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Showing papers by "Adrian C. Newton published in 1994"



01 Jan 1994
TL;DR: Suggestions are made for experimental approaches to improve the understanding of the mechanisms of rooting of leafy stem cuttings, including the development of a mechanistic model of adventitious root development and the practical implications arising from a process-based approach to propagation.
Abstract: Vegetative propagation offers the opportunity to rapidly overcome the limitations to domestication imposed by long generation times, irregular fruiting/flowering and outbreeding. Vegetative propagation techniques are increasingly being applied to a wide range of tree species, of both moist and dry tropics. Identification of the critical factors determining adventitious root development is crucial to sustained, cost-effective propagation, even in 'species in which these factors are not currently limiting. Over the past ten years, research at ITE has identified a wide range of factors which influence rooting, including the stockplant growth environment, cutting origin, post-severance treatments applied to cuttings, and the propagation environment. In order to understand the influence of these different factors and their interactions, an appreciation of the physiological, biochemical and cytological processes involved in rooting is required. The primary processes occurring in the leaf are net photosynthesis and transpiration, while those in the stem are starch hydrolysis, translocation of sugars, water and nutrients, respiration, mitosis and cell differentiation. Each of these processes is influenced by a number of environmental, morphological and physiological variables, such as leaf area and thickness, internode length, chlorophyll content, stomatal density stem Uglification, etc. Suggestions are made for experimental approaches to improve further the understanding of the mechanisms of rooting of leafy stem cuttings. These approaches include the development of a mechanistic model of adventitious root development. The practical implications arising from a process-based approach to propagation are also discussed.

67 citations


Journal ArticleDOI
TL;DR: A computer-based training programme was evaluated for standardising assessments, and was found to improve assessors' accuracy, and some modifications to the barley field scoring system are suggested to improve comparability between assessors.
Abstract: The severity of mildew on barley is usually assessed visually and this leads to variation between different scorers. Field assessments by four assessors were analysed to determine the nature and degree of subjective discrepancies between assessors. Two inexperienced assessors failed to detect a major effect of nitrogen due to differences in the interpretation of a scoring system. A computer-based training programme was evaluated for standardising assessments, and was found to improve assessors' accuracy. Linear regression analysis was used here to resolve the error variance into components representing the accuracy and precision of the assessors. Plots of the cumulative differences between the estimate of disease severity by each assessor and the best estimate were used to display how the discrepancies varied with the level of disease. Some modifications to the barley field scoring system are suggested to improve comparability between assessors.

61 citations



Journal ArticleDOI
TL;DR: A number of markers were found to be diagnostic for particular species, which could be of value in determining the status of putative hybrids and the application of RAPDs to the study of genetic variation in mahoganies is discussed.
Abstract: Despite the economic importance of mahoganies (Meliaceae) little is known of the pattern of genetic variation within this family of tropical trees. We describe the application of a polymerase chain reaction (PCR)-based polymorphic DNA assay procedure random amplified polymorphic DNAs (RAPDs) to assess the extent of genetic variation between eight mahogany species from four genera. Pronounced genetic differentiation was found between the species and genera. There was a clear separation of Cedrela odorata from the other species, with 95% of the variable amplification products differing, whereas Lovoa trichilioides, Khaya spp. and Swietenia spp. were more closely grouped. These results are consistent with the current taxonomic viewpoint. A number of markers were found to be diagnostic for particular species, which could be of value in determining the status of putative hybrids. The application of RAPDs to the study of genetic variation in mahoganies is discussed in the context of developing genetic conservation and improvement strategies for these species.

49 citations


Journal ArticleDOI
TL;DR: Yeast cell-wall extracts (YE) had high phytoalexin elicitor activity on soybeans and induced resistance against barley powdery mildew in the normally highly susceptible cv.
Abstract: Summary Yeast cell-wall extracts (YE) had high phytoalexin elicitor activity on soybeans and induced resistance against barley powdery mildew in the normally highly susceptible cv. Golden Promise. Following treatment with YE there was rapid stimulation of phenylalanine ammonia-lyase (PAL) activity and faster formation of papillae in response to attempted fungal penetration. The spray adjuvants Agral and LI-700 each had poor phytoalexin elicitor activity and caused a slight enhancement of papilla formation and a low level of mildew control. The addition of the adjuvant to YE did not affect phytoalexin elicitation on soybeans but significantly enhanced the speed and the extent of PAL activity, papilla formation and mildew control. It is proposed that this is due to greater coverage and improved persistence enabling increased uptake of YE into the barley leaves.

38 citations



Journal ArticleDOI
TL;DR: A discrete model of the nearest neighbour type is used to model the growth and spread of fungal disease in a two-cultivar mixture assuming an unspecialized pathogen and geometrical patterns can eventually be interpreted once initial oscillations have subsided.
Abstract: A discrete model of the nearest neighbour type is used to model the growth and spread of fungal disease in a two-cultivar mixture assuming an unspecialized pathogen. Disease dynamics and dispersal are represented by a spatial, single pathotype version of Gumpert's (1992) model that simulated the temporal evolution of a number of pathotypes on a cultivar mixture. Spore dispersal occurs by discrete rules between a cell and its four orthogonal neighbours in a rectangular grid. Parameters termed transmission efficiency rates control the extent of successful inoculum exchange between two neighbouring cells depending on the cultivars present. Spatially averaged disease progress curves are computed for regular block and strip patterns in addition to the mean curve for twenty 1:1 random mixture patterns. These sets of curves are exhibited relative to the appropriate pure stand comparison for a range of auto- and cross-deposition parameters. We conducted simulations for uniform initial infection and also averaged over 20 random initial infection patterns at a comparable mean level. In the former case, provided the ratio of cross-deposition to auto-deposition is high enough and the disease progress curves take sufficiently long to reach their saturation value, the ranking of the geometrical patterns can eventually be interpreted once initial oscillations have subsided. The geometry with the largest proportion of links between neighbouring cells of different cultivar type generally corresponds to the lowest average disease level, but not for averaged simulations based on random initial infection patterns.

25 citations


01 Jan 1994
TL;DR: It is suggested that the development and implementation of a domestication strategy for mahoganies should be given high priority if a sustainable resource of mahogany is to be guaranteed in the 'future'.
Abstract: Despite the economic importance of mahoganies, few attempts have been made at genetic improvement, partly because of the high incidence of pest attack when mahoganies are grown in areas where they are native. A suggested domestication strategy for mahoganies is outlined, centred on the selection for pest resistance as part of a genetic improvement programme, the capture of selected genotypes using vegetative propagation techniques, and the deployment of selected material in appropriate silvicultural systems which optimise pest control. Current progress in developing such a strategy is described, including the assessment of genetic variation using field tests and molecular methods, and the development of vegetative propagation techniques with in vitro approaches. The importance of conserving genetic resources of mahogany species is highlighted, and the prospects for the future development of a domestication strategy are discussed. It is suggested that the development and implementation of such a strategy should be given high priority if a sustainable resource of mahogany is to be guaranteed in the 'future.

16 citations



Journal ArticleDOI
TL;DR: Barley genotypes representing a wide range of resistance expressions and origins, from major resistance genes in modern cultivars to field resistances in landraces, were assessed for tolerance to disease under glasshouse and field conditions to discuss the potential use of tolerance as a breeding character.
Abstract: Barley genotypes representing a wide range of resistance expressions and origins, from major resistance genes in modern cultivars to field resistances in landraces, were assessed for tolerance to disease under glasshouse and field conditions. A few genotypes were picked out as showing less yield loss than would be expected from the level of mildew infection. Genotypes showing more than the expected yield loss were also found. The potential use of tolerance as a breeding character is discussed.