Showing papers by "Adrian C. Newton published in 1998"

The Silviculture of Mahogany

Abstract: Description of the species mahogany as a plantation species seed production nursery techniques site selection plantation establishment plantation maintenance growth and yield timber quality shoot borer control protection silvicultural systems.

Diversity of ectomycorrhizal fungi in Britain: a test of the species-area relationship, and the role of host specificity

Abstract: The host range of ectomycorrhizal (ECM) fungi in Britain was examined by compilation of a data matrix from published literature sources, based primarily on accounts of sporocarp associations with particular host genera. Information was gathered for 577 species of ECM fungi belonging to 51 genera, and 25 genera of host trees, representing the majority of ECM fungal species and host genera recorded in Britain. Pronounced variation was recorded in the number of ECM fungal species associated with different host genera, with over 200 species recorded with Betula, Fagus, Pinus and Quercus. There was a positive linear relationship (r2=0·47, P=0·007) between the number of species of ECM fungi associated with different host genera and the total area occupied by each tree genus in Britain (both values log-transformed). There was also variation in the number of species of ECM fungi which were apparently specific to particular host genera, values ranging from zero (in 15 genera) to >40 in the case of Betula and Fagus. In total, 233 fungal species appeared to be specific to a single host genus (i.e. 40% of those surveyed). Comparison of the ECM mycota associated with different host genera by PCA accounted for 17% of the total variation, with genera belonging to the Fagaceae (Quercus, Fagus and Castanea) tending to cluster together, indicating a degree of overlap in their ECM associates. Exotic conifer species, which displayed a lower ECM diversity than would be expected from their distributional areas, were characterized by a high degree of overlap with the ECM associates of Pinus and Betula. These results indicate that the abundance of different genera of host trees and variation in host specificity could provide a basis for understanding patterns of diversity in ECM fungi within Britain.

Variation in attack by the mahogany shoot borer, Hypsipyla grandella (Lepidoptera: Pyralidae), in relation to host growth and phenology

Abstract: In order to evaluate the relationships between attacks by the mahogany shoot borer Hypsipyla grandella (Zeller) and host growth and phenology, field trials of Spanish cedar Cedrela odorata and American mahogany Swietenia macrophylla established in Costa Rica were assessed intensively over an 84 week period. Height growth of C. odorata was approximately twice that of S. macrophylla , with mean growth rates of 2.0 and 1.3 cm week −1 respectively. Cedrela odorata displayed pronounced temporal variation in leaf phenology, with a minimum of 51% of trees in leaf during a relatively dry period. In contrast, the minimum proportion of foliated S. macrophylla trees was 87%. No shoot borer attacks were recorded on S. macrophylla until week 50 after the onset of assessments, whereas initial attacks of C. odorata were recorded during week 6. By week 84, the proportion of trees attacked was 74% and 77%, respectively. In both species, attacks were concentrated in seasonal peaks, coinciding with the production of new shoots. Pronounced spatial variation in attack was observed in both species. At week 12, the number of attacks per block in C. odorata was negatively correlated with available calcium concentration (r=0.85, P C. odorata was positively correlated with available phosphate concentration (r=0.84; P C. odorata and 0.4% S. macrophylla remained undamaged to a height of 3 m. It is suggested that control methods for the mahogany shoot borer should take account of temporal dynamics in attack, and relationship to host phenology. Manipulation of the soil nutrient status may also form part of an integrated approach to pest management.

The effect of cultivar mixtures on malting quality in winter barley

Abstract: A range of winter barley cultivars was grown, either as pure stands or as components of mixtures, in a trial in 1995-96. For malting quality characters, mean values of mixtures did not differ from mean values of the appropriate monocultures, except for decreases in homogeneity, as determined by a fluorescence test of cell wall modification. When disease pressure was modified by fungicide, hot water extract was not significantly altered, although this may have been due to the restriction of malting to grain retained by a 2.5 mm sieve. One mixture, comprised of three related winter malting cultivars, gave higher hot water extracts than its components, as pure stands, with no adverse effects on homogeneity. This was not simply attributable to lower grain nitrogen content.

Ectomycorrhizal colonisation of Sitka spruce [Picea sitchensis (Bong.) Carr] seedlings in a Scottish plantation forest

Abstract: The ectomycorrhizal (ECM) colonisation of seedling Sitka spruce (Picea sitchensis) was examined in an uneven-aged plantation forest in southern Scotland. The extent of ECM colonisation of individual seedlings was 43.8–97.2%, with an overall mean of 80.3 ± 1.1%. A total of 13 ECM morphotypes were differentiated, with 1–4 ECM types colonising an individual seedling. ECM colonisation was dominated by a single species, Tylosporafibrillosa, which accounted for 72.4–97.7% of the ECM colonisation recorded, on a plot mean basis. Other ECM types appeared to be distributed very patchily, only two types (Lactarius sp. and Mycelium radicis atrovirens Melin) exceeding a mean of 10% colonisation in any one plot. No significant correlations were recorded between ECM colonisation and seedling growth, or between ECM colonisation and soil pH, loss-on-ignition, or water content.

Temporary partial breakdown of mlo-resistance in spring barley by sudden relief of soil water-stress under field conditions: the effects of genetic background and mlo allele

Abstract: This study, carried out under field conditions, assessed the extent to which temporary breakdown of mlo-resistance, following relief of water-stress, was determined by genetic background and mlo allele. Commercial barley cultivars expressing the mlo gene for resistance to powdery mildew (Erysiphe graminis (Blumeria graminis) f.sp. hordei) were tested as well as doubled haploid progeny from spring barley genotypes, a proportion of which were sown in the field in two successive years. Plants were protected from natural rain by a mobile rain shelter and either watered by trickle-irrigation or allowed to dry. Percentage mildew infection resulting from natural inoculum was recorded and the doubled haploid genotypes were classified as resistant, intermediate or susceptible on the basis of their control (watered) treatment scores. In each of the three designated classes, particular genotypes developed infection levels, following relief of water-stress, that were higher than those observed on the well-watered controls. This was found not to be related to the mlo allele as there was no significant difference between the increases observed on resistant plants carrying mlo9 and resistant plants carrying mlo11. Differences in the degree of breakdown of resistance were attributed to genetic background rather than to the specific mlo allele.

Diversity and Complexity of Erysiphe graminis f.sp. hordei Collected from Barley Cultivar Mixtures or Barley Plots Treated with a Resistance Elicitor

Abstract: Powdery mildew populations were analysed to determine the effects of a resistance elicitor and cultivar mixtures on genetic complexity and diversity. Isolations were made from a range of spring barley monocultures and mixtures in a field trial, and characterised for virulence and RAPD profile. In a second trial, isolates were taken from a single mixture from untreated and resistance elicitor-treated areas and from the components of the mixture in monoculture. The mildew population was not only highly heterogeneous for virulence characteristics, but also proved heterogeneous within pathotypes for molecular markers, indicating the major impact of sexual recombination on population structure and the lack of clonal dominance. Various diversity measurements were compared and the value of dissimilarity measurement for revealing genetic distance within a population was highlighted. There was a trend towards increasing complexity as the season progressed, but there was no consistent relationship between cultivar or mixture, disease control treatment, fertiliser treatment, replicate or position in trial, and pathogen genotype. Whilst the resistance elicitor did reduce mildew by 78% in the first trial, and there was no interaction with fertiliser level in its expression, control was substantially less in the second trial. There were no differences between mildew isolates from elicitor and control treatments. It was felt that more effective and consistent resistance elicitors need to be developed before it can be stated that they are unlikely to be eroded by selecting resistant or adapted mildew genotypes.

Exploration and exploitation strategies of powdery mildew on barley cultivars with different levels of nutrients

Abstract: The mass fractal dimension (MFD) of colonies of mildew (Erysiphe graminis f.sp. hordei) growing on barley was calculated as a measure of their spatial structure. Despite the elongated shape of the colonies imposed by the leaf cellular structure, the MFD remained constant with scale. The mildew MFD differed on different cultivars of barley, and was greater on leaves produced under higher nutrient level indicating a physiological component. Lower MFD values correspond with the thin spreading growth associated with exploration strategies and higher values correspond to the denser, more branched structure associated with exploitation of the substrate. Cultivars showing exploration strategies induced by resistance expression responded to increased nutrient levels more than those expressing little resistance such as Golden Promise.

Genetic variation in Fitzroya cupressoides cultivated in the British Isles, assessed using RAPDs

Abstract: Fitzroya cupressoides (Molina) Johnston (Cupressaceae), a threatened conifer native to southern South America, has been cultivated in a number of gardens and arboreta in the British Isles since its introduction in 1849. In order to assess the importance of these cultivated trees for ex situ conservation, foliar samples were collected from 48 trees from throughout the British Isles, including five of known wild origin (Chile). DNA was extracted from these samples and assessed using the RAPD technique, in order to examine the extent of genetic variation. All samples from the cultivated trees of unknown origin, with one exception, were found to be genetically identical. In contrast, the five samples of known wild origin revealed pronounced polymorphism, varying from 5.3% to 49.1% between individuals. These results suggest that virtually all of the F. cupressoides trees currently cultivated in the British Isles have been derived from a single individual by vegetative propagation. Their value for ex situ conservation is therefore likely to be extremely limited. The implications of these results for the genetic conservation of other taxa in gardens and arboreta is discussed.

The interaction of humidity and resistance elicitors on expression of polygenic resistance of barley to mildew

Abstract: Elicitor-active glucan was applied to leaves of genotypes of barley expressing different levels of resistance to powdery mildew (Erysiphe graminis f. sp. hordei)which was assessed by measuring mildew colonies per leaf or speed of papilla induction response to mildew challenge. The influence of humidity was also assessed by treating leaves with glucan, inoculating with mildew and immediately sealing the leaves in Perspex containers in an apparatus which enabled temperature, air speed and humidity to be controlled accurately. In water-treated controls low humidity alone reduced colonies per leaf, and at 60% r.h. genotype 7204 showed significantly less effect of humidity compared with other genotypes, although at 40% it responded as other genotypes. At low humidity glucan stimulated resistance for genotypes Proctor and 7204 but not for Golden Promise or 9855; the effect of humidity or elicitor alone was only significant on genotype 7204, Chitin also proved an effective elicitor, but at high and not at low humidity. Time of pre-treatment before mildew challenge, leaf stage, type of elicitor, concentration of elicitor, post-inoculation light regime, mildew isolate and barley genotype all had major influences on papilla response. Other factors were less important. Based on papilla formation, the barley cultivar Proctor was most and Golden Promise the least responsive to glucan as an elicitor. The potential for exploiting the genetic basis of inducible resistance is discussed. Zusammenfassung Blatter von Gersten-Genotypen, die tmterschiedlich re-sistent gegen Echten Mehltau (Erysiphe graminis f. sp. hordei)waren, wurden mit elicitor-aktivem Glukan behandelt. Das AusmaB der Resistenz wurde anhand der Zahl der Mehltaukolonien auf den Blattern oder der Geschwindigkeit der Induktion einer Papillenbildung nach voratisgegangener Mehltauinokulation gemessen. Der Einflus der Luftfetjchtigkeit wurde bestimmt, indem die Blatter mit Glukan behandelt, mit Mehltau inokuliert und unmittelbar danach in Acrylglasbehalter in einem Gerat eingeschlossen wurden, in dem Temperatur, Luft-geschwindigkeit und Feuchtigkeit genau kontroUiert wer-den konnten, Bei den mit Wasser behandelten Kontrollen reduzierte bereits eine niedrige Luftfeuchtigkeit die Zahl der Kolonien pro Blatt, Bei 60% relativer Luftfeuchtigkeit war der Einflus der Luftfeuchtigkeit bei Genotyp 7204 signifikant niedriger als bei den anderen Genotypen, bei 40% war jedoch kein Unterschied zu den anderen Genotypen festzustellen. Die Glukanbehandlung for-derte bei niedriger Luftfeuchtigkeit die Resistenz bei den Genotypen Proctor und 7204, nicht aber bei Golden Promise und 9855, Luftfeuchtigkeit oder Elicitor allein wirk-ten sich nur bei Genotyp 7204 signifikant aus, Auch Chitin war ein wirksamer Elicitor, jedoch nur bei hoher und nicht bei niedriger Ltiftfeuchtigkeit, Der Zeitpunkt der Behandlung vor der Mehltauinokulation, das Ent-wicklungsstadium, die Art und die Konzentration des Elicitors, die Lichtverhaltnisse nach der Inoktilation, das Mehltauisolat und der Genotyp der Gerste wirkten sich stark auf die Papillenbildung aus, wahrend andere Eakto-ren weniger bedeutend waren, Gemessen an der Papillenbildung reagierte die Gerstensorte Proctor am starksten und Golden Promise am wenigsten auf den Elicitor Glukan, Das Potential fur die Nutzung der genetischen Basis der induzierbaren Resistenz wird diskutiert.

Heterokaryosis and vegetative incompatibility in Stagonospora nodorum

Abstract: Heterokaryotic colonies of Stagonospora nodorum consist of a fine mosaic of individual cells of the two component genotypes that are linked by frequent hyphal anastomosis. The intimate mixing does not extend to the colony edge where 1 mm3 blocks of hyphae all of the same genotype occur. Col- onies developed from single pycnidiospores from heterokaryons were homokaryotic and segregated into the two component genotypes, demonstrating that all the nuclei in a spore are of the same geno- type. Spore progenies from single pycnidia produced by heterokaryons, however, were frequently geneti- cally heterogeneous, indicating that these asexual fruiting structures are not uninucleate in origin. The nuclear ratio in heterokaryons was characteristic of the component genotypes and could deviate mark- edly from 1: 1 with no reduction in growth. Only 1.6% of pairs of physiologically-different nitrate non- utilizing mutants from different strains showed com- plementation, indicating that vegetative incompati- bility is widespread in S. nodorum. The few compati- ble strains had common origins and may be clonally related. Tests on a limited number of combinations suggested that vegetative incompatibility could not be overcome by protoplast fusion. Attempts to isolate so- matic heterozygous diploids and parasexual recom- binants were largely unsuccessful. Heterokaryosis and parasexuality do not appear to be significant sources of natural variation in this fungus.

Information technology in epidemiology

Abstract: Information technology (IT) has been available for many years but recent developments have provided new opportunities. All areas of science can and will benefit greatly from the further development of information technology over the next few years. As with other new technologies, or accelerated developments of existing technologies, IT will provide most benefit when adapted appropriately to the existing tools available for the conduct of science investigations. Time will provide the answer to whether the recent IT developments described here will revolutionalize plant pathology on the same scale as previous developments such as those in microscopy and molecular biology.

Analysis of spatial trends in field trials using semiparametric additive models

Abstract: We extend semiparametric models to models which combine parameterised treatment effects with any number of smooth terms. We derive explicit expressions for the estimates of the parametric part of the model and the standard errors; in addition, several methods of model selection are presented. We examine data from a barley trial to show that these models provide a flexible representation of environmental trends in field experiments.