Enhanced degradation of atrazine under field conditions correlates with a loss of weed control in the glasshouse

Enhanced degradation of atrazine has been reported in the literature, indicating the potential for reduced residual weed control with this herbicide. Experiments were conducted to determine the field dissipation of atrazine in three cropping systems: continuous Zea mays L. (CC) receiving atrazine applications each year, Gossypium hirsutum L.-Z. mays rotation (CCR) receiving applications of atrazine once every 2 years and a no atrazine history soil (NAH). Subsequent laboratory and greenhouse experiments were conducted with soil collected from these cropping systems to determine atrazine degradation, mineralization and residual weed control. Field dissipation of atrazine followed first-order kinetics, and calculated half-life values for atrazine combined over 2003 and 2005 increased in the order of CC (9 d) = CCR (10 d) < NAH (17 d). Greenhouse studies confirmed that the persistence of atrazine was approximately twofold greater in NAH soil than in CC or CCR soil. Biometer flask mineralization studies suggested that enhanced degradation of atrazine was due to rapid catabolism of the s-triazine ring. Glasshouse efficacy studies revealed a loss of residual weed control in CC and CCR soil compared with NAH soil. These data indicate that, under typical Mississippi Delta field conditions and agronomic practices, the persistence of atrazine may be reduced by at least 50% if the herbicide is applied more than once every 24 months. Glasshouse studies suggest that under these conditions a loss of residual weed control is possible.     

A real-time PCR assay for detection and quantification of Verticillium dahliae in spinach seed

Verticillium dahliae is a soilborne fungus that causes Verticillium wilt on multiple crops in central coastal California. Although spinach crops grown in this region for fresh and processing commercial production do not display Verticillium wilt symptoms, spinach seeds produced in the United States or Europe are commonly infected with V. dahliae. Planting of the infected seed increases the soil inoculum density and may introduce exotic strains that contribute to Verticillium wilt epidemics on lettuce and other crops grown in rotation with spinach. A sensitive, rapid, and reliable method for quantification of V. dahliae in spinach seed may help identify highly infected lots, curtail their planting, and minimize the spread of exotic strains via spinach seed. In this study, a quantitative real-time polymerase chain reaction (qPCR) assay was optimized and employed for detection and quantification of V. dahliae in spinach germplasm and 15 commercial spinach seed lots. The assay used a previously reported V. dahliae-specific primer pair (VertBt-F and VertBt-R) and an analytical mill for grinding tough spinach seed for DNA extraction. The assay enabled reliable quantification of V. dahliae in spinach seed, with a sensitivity limit of ≈1 infected seed per 100 (1.3% infection in a seed lot). The quantification was highly reproducible between replicate samples of a seed lot and in different real-time PCR instruments. When tested on commercial seed lots, a pathogen DNA content corresponding to a quantification cycle value of ≥31 corresponded with a percent seed infection of ≤1.3%. The assay is useful in qualitatively assessing seed lots for V. dahliae infection levels, and the results of the assay can be helpful to guide decisions on whether to apply seed treatments.     

The internet-based fungal pathogen database: a proposed model

ABSTRACT A better understanding of the phenotypic and genetic diversity of significant agricultural pathogens and how their populations change in the field is critical for designing successful, long-term disease management strategies. Although efforts to determine the genetic diversity of plant pathogens have substantially increased in recent years, mainly due to the availability of various molecular tools, complementary efforts to archive and integrate the resulting data have been very limited. As a consequence, it is often difficult to compare the available data from various laboratories because the data have been generated by diverse tools, often preventing any direct comparisons, and are saved in a format that is unsuitable for comparative studies. The establishment of an internet-based database that cross-links the digitized genotypic and phenotypic information of individual pathogens at both the species and population levels may allow us to effectively address these problems by coordinating the generation of data and its subsequent archiving. We discuss the needs, benefits, and potential structure of such a database.     

Comparative analysis of multi-criteria probabilistic FR and AHP models for forest fire risk(FFR) mapping in Melghat Tiger Reserve(MTR) forest

A comparative study of Frequency Ratio(FR)and Analytic Hierarchy Process(AHP)models are performed for forest fire risk(FFR)mapping in Melghat Tiger Reserve forest,central India.Identification of FFR depends on various hydrometeorological parameters altitude,slope,aspect,topographic position index,normalized differential vegetation index,rainfall,air temperature,land surface temperature,wind speed,distance to settlements,and distance by road are integrated using a GIS platform.The results from FR and AHP show similar trends.The FR model was significantly higher accurate(overall accuracy of 81.3%,kappa statistic 0.78)than the AHP model(overall accuracy 79.3%,kappa statistic 0.75).The FR model total forest fire risk areas were classified into five classes:very low(7.1%),low(22.2%),moderate(32.3%),high(26.9%),and very high(11.5%).The AHP fire risk classes were very low(6.7%),low(21.7%),moderate(34.0%),high(26.7%),and very high(10.9%).Sensitivity analyses were performed for AHP and FR models.The results of the two different models are compared and justified concerning the forest fire sample points(Forest Survey of India)and burn images(2010-2016).These results help in designing more effective fire management plans to improve the allocation of resources across a landscape framework.     

Calibration and performance of moisture sensors in soilless substrates: ECH2O and Theta probes

Reliable and affordable moisture sensors for measuring the water content in soilless substrates are limited. In this study, we examined the efficacy of two moisture sensors (ECH₂O-10 and Theta probe ML2X) for measuring water content in soilless substrates. We developed calibration equations and analyzed the effect of increasing electrical conductivity (EC) and substrate temperature on the voltage output of probes. We found that a single equation (one for each probe) could be used to adequately measure water content in different custom-made substrates maintained at low EC and a substrate temperature of ∼23 °C. The calibration equation developed for the Theta probe from substrates maintained at low EC could also be used in two commercial substrates with high EC (2.0–5.0 dS m⁻¹). Further measurements in substrates maintained at different water contents and EC levels indicated that the output of the ECH₂O-10 probe, but not the Theta probe, was significantly affected by substrate EC. The lack of a substrate EC effect on the Theta probe readings was surprising, because the probe was sensitive to EC when fertilizer solutions with different ECs were measured. Increasing the temperature of the substrate from 10 to 40 °C increased the voltage output of ECH₂O-10 probes by 1.88 mV °C⁻¹, or on average 0.0022 m³ m⁻³ water content per °C. There was no effect of increasing substrate temperature on the Theta probe. It was concluded that ECH₂O-10 probes can be used in greenhouse operations requiring less measurement precision (like irrigation), however for accurate measurements of water content, the Theta probe is preferred.     

Architecture of a charge-transfer state regulating light harvesting in a plant antenna protein

Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). We found evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a delocalized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can "tune" the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophyll-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.     

HCV persistence and immune evasion in the absence of memory T cell help

Spontaneous resolution of hepatitis C virus (HCV) infection in humans usually affords long-term immunity to persistent viremia and associated liver diseases. Here, we report that memory CD4+ Tcells are essential for this protection. Antibody-mediated depletion of CD4+ Tcells before reinfection of two immune chimpanzees resulted in persistent, low-level viremia despite functional intra-hepatic memory CD8+ Tcell responses. Incomplete control of HCV replication by memory CD8+ Tcells in the absence of adequate CD4+ Tcell help was associated with emergence of viral escape mutations in class I major histocompatibility complex-restricted epitopes and failure to resolve HCV infection.     

Penetration of human-induced warming into the world's oceans

A warming signal has penetrated into the world's oceans over the past 40 years. The signal is complex, with a vertical structure that varies widely by ocean; it cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models. We conclude that it is of human origin, a conclusion robust to observational sampling and model differences. Changes in advection combine with surface forcing to give the overall warming pattern. The implications of this study suggest that society needs to seriously consider model predictions of future climate change.