Showing papers by "Adrian C. Newton published in 1991"

Mineral nutrition and mycorrhizal infection of seedling oak and birch

Abstract: summary In order to assess the factors influencing the extent and composition of ectomycorrhizal infection, and the consequences for seedling growth, seedlings of oak (Quercus robur L.) and birch (Betula pendula Roth.) were established in both field plots and pots of soil from two forested sites (Thetford Chase and Leith Hill). Seedlings were harvested after one growing season, and analysed for ectomycorrhizal infection. When a single root system of pot-grown oak was analysed in detail seven mycorrhizal types were differentiated. The relative abundance of these types varied depending on whether infection was assessed by counting branched mycorrhizas, or individual mycorrhizal tips. This reflected variation in the pattern of branching of the different mycorrhizal types. Of the 41 mycorrhizal types differentiated in the entire survey of 1800 seedlings, five were consistently recorded as unbranched, and six were found to produce second-order branches. Different mycorrhizal types displayed contrasting patterns of abundance, both with respect to site and host species. For example, 21 types were recorded infecting oak, whereas only 15 were found on birch; only three types were found infecting both oak and birch on both sites. In this survey, seedlings tended to be dominated by between one and three mycorrhizal types. Two types were particularly dominant: those formed by Scleroderma citrinum (Pers.) and Paxillus involutus (Batsch) Fr., which accounted for up to 61 and 92 % of the mycorrhizas of oak and birch respectively. These fungi were exceptional amongst those encountered in the present analysis, in producing both highly branched mycorrhizas and mycelial strands. The relationship between ectomycorrhizal infection and seedling growth was assessed by correlation. Total seedling dry mass was in general found to be positively correlated with the total number of ectomycorrhizal tips, but poorly correlated with the extent of ectomycorrhizal infection, except where seedling growth had previously been shown to be limited by phosphate availability (i.e. in the case of pot-grown birch on soil from Leith Hill). Seedling dry mass was also in general poorly correlated with number of mycorrhizal types, with two exceptions (i.e. field-grown oak and pot-grown birch on soil from Thetford Chase). These results are discussed in the context of the role of ectomycorrhizal infection during seedling establishment, and implications for the methodologies utilized in assessing mycorrhizal infection are highlighted.

Mineral nutrition and mycorrhizal infection of seedling oak and birch II. The effect of fertilizers on growth, nutrient uptake and ectomycorrhizal infection

Abstract: SUMMARY In order to determine the effect of fertilizers on the growth, nutrient uptake and ectomycorrhizal infection of seedling oak (Quercus robur L.) and birch (Betula pendula Roth.), N, P and K fertilizers were applied in a factorial design to plots of seedlings artificially established on two woodland sites on nutrient-poor soils. A parallel series of pot experiments were undertaken using the same design, in order to eliminate the effects of neighbouring mature trees on growth and mineral uptake. Fertilizer addition increased the growth of birch in both pot and field experiments, and on both soil types, by up to 390%. In contrast, fertilizer addition had little effect on growth of oak, other than to increase dry mass by 11 % in one of the pot experiments. Application of N, P and K generally increased the foliar concentration of the respective nutrient, by up to 49 %. However, a number of negative effects of fertilizer application were recorded, particularly in the case of foliar P. For example, application of N, K and N x K reduced the foliar P of birch by up to 35 % in pots. Fertilizer application to both species tended to reduce ectomycorrhizal infection, both in pots and in the field. These effects were more pronounced for birch than oak, and a greater number of effects were recorded in pots than in the field. In general, N had the greatest effect. For example, the number of mycorrhizal tips of birch in pots was reduced to 38 % of the control value, following N application. Application of P and K also reduced mycorrhizal infection, although the results of the analyses differed depending on how mycorrhizal infection was assessed. The relative proportions of a number of the ectomycorrhizal types were also influenced by fertilizer addition. Although the proportion of most types was reduced, two types [formed by Paxillus involutus (Batsch) Fr. and Scleroderma citrinum Pers.] increased in some of the treatments where they were dominant. For example, application of N to birch in pots increased the proportion of P. involutus mycorrhizas to 172 % of the control. The interactions between the effect of fertilizers on growth, nutrient uptake and mycorrhizal infection are discussed, and some implications for forest management are highlighted.

Mineral nutrition and mycorrhizal infection of seedling oak and birch. I, Nutrient uptake and the develoment of mycorrhizal infection during seedling establishment

Abstract: In order to assess the importance of nutrient uptake and mycorrhizal infection for the establishment of seedlings of pedunculate oak (Quercus robur L.) and silver birch (Betula pendula Roth.), seedlings were grown on two nutrient-poor soils and sequential harvests taken throughout the first growing season. Seedlings were artificially established in two woodland sites and in pots of soil collected from each field site (...)

Recurrent Selection for Adaptation of Erysiphe graminis f. sp. hordei to Partial Resistance and the Effect of Environment on Expression of Partial Resistance of Barley

Abstract: Five isolates of powdery mildew were subjected to recurrent selection on partially resistant barley cultivars and tested at intervals for adaptation to overcome partial resistance. A trend towards adaptation to the recurrent host was observed in infection frequency data, but biomass per colony, measured using sterol cell-wall determinations and enzyme linked immunosorbent assay, was not greatly affected. The expression of partial resistance was examined after seedling growth under two different environmental regimes. Significant interactions with both overall resistance expression and latent period were detected using infection frequency data, and the effects were both cultivar and isolate dependent. Variability between single colony derivatives of an isolate, which had previously shown adaptation to a partially resistant cultivar, was detected in infection frequency data indicating instability and a non-nuclear component to adaptation.

The effect of specific and non-specific resistance in mixtures of barley or genotypes on infection by mildew ( Erysiphe graminis f. sp. hordei ) and on yield

Abstract: Preliminary field trials indicated that the yields of mixtures of barley cultivars partially resistant to mildew (Erysiphe graminis f. sp. hordei) were greater than those expected from the mean of their components. Subsequent trials in 1988, 1989 and 1990 demonstrated that such mixtures gave enhanced yield. However, fungicide treatment of mixtures gave significant positive and negative effects on yield. In mixtures with cultivars containing partial resistance there was evidence of a positive relationship between high yield loss due to mildew (low disease tolerance) in cultivars grown in monoculture and their yield advantage in mixtures. The converse resulted in yield disadvantage.

Characteristics of strains of Septoria nodorum adapted to wheat or to barley

Abstract: Sixty-four strains of Septoria which had been isolated from a range of hosts at different locations and in different years were characterized for their adaptation to wheat or barley, growth at near-maximum temperature, fluorescence, colony morphology, conidial (pycnidiospore) length and hexokinase and alkaline phosphatase isozymes. For each character except conidial length, the strains could be divided into two or three discrete groups. The variation in these six characters was strongly associated, such that 60 strains could be classified into two groups, designated W-type and B-type. W-type strains are adapted to wheat, produce large colonies at 31 C, fluoresce, produce brown-pigmented colonies, and have fast isozymes. B-type strains are adapted to barley, produce small colonies at 31 C, do not fluoresce, produce pink-pigmented colonies, and have slow isozymes. A few strains differed from these norms in one of the six characters, but only one showed an atypical host adaptation. The four unclassified strains differed from W- or B-type in two or more characters. The many differences between the W- and B-types suggest they are genetically distinct populations within Septoria nodorum.

Isozyme Variability in Isolates of Some Facultative Phytopathogenic Fungi

Abstract: Gel electrophoresis was used to examine the variation in isozymes within and between the facultative pathogen species Septoria nodorum, Ustilago maydis and Rhynchosporium secalis. Variation was found in all three species, U. maydis being the most variable. The variation between isolates of R. secalis was sometimes unstable, reflecting variability in other characters. The determinants of isozyme variability, particularly in relationship to the general biology of different fungi, are discussed.