Quantitative evolution of aggressiveness of powdery mildew under two-cultivar barley mixtures

The effects of cultivar mixtures on the evolution of aggressiveness of barley powdery mildew ( Blumeria graminis f.sp . hordei ) were modelled. It was found that the rate and direction of evolution of pathogen aggressiveness in a race-non-specific system and value at equilibrium, depends on initial resistance levels, proportions of component cultivars, autodeposition rates, the relative magnitude of the benefit of autoinfection, and the cost of alloinfection of spores. In the model, mixing cultivars in any proportions tended to reduce the aggressiveness of pathogens at equilibrium compared with pure stands, but this effect decreased when two mixture components were extremely unbalanced in proportion. Under low and medium autodeposition rates, the best control of the evolution of the pathogen was achieved by mixing two components in roughly equal proportions. The magnitude of aggressiveness at equilibrium increased as autodeposition rates increased. Though the level of initial resistance of mixture components did not have an impact on the aggressiveness of pathogens at equilibrium, it strongly influenced the transient values of aggressiveness and therefore the total amount of disease caused over an evolutionary period. The cost to the pathogen of alloinfection and benefit of autoinfection per se did not affect the final level of aggressiveness, but did affect the time to reach equilibrium. However, the ratio of the cost to the benefit did influence the final aggressiveness of the pathogen.     

The blowgun is mightier than the chainsaw in determining population density of Bornean orangutans (Pongo pygmaeus morio) in the forests of East Kalimantan

Due to its practical relevance to conservation, considerable efforts have been devoted to understanding the effects of logging on orangutan (Pongo spp.) population densities. Despite these efforts, consistent patterns have yet to emerge. We conducted orangutan nest surveys and measured forest quality and disturbance level at 108 independent locations in 22 distinct sites in the forests of the Berau and East Kutai regencies of East Kalimantan, Indonesia. Survey locations varied substantially in orangutan density, forest structure, distance to villages, and logging intensity. We incorporated site-specific nest tree composition into our estimates of nest decay rates to reduce errors associated with inter-site differences in nest tree selection. Orangutan nest densities were uncorrelated with altitude, fig density, or any other ecological measure. Multivariate analyses demonstrated that densities were not significantly affected by logging intensity (at the relatively light levels we report here) or the distance to the nearest village, but were positively correlated with the distance from the nearest village known to hunt orangutans. These results indicate that provided hunting is absent, lightly to moderately degraded forests retain high conservation value for orangutans. Widespread incorporation of degraded areas into management plans for orangutan populations would substantially increase the size of populations that could be protected, and thereby improve their changes for long-term survival.     

Interspecific hybridisation of soybeans and perennial Glycine species indigenous to Australia via embryo culture

Summary Five sterile hybrids (2n=59) between a synthetic amphiploid of Glycine tomentella (2n=38) and G. caneseens (2n=40) as female and soybean cultivars Lincoln and Hark as males have been produced by embryo or ovule culture using transplanted endosperm. The hybrid plants are twining perennials like the female parent but possess a number of morphological characters which reflect the presence of the soybean genome. Indophenol oxidase isozymes from leaf extracts also provide good evidence of the hybrid nature of the cultured plants. These hybrids open the way for the exploitation of the diverse germplasm resources of the perennial Glycine species in soybean breeding.     

Isolation of induced mutants in linseed (Linum usitatissimum) having reduced linolenic acid content

Summary Seeds of Linum usitatissimum cv. Glenelg were treated with either gamma-rays or EMS in an attempt to induce mutations with a lower level of linolenic acid in linseed oil. Two mutant lines were identified in which linolenic acid constituted approximately 29% of the total fatty acid content compared with 43% in seed oil from untreated Glenelg plants. The reduced level of linolenic acid in the mutants is accompanied by an increase in the level of linoleic acid to 30% compared with 18% in Glenelg, but there was no change in the proportions of other fatty acids. These proportions of linolenic acid and linolenic acid are respectively the highest and lowest yet reported in stable genotypes of L. usitatissimum. The strong inverse relationship between these two fatty acids in these genotypes suggests that linolenic acid is synthesised by desaturation of linolenic acid and indicates that it may be possible to breed an edible linseed oil having both low levels of linolenic acid and high levels of linolenic acid.     

Regional estimates of carbon sequestration potential: linking the Rothamsted Carbon Model to GIS databases

 Soil organic matter (SOM) represents a major pool of carbon within the biosphere. It is estimated at about 1400 Pg globally, which is roughly twice that in atmospheric CO₂. The soil can act as both a source and a sink for carbon and nutrients. Changes in agricultural land use and climate can lead to changes in the amount of carbon held in soils, thus, affecting the fluxes of CO₂ to and from the atmosphere. Some agricultural management practices will lead to a net sequestration of carbon in the soil. Regional estimates of the carbon sequestration potential of these practices are crucial if policy makers are to plan future land uses to reduce national CO₂ emissions. In Europe, carbon sequestration potential has previously been estimated using data from the Global Change and Terrestrial Ecosystems Soil Organic Matter Network (GCTE SOMNET). Linear relationships between management practices and yearly changes in soil organic carbon were developed and used to estimate changes in the total carbon stock of European soils. To refine these semi-quantitative estimates, the local soil type, meteorological conditions and land use must also be taken into account. To this end, we have modified the Rothamsted Carbon Model, so that it can be used in a predictive manner, with SOMNET data. The data is then adjusted for local conditions using Geographical Information Systems databases. In this paper, we describe how these developments can be used to estimate carbon sequestration at the regional level using a dynamic simulation model linked to spatially explicit data. Some calculations of the potential effects of afforestation on soil carbon stocks in Central Hungary provide a simple example of the system in use. Received: 1 December 1997     

Separation and characterization of a salt-dependent pectin methylesterase from Citrus sinensis var. Valencia fruit tissue

A pectin methylesterase (PME) from sweet orange fruit rag tissue, which does not destabilize citrus juice cloud, has been characterized. It is a salt-dependent PME (type II) and exhibits optimal activity between 0.1 and 0.2 M NaCl at pH 7.5. The pH optimum shifted to a more alkaline range as the salt molarity decreased (pH 8.5-9.5 at 50 mM NaCl). It has an apparent molecular mass of 32.4 kDa as determined by gel filtration chromatography, an apparent molecular mass of 33.5 kDa as determined by denaturing electrophoresis, and a pI of 10.1 and exhibits a single activity band after isoelectric focusing (IEF). It has a K(m) of 0.0487 mg/mL and a V(max) of 4.2378 nkat/mg of protein on 59% DE citrus pectin. Deblocking the N-terminus revealed a partial peptide composed of SVTPNV. De-esterification of non-calcium-sensitive pectin by 6.5% increased the calcium-sensitive pectin ratio (CSPR) from 0.045 +/- 0.011 to 0.829 +/- 0.033 but had little, if any, effect on pectin molecular weight. These properties indicate this enzyme will be useful for studying the PME mode of action as it relates to juice cloud destabilization.     

A high-throughput method for the quantification of proanthocyanidins in forage crops and its application in assessing variation in condensed tannin content in breeding programmes for Lotus corniculatus and Lotus uliginosus

Lotus corniculatus and Lotus uliginosus are agronomically important forage crops used in ruminant livestock production. The condensed tannin (CT) content, dry matter (DM) production, and persistence of these species are key characteristics of interest for future exploitation of these crops. Here we present field data on 19 varieties of L. corniculatus, 2 varieties of L. uliginosus and, additionally, a glasshouse experiment using 6 varieties of L. corniculatus and 2 varieties of L. uliginosus. Current methods for the quantification of condensed tannins in crop species are slow and labor intensive and are generally based upon polymer hydrolysis following the extraction of chlorophyll in a liquid phase. Presented here is a high-throughput protocol for condensed tannin quantification suitable for microtiter plates based upon the precipitation of condensed tannin polymers in complex with bovine serum albumin (BSA) with subsequent hydrolysis of precipates using butan 1-ol/ hydrochloric acid.     

Fluvial development and the sediment regime of the lower Calder,Ribble catchment,northwest England

In the lower reaches of the Calder (Lancashire) tributary of the Ribble catchment (northwest England), five river terraces set into the surrounding glacial terrain have been mapped and their underlying sediments radiocarbon dated. The earliest terrace (T1) reflects sandur-style deposition during deglaciation and it aggraded in a reach cut into glacial diamict and glaciolacustrine muds. Incision below T1 spanned the start of the Holocene, driven by a combination of reduced sediment supply under a stabilising landscape and lower base-levels. T2 had aggraded and was being abandoned by 4000 BC; its formation latterly involving a period of comparative stability in terms of channel migration, perhaps a function of extensive forest cover and sea levels reaching above present day levels. The last 3000 years were marked by substantial changes in the sedimentary regime, with increased and varying sediment supply driving cycles of cut-and-fill and greater lateral channel migration. These changes coincided with the first widespread and substantial reductions in forest cover and a progression towards an agricultural landscape. Between the aggradation of terraces T3 and T4 there was a substantial increase in sediment supply, which is broadly in keeping with the erosion history in the surrounding uplands. This sediment slug appears to have induced a switch from highly sinuous meandering to lower sinuosity channels characterised by lateral scroll-style migration. Late Holocene vegetation changes, particularly woodland removal, driven by anthropogenic land-pressure appear to have rendered the floodplain prone to channel migration and the landscape more susceptible to erosion.