Population structure of the rice sheath blight pathogen <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> AG-1 IA from India

The population structure of Rhizoctonia solani AG-1 IA causing rice sheath blight from India was evaluated for 96 isolates using seven RFLP loci. Nineteen of the isolates did not hybridise to R. solani AG-1 IA RFLP probes and rDNA analyses subsequently confirmed that they were either Ceratobasidium oryzae-sativae isolates or another Rhizoctonia sp. The population structure of the remaining 77 R. solani AG-1 IA Indian isolates was similar to that of a previously characterized Texas population. Clonal dispersal of R. solani AG-1 IA in India was moderate within fields and no clones were shared among field populations. Low levels of population subdivision and small genetic distances among populations were consistent with high levels of gene flow. Frequent sexual reproduction was indicated by the fact that most populations were in Hardy–Weinberg equilibrium (HWE). The two loci (R68 and R111) that deviated significantly from HWE showed an excess of heterozygosity. Although Texas and Indian populations were geographically very distant, they exhibited only moderate population subdivision, with an F_ST value of 0.193.     

Using the CERES-Maize model in a semi-arid Mediterranean environment. Evaluation of model performance

The CERES-Maize model was tested in a semi-arid Mediterranean environment during a period of 2 years under three different soil moisture conditions (well-watered and two limited irrigation regimes). In well-watered plots, growth and yield were adequately simulated by the model (differences between simulated values and observations were less than 10%). Results suggest that the absence of air humidity among the model inputs does not limit the CERES-Maize performance, even under dry-air conditions. On the contrary, under mild soil water shortage, CERES-Maize underestimated the leaf area index (LAI) (up to 26% for maximum LAI), above-ground biomass (up to 23%) and grain yield (up to 15%). Mismatches between observations and predictions increased with water stress level (by up to 46, 29 and 23% for maximum LAI, biomass and grain yield, respectively). It is suggested that the functions describing leaf growth and senescence and those calculating the soil water deficit functions should be modified to adapt CERES-Maize to Mediterranean environments.     

Evaluation of dietary addition of 2 essential oils from Achillea moschata,or their components (bornyl acetate,camphor, and eucalyptol) on in vitro ruminal fermentation and microbial community composition

This study investigated the effects of 2 Achillea moschata essential oils extracted from plants collected in 2 different valleys of the Italian Alps and 3 pure compounds of oils — bornyl acetate (BOR), camphor (CAM), and eucalyptol (EUCA) — on in vitro ruminal fermentation and microbiota. An in vitro batch fermentation experiment (Exp. 1) tested the addition of all of the substances (2 essential oils and 3 compounds) in fermentation bottles (120 mL) at 48 h of incubation, whereas a subsequent in vitro continuous culture experiment (Exp. 2) evaluated the pure compounds added to the fermenters (2 L) for a longer incubation period (9 d). In both experiments, total mixed rations were incubated with the additives, and samples without additives were included as the control (CTR). Each treatment was tested in duplicate and was repeated in 3 and 2 fermentation runs in Exp. 1 and 2, respectively. Gas production (GP) in Exp. 1 was similar for all of the treatments, and short chain volatile fatty acid (SCFA) production was similar in both experiments except for a decrease of SCFA produced (P = 0.029) due to EUCA addition in Exp. 2. Compared to CTR, BOR and CAM reduced the valerate proportion (P = 0.04) in Exp. 1, and increased (P < 0.01) the acetate proportion in Exp. 2. All treatments increased (P < 0.01) total protozoa counts (+36.7% and +48.4% compared to CTR on average for Exp. 1 and 2, respectively). In Exp. 1, all of the treatments lowered the Bacteroidetes and Firmicutes and increased the Proteobacteria relative abundances (P < 0.05), whereas in Exp. 2, the EUCA addition increased (P = 0.012) the Ruminococcus. In Exp. 1, methane (CH₄) as a proportion of the GP was lowered (P = 0.004) by the addition of CAM and EUCA compared to CTR, whereas in Exp. 2, EUCA reduced the amount of stoichiometrically calculated CH₄ compared to CTR. Overall, essential oils extracted from A. moschata and the pure compounds did not depress in vitro rumen fermentation, except for EUCA in Exp. 2. In both experiments, an increase of the protozoal population occurred for all the additives.     

SOILPAR 2.00: software to estimate soil hydrological parameters and functions

2 is a program for estimating soil parameters. It allows: (1) storing soil data in a georeferenced database, (2) computing estimates of soil hydrological parameters using 15 procedures, (3) comparing the estimates against measured data using both statistical indices and graphics, and (4) creating maps using the ESRI format. An interface to/from Excel and CropSyst is provided. Eleven methods estimate one or more of the following characteristics: soil water content at predefined soil matrix tension, saturated hydraulic conductivity, and bulk density. Three methods estimate the parameters of well-known soil water retention functions (Brooks-Corey, Hutson-Cass, van Genuchten), and one estimates both saturated soil hydraulic conductivity and the soil water retention curve parameters (Campbell). The software runs under Windows 98/NT/2000/XP and is freely downloadable via internet.     

Physiological complexity and plant genetic manipulation

Summary One of the limiting factors in the development of new cultivars in a reasonable time using recombinant DNA techniques, is an inability to predict the interaction between the introgressed gene(s) and the host genome and metabolism.This review presents a survey of the literature on the constraints determining the coherence between alien sequences and their products, and the organization of the receiving genome and its physiological equilibrium. An hypothesis supported by preliminary experimental data is put forward that such constraints derive from coadaptation during the evolution of gene complexes driven by external selection pressure, and by changes in genes coding for key factors of plant metabolism. Conclusions are finally drawn on a series of possible methods to be used in genetic engineering, in relation to breeding practice, compatible with the rules governing the organization of physiological networks.     

CropSyst, a cropping systems simulation model

CropSyst is a multi-year, multi-crop, daily time step cropping systems simulation model developed to serve as an analytical tool to study the effect of climate, soils, and management on cropping systems productivity and the environment. CropSyst simulates the soil water and nitrogen budgets, crop growth and development, crop yield, residue production and decomposition, soil erosion by water, and salinity. The development of CropSyst started in the early 1990s, evolving to a suite of programs including a cropping systems simulator (CropSyst), a weather generator (ClimGen), GIS-CropSyst cooperator program (ArcCS), a watershed model (CropSyst Watershed), and several miscellaneous utility programs. CropSyst and associated programs can be downloaded free of charge over the Internet. One key feature of CropSyst is the implementation of a generic crop simulator that enables the simulation of both yearly and multi-year crops and crop rotations via a single set of parameters. Simulations can last a fraction of a year to hundreds of years. The model has been evaluated in many world locations by comparing model estimates to data collected in field experiments. CropSyst has been applied to perform risk and economic analyses of scenarios involving different cropping systems, management options, and soil and climatic conditions. An extensive list of references related to model development, evaluation, and application is provided.     

Investigation of Nitrification and Denitrification in the Sediment of Wastewater Stabilization Ponds

Kinetic studies of nitrification and denitrification were carried out on reconstituted cores of sediments taken from wastewater stabilization ponds. This study aims to quantify the nitrification and denitrification in the sediment and to offer kinetic models to describe the processes. Sediment cores were collected, and laboratory studies were performed. The result showed that nitrification and denitrification processes are absent in the water column of stabilization ponds of the Bertrix (Belgium) wastewater treatment plant. On the contrary, nitrification and denitrification rates measured on 18 cores of sediment are, respectively, in the range of 0.12?C1.56 g N-NH ₄ ⁺ /m² day and 0.1?C1.2 g N/m² day. In order to describe nitrification and denitrification processes, two kinetic models were developed using the Monod standard equation.