Showing papers by "Adrian C. Newton published in 1997"

Genetic variation in Costa Rican populations of the tropical timber species Cedrela odorata L., assessed using RAPDs

Abstract: Cedrela odorata L. (Spanish cedar), an economically important timber species native to the American tropics, is the focus of increasing conservation concern due to high rates of deforestation within its native range. To assess the extent of the genetic diversity within and between populations of this species, samples were obtained from 10 widely dispersed populations within Costa Rica and analysed for random amplified polymorphic DNA (RAPD) variation. Fourteen 10-mer primers were used to generate 97 polymorphic RAPD bands. Presence/absence data for all bands were subjected to a pairwise genetic distance analysis, according to Jaccard's coefficient, then neighbour-joining cluster analysis was performed on these distances, as was an analysis of molecular variance (AMOVA), to assess levels of differentiation between populations and regions, and Shannon's Diversity Index was used to quantify levels of diversity within and between populations. Results indicated highly significant genetic differentiation (P < 0.004, AMOVA) between populations originating from the North Pacific and Atlantic/South Pacific regions of Costa Rica, with 35.3% of the total variation attributable to a difference between these areas. Little differentiation was recorded between populations from within the same region (P= 0.757, AMOVA), and 65.1% of the total variance was attributable to variation within populations. Estimated values for within-population diversity, calculated as Hpop/Hsp by means of Shannon's Diversity Index, were found to vary greatly between primers, but the overall within-population component of genetic diversity was 0.45. Possible reasons for the high degree of intraspecific genetic variation within this species are discussed and the implications of these results for the conservation and use of its genetic resources are described.

The effect of component number on Rhynchosporium secalis infection and yield in mixtures of winter barley cultivars

Abstract: Mixtures of winter barley cultivars containing up to six components were grown over three years with and without fungicide treatment. Yield increases were recorded for mixtures compared with the mean of their monoculture components and there was a significant trend towards greater benefit from increased number of components. These benefits were partially attributable to a corresponding increase in control of Rhynchosporium secalis as component number increased. The potential for exploitation of mixtures in cereals for control of splash-dispersed pathogens is discussed.

The effects of propagation environment and foliar area on the rooting physiology of Cordia alliodora (Ruiz & Pavon) Oken cuttings

Abstract: The effects of propagation microclimate and foliar area on the rooting of Cordiaalliodora (Ruiz & Pavon) Oken cuttings were investigated using non-mist propagators with and without shade. Photosynthetic rates (Pn), stomatal conductance (gs) and chlorophyll fluorescence ratio (Fv/Fm) of the cuttings were assessed during propagation. Pronounced differences in microclimate were recorded between treatments, with lower temperatures and vapour pressure deficit (VPD) under shade. During the first 8 days after insertion, Pn varied between 2.21 and 4.96 and 0.47 – 2.54 μmol CO2 m – 2s – 1 in the shaded and unshaded propagators, respectively. In the unshaded propagator, Fv/Fm decreased to a minimum of 0.72 2 days after insertion, recovering thereafter. In two separate rooting experiments, rooting percentage was reduced by high irradiance in the 20 and 30 cm2 leaf area treatments, but not in the 10 cm2 treatment. Pn decreased with an increase in leaf area in both shaded and unshaded propagators. Fv/Fm also declined with increasing leaf area in the high irradiance treatment. PAR and Pn were positively correlated under shade (r2 = 0.51) but negatively correlated in the unshaded treatment (r2 = 0.49); maximum Pn values were recorded at a PAR of 400 μmol m – 2 s – 1. No significant differences in gs were found between treatments, values ranging between 130 and 194 mmol H2O m – 2 s – 1. Positive correlations were found between rooting percentage and mean Fv/Fm. These results indicate that rooting of C. alliodora cuttings is related to photosynthetic activity during propagation, which is itself influenced both by propagator microclimate and cutting leaf area.

Detection of Polymorphism in Puccinia hordei using RFLP and RAPD Markers, Differential Cultivars, and Analysis of the Intergenic Spacer Region of rDNA

Abstract: A world-wide range of isolates of Puccinia hordei and P. striiformis f. sp. hordei and UK isolates of P. striiformis f. sp. tritici and P. recondita were characterized using DNA restriction fragment length polymorphisms (RFLPs), random amplified polymorphic DNAs (RAPDs), ribosomal DNA (rDNA) intergenic sequence (IGS) or virulence on differential cultivars. The different species were readily distinguished by both RFLPs and RAPDs. Within a species, variability was detected using differential cultivars, RAPDs, and RFLPs with probes from the rDNA region, indicating their potential for population analysis. However, RFLPs within a species were not detected using a wide range of random (anonymous) probes from a P. hordei genomic library. Previous assumptions about the general uniformity of rust genotypes were reassessed from these data.

Resistance elicitors as crop protectants

Abstract: crop protectants A C Newton, S K Miller1, G D Lyon, T Reglinski2 Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, Scotland, UK. Induction of plant resistance mechanisms by application of elicitors is becoming a realistic component of integrated crop ptotection strategies. Whilst resistance elicitors are active on a wide range of crops, optimum control may be achieved by targeting specific host-pathogen interactions with particular molecules. We are developing approaches for targeting broad protection and specific diseases to achieve optimum disease control and yield benefit. Mildew on elicitor treated (left) and untreated (right) barley cv. Golden Promise.