological susceptibility tests, 13/15 winter wheat cultivars were infected and the percentage of infected seeds ranged from 1 to 32%. For spring cultivars, 13/15 cultivars were infected and the percentage of infected seeds ranged from 1 to 48%. For the durum cultivars, 9/11 were infected and the percentage of infected seeds ranged from 2 to 95%. Across all cultivars, 35/41 were infected. Based on historical Karnal bunt susceptibility categories using coefficients of infection, one cultivar was classed as highly susceptible, three as susceptible, 11 as moderately susceptible, 20 as resistant and only six as highly resistant. The spray-inoculation morphological susceptibility tests broadly confirmed the physiological susceptibility results, although lower levels of infection were observed. Overall, the range of susceptibility was similar to that found in cultivars grown in Karnal bunt affected countries. The results demonstrate that European wheat cultivars are susceptible to T. indica and thus could potentially support the establishment of T. indica if introduced into Europe.     

Development of a One-Step Real-Time Polymerase Chain Reaction Assay for Diagnosis of Phytophthora ramorum

ABSTRACT Phytophthora ramorum is a recently described pathogen causing bleeding cankers, dieback, and leaf blight on trees and shrubs in parts of Europe and North America, where the disease is commonly known as sudden oak death. This article describes the development of a single-round real-time polymerase chain reaction (PCR) assay based on TaqMan chemistry, designed within the internal transcribed spacer 1 region of the nuclear ribosomal (nr)RNA gene for detection of P. ramorum in plant material. Unlike previously described methods for the molecular detection of P. ramorum, this assay involves no post amplification steps or multiple rounds of PCR. The assay was found to have a limit of detection of 10 pg of P. ramorum DNA, and could detect P. ramorum in plant material containing 1% infected material by weight within 36 cycles of PCR. The assay also was used to test DNA from 28 other Phytophthora spp. to establish its specificity for P. ramorum. A quick and simple method was used to extract DNA directly from host plant material, and detection of P. ramorum was carried out in multiplex with an assay for a gene from the host plant in order to demonstrate whether amplifiable DNA had been extracted. Amplifiable DNA was extracted from 84.4% of samples, as demonstrated by amplification of host plant DNA. The real-time protocol was used to test 320 plant samples (from 19 different plant species) from which DNA extraction had been successful, and was shown to give results comparable with a traditional isolation technique for diagnosis of P. ramorum in plant material from common U.K. hosts.     

The influence of environment on development of the mucosal immune system

The mucosal immune system expresses active responses against pathogens and also tolerance against harmless food and commensal bacterial antigens. The mechanisms that determine which of these outcomes occur after recognition of antigens by T-cells are not clear. One possibility is that it is determined by the initial interaction between a dendritic and a na?ve T-cell in organised lymphoid tissue. However, such organised structures are, evolutionarily, quite recent and the original immune system must have made appropriate responses in more diffuse immunological architecture; a second possibility is that the critical interaction is between primed T-cells and their environment, in the lamina propria of the intestine. The mucosal immune system of neonates is poorly developed and inefficient at expressing appropriate immune responses. Development is influenced by a range of environmental factors including maternally derived antigen or antibody and commensal flora and pathogens. The intestine is a complex immunological structure in which the immune system and the macro- and microenvironment interact.     

Image analysis for the identification of the quarantine pest Tilletia indica*

Diagnosis of the teliospores of Tilletia indica (Karnal bunt) detected in wash tests is complicated by the fact that wheat grain can be contaminated by ‘look‐alike’ species, namely Tilletia walkeri (ryegrass bunt) and Tilletia horrida (rice smut). Although morphological diagnosis is possible when there are relatively large numbers of teliospores present, it is difficult with only a few spores as there are significant overlaps in the characteristics of each species. Molecular methods can confirm presumptive identifications, but these take 2–3 weeks. Image analysis offers the potential for more rapid confirmation. An image analysis system was developed for use on bleached spores. Bleaching spores reveals additional morphological characters (spore profile and spore wall layers) that may be used in an image analysis system to discriminate species. The image‐processing software automatically locates spores on a given image and calculates perimeter, surface area, number of spines and spine size, maximum and minimum ray radius, aspect ratio and roundness. Principal components analysis (PCA) is performed on the parameters to obtain a linear separation of spore species. Accuracy of 97% in separating T. indica and T. walkeri has been achieved in preliminary tests using PCA, but further evaluation is required.