Showing papers by "Adrian C. Newton published in 1992"

Towards a functional classification of ectomycorrhizal fungi

Abstract: Ectomycorrhizal (ECM) fungi have previously been divided into two groups (‘early-stage’ and ‘latestage’) based on their position in ‘ectomycorrhizal succession’. This classification has a number of limitations, particularly in the lack of precision in the terminology adopted and its general applicability. Many species cannot be easily assigned to either stage, and the behaviour of some species is modified by environmental conditions. In addition, a number of different mechanisms of ECM succession have been proposed, including the influence of organic matter and root exudates. In this paper, it is suggested that the phenomenon of ECM succession can be explained simply by the relative ability of different fungi to colonize and spread from different sources of inoculum. Epidemiological characteristics, such as the ability to produce mycelial strands or to spread on root systems by secondary infection, may therefore provide a more appropriate basis for a functional classification of ECM fungi. The functionally important characteristics of ECM fungi are discussed.

Mahogany conservation: status and policy initiatives.

Abstract: Genuine or American mahogany is obtained from trees of the genus Swietenia (S. mahagoni, S. macrophylla, and S. humilis), and is one of the premier timbers of international commerce. The trade in mahogany commenced almost five centuries ago with S. mahagoni from the Caribbean; but following ‘commercial’ extinction of this resource, trade became centred on mahogany populations in South and Central America (S. macrophylla). The trade in mahogany is predominantly from primary forests, and has led to population and genetic resource declines — particularly in the Caribbean and Central America. More recently, there have been an increasing number of ‘commercial’ extinctions in South America. As the resource declines, pressures mount to accelerate the illegal extraction of mahogany from National Parks and lands reserved for indigenous (‘Indian’) peoples. Inability to control this trade threatens mahogany populations and genetic resources throughout its range, at the same time adversely affecting the livelihoods of indigenous peoples in the process.Mahogany often regenerates poorly following logging operations that are conducted using current management practices, and further research is required to determine the optimum biological and economic conditions for in situ silviculture. Attempts to cultivate mahogany in plantations have met with little success in the Americas, due mainly to effects of the shoot-borer (Hypsipyla grandella), a moth larva that damages terminal shoots, so leading to excessive branching and reduced timber value (Figs 3 and 4). The success of mahogany plantations in the neotropics will require the development of an integrated pest-management system, perhaps involving the incorporation of pestresistant genotypes within agro-forestry or mixed plantation systems.It is vital that appropriate silvicultural and trade practices are adopted to ensure sustainable mahogany extraction, while at the same time conserving an adequate population and genetic resource-base. To this end, effective trade monitoring and resource-regulation measures must be introduced to assist in controlling illegal trade and to encourage a scientifically managed, sustainable, utilization of mahogany. Two of the three mahogany species, S. humilis and S. mahagoni, have been listed in Appendix II of the Convention on International Trade in Endangered Species (CITES). The third and only other recognized species of Swietenia, S. macrophylla, should also be considered for listing in CITES Appendix II, thereby benefiting from the international trade-monitoring and resource regulation requirements consequent upon such listing.

The influence of leaf area on the rooting physiology of leafy stem cuttings of Terminalia spinosa Engl.

Abstract: The effect of different leaf areas on the rooting of Terminalia spinosa Engl. cuttings in an non-mist propagation system in glasshouses at Edinburgh was investigated by trimming the leaves to 0, 7.5, 15 and 30 cm2 before cuttings were severed from stockplants. Cuttings were taken to a standard length of 5 cm from the lateral shoots of previously pruned stockplants grown in a tropicalised glasshouse. During the rooting period, photosynthetic rate, stomatal conductance, water potential and relative water content of the cuttings were assessed at regular intervals. It was found that (i) removal of the entire leaf area prevented rooting; (ii) cuttings with a 7.5 cm2, 15 cm2 and 30 cm2 leaf all achieved 80% rooting after 3 weeks; (iii) an increase in leaf area from 7.5 cm2 to 30 cm2 increased the rate of rooting and the length of the longest root after 2 weeks, but also increased the number of original leaves abscised after 6 weeks; and (iv) the greatest number of new leaves were produced by cuttings with 7.5 cm2 and 15 cm2 leaf area per cutting. All leafy cuttings actively photosynthesized during the propagation period, with a mean rate of 2 μmol CO2 m-2 s-1 with an irradiance of 100 μmol m-2 s-1. Cuttings with 30 cm2 leaf area had lower relative water contents, lower stomatal conductances and lower photosynthetic rates per unit leaf area than those with a 7.5 cm2 and 15 cm2 leaf. It was concluded that T. spinosa cuttings are easy to root, provided the cuttings have leaves to produce current assimilates.

Evaluation of sources of partial resistance to mildew in barley using enzyme-linked immunosorbent assay and other assessment methods

Abstract: Twenty-nine spring barley genotypes ranging from primitive landraces to modern cultivars were characterised for partial resistance to powdery mildew on detached leaves and in the field Detached seedling and adult plant leaves were produced under spore-free glasshouse conditions and were assessed for infection frequency (IF) and then total mildew biomass using enzyme-linked immunosorbent assay (ELISA), and thereby biomass per colony (BMC), following controlled infection Field plants were assessed visually for infection and for total mildew biomass using ELISA Several genotypes were identified as having below average IF and BMC on both seedling and adult detached leaves and field scores of leaf area infected with mildew IF at the seedling stage was highly correlated with IF at adult plant stage and with mildew biomass in the field Adult plant IF was highly correlated with visual field scores BMC data were often negatively correlated with other assessments

Selection for Aggressiveness in Erysiphe graminis f. sp. hordei Towards Partial Resistance in Barley

Abstract: Isolates of powdery mildew were subjected to recurrent selection on partially resistant barley cultivars for 76 inoculation cycles over three years. Previous intermediate tests on up to 32 cycles for adaptation to overcome the host resistance revealed a trend towards adaptation to the cv. 7204 recurrent host in infection frequency data but not towards cv. Golden Promise or 9319. Subsequent cycles demonstrated adaptation to these latter hosts also. . , . .