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Leaf Position (leaf + position)
Selected AbstractsInfection of Blackcurrant Leaves by Drepanopeziza ribis in Relation to Weather Conditions and Leaf PositionJOURNAL OF PHYTOPATHOLOGY, Issue 5 2009Xiang Ming Xu Abstract Drepanopeziza ribis causes the leaf spot disease of blackcurrant (Ribes nigrum) and may lead to severe premature leaf-fall. Artificial inoculation studies were carried out to investigate infection of leaves by D. ribis conidia in relation to environmental conditions and leaf position (age) on cvs. Baldwin and Ben Hope in April and July 2007. All leaves on a number of selected extension shoots on potted three-year old plants were inoculated with conidia and then incubated under different conditions: 10, 17.5 and 25°C each with five wet periods (4, 8, 12, 24 and 30 h). Number of infected leaves was determined. The two cultivars differed significantly in their susceptibility to conidial infection: cv. Baldwin was much more susceptible than cv. Ben Hope. Older leaves on extension shoots were more susceptible to conidial infection than younger leaves. Increasing length of wetness duration led to increasing incidence of leaves infected, particularly when inoculated in July. However, the effects of temperature were inconclusive and generally very small in comparison with other factors. Field epidemics were monitored over three years (2005,07). Field data confirmed the main findings from controlled inoculation studies: severe disease was associated with very wet conditions and older leaves. Furthermore, they also suggested that significant disease increase only occurred from late July onwards. [source] A dynamic simulation model for powdery mildew epidemics on winter wheat,EPPO BULLETIN, Issue 3 2003V. Rossi A system dynamic model for epidemics of Blumeria graminis (powdery mildew) on wheat was elaborated, based on the interaction between stages of the disease cycle, weather conditions and host characteristics. The model simulates the progress of disease severity, expressed as a percentage of powdered leaf area, on individual leaves, with a time step of one day, as a result of two processes: the growth of fungal colonies already present on the leaves and the appearance of new colonies. By means of mathematical equations, air temperature, vapour pressure deficit, rainfall and wind are used to calculate incubation, latency and sporulation periods, the growth of pathogen colonies, infection and spore survival. Effects of host susceptibility to infection, and of leaf position within the plant canopy, are also included. Model validation was carried out by comparing model outputs with the dynamics of epidemics observed on winter wheat grown at several locations in northern Italy (1991,98). Simulations were performed using meteorological data measured in standard meteorological stations. As there was good agreement between model outputs and actual disease severity, the model can be considered a satisfactory simulator of the effect of environmental conditions on the progress of powdery mildew epidemics. [source] Infection of Blackcurrant Leaves by Drepanopeziza ribis in Relation to Weather Conditions and Leaf PositionJOURNAL OF PHYTOPATHOLOGY, Issue 5 2009Xiang Ming Xu Abstract Drepanopeziza ribis causes the leaf spot disease of blackcurrant (Ribes nigrum) and may lead to severe premature leaf-fall. Artificial inoculation studies were carried out to investigate infection of leaves by D. ribis conidia in relation to environmental conditions and leaf position (age) on cvs. Baldwin and Ben Hope in April and July 2007. All leaves on a number of selected extension shoots on potted three-year old plants were inoculated with conidia and then incubated under different conditions: 10, 17.5 and 25°C each with five wet periods (4, 8, 12, 24 and 30 h). Number of infected leaves was determined. The two cultivars differed significantly in their susceptibility to conidial infection: cv. Baldwin was much more susceptible than cv. Ben Hope. Older leaves on extension shoots were more susceptible to conidial infection than younger leaves. Increasing length of wetness duration led to increasing incidence of leaves infected, particularly when inoculated in July. However, the effects of temperature were inconclusive and generally very small in comparison with other factors. Field epidemics were monitored over three years (2005,07). Field data confirmed the main findings from controlled inoculation studies: severe disease was associated with very wet conditions and older leaves. Furthermore, they also suggested that significant disease increase only occurred from late July onwards. [source] Changes in leaf photosynthetic parameters with leaf position and nitrogen content within a rose plant canopy (Rosa hybrida)PLANT CELL & ENVIRONMENT, Issue 4 2000M. M. Gonzalez-Real ABSTRACT This paper deals with changes in leaf photosynthetic capacity with depth in a rose (Rosa hybrida cv. Sonia) plant canopy. Measurements of leaf net CO2 assimilation (Al) and total nitrogen content (Nl) were performed in autumn under greenhouse conditions on mature leaves located at different layers within the plant canopy, including the flower stems and the main shoots. These leaves were subjected (i) to contrasting levels of CO2 partial pressure (pa) at saturating photosynthetic photon flux density (I about 1000 ,mol m,2 s,1) and (ii) to saturating CO2 partial pressure (pa about 100 Pa) and varying I, while conditions of temperature were those prevailing in the greenhouse (20,38 °C). A biochemical model of leaf photosynthesis relating Al to intercellular CO2 partial pressure (pi) was parameterized for each layer of leaves, supplying corresponding values of the photosynthetic Rubisco capacity (Vlm) and the maximum rate of electron transport (Jm). The results indicated that rose leaves growing at the top of the canopy had higher values of Jm and Vlm, which resulted from a higher allocation of nitrogen to the uppermost leaves. Mean values of total leaf nitrogen, Nl, decreased about 35% from the uppermost leaves of flower stem to leaves growing at the bottom of the plant. The derived values of non-photosynthetic nitrogen, Nb, varied from 76 mmolN m,2leaf (layer 1) to 60 mmolN m,2leaf (layer 4), representing a large fraction of Nl (50 and 60% in layer 1 and 4, respectively). Comparison of leaf photosynthetic nitrogen (Np=Nl,Nb) and I profiles supports the hypothesis that rose leaves acclimate to the time-integrated absorbed I. The relationships between I and Np, obtained during autumn, spring and summer, indicate that rose leaves seem also to acclimate their photosynthetic capacity seasonally, by allocating more photosynthetic nitrogen to leaves in autumn and spring than in summer. [source] The microclimate under coloured hailnets affects leaf and fruit temperature, leaf anatomy, vegetative and reproductive growth as well as fruit colouration in appleANNALS OF APPLIED BIOLOGY, Issue 1 2010A. Solomakhin The purpose of this study was to investigate supposedly positive biological effects of coloured hailnets on microclimate, including photosynthetically active radiation (PAR), UV-B, air, soil, fruit and leaf temperature as well as humidity, which in turn may affect leaf anatomy, tree growth and fruit quality; apple was chosen as a model crop at Klein-Altendorf near Bonn, Germany; adjacent uncovered trees served as control. Red and green hailnets transmitted 3,6% more red or green light, without alteration of the red:far red (R,666 nm:FR,730 nm) ratio (0.99,1.01:1) and hence without affecting the phytochrome system. The microclimate was changed with a reduction by 12,23% in PAR and, to a larger extent, by 20,28% in UV, viz. shading. Light measurements at a 45° angle, to mimic the fruit or leaf position, showed that PAR was 90,210 µmol m,2 s,1 larger outside on a sunny summer day than under the white or red-white and 150,340 µmol m,2 s,1 larger than under red-black and green-black hailnets. Air temperature and relative humidity under coloured hailnets decreased by ca. 1.3°C and by ca 2% rh (cloudy) to 5% rh (sunny day), respectively, compared with outside; leaf temperature was decreased by up to 3°C and fruit temperature by up to 6°C. Soil temperatures at 5 cm depth were 0.5,1°C colder under red-black and green-black hailnets, but up to 0.9°C warmer under white and red-white hailnets compared with the uncovered control outside. Alternate bearing had a larger impact on vegetative growth in the affected year than the coloured hailnets; annual trunk diameter increments in cv. ,Fuji', i.e. the variety susceptible to alternate bearing, showed a larger variation than cv. ,Pinova' without alternate bearing. Reproductive growth, viz. return bloom and leaf anatomy were impaired by the coloured hailnets. Apple trees under dark hailnets developed thinner leaves with a thinner epidermis and fewer layers of palisade cells. These leaves were 3.5°C (dark hailnets) and 2.5°C (white hailnets) cooler than outside on a sunny day compared with ca. 1.5°C (dark hailnets) and 0.85°C (white hailnets) on a cloudy day. Transpirational cooling of cv. ,Fuji' leaves was 0.3,0.6°C outside and 1.4,1.6°C under the green-black hailnet on sunny days compared to <0.1°C on cloudy days. As a practical application, apple fruit colouration was dependent on light (PAR and UV-B) transmission of the respective hailnet colour. [source] Chemical composition and antimicrobial activity of the essential oil and CO2 extracts of the oriental tobacco, PrilepFLAVOUR AND FRAGRANCE JOURNAL, Issue 5 2002Radosav Palic Abstract A study of the chemical composition of essential oil and CO2 extracts of the middle and upper leaf positions of the oriental tobacco Prilep was performed using GC and GC,MS. The major constituents were: in the essential oil, neophytadiene and solanone; in CO2 extract I, neophytadiene; and in CO2 extract II, nicotine, nonacosane and solanesol. The antimicrobial activity of the essential oil and CO2 extracts were investigated against the microorganisms: Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The results showed that oil from the middle leaves showed greater activity than the oil of the upper leaves. Both leaf oils mainly showed greater activity than CO2 extracts. Copyright © 2002 John Wiley & Sons, Ltd. [source] Components of Partial Disease Resistance in Wheat Detected in a Detached Leaf Assay Inoculated with Microdochium majus using First, Second and Third Expanding Seedling LeavesJOURNAL OF PHYTOPATHOLOGY, Issue 4 2006R. A. Browne Abstract The use of first, second and third expanding seedling leaves of wheat (L1, L2 and L3 respectively), inoculated with conidial suspensions of Microdochium majus (syn. Microdochium nivale var. majus) in a detached leaf assay, for detecting components of partial disease resistance (PDR) was investigated across a range of wheat cultivars. Incubation periods (period from inoculation to first appearance of symptoms; a dull grey,green water-soaked lesion) and latent periods (period from inoculation to the first appearance of sporodochia) were longest and lesions smallest on L3. The expression of PDR components on L2 was intermediate to those on L1 and L3. The longer latent periods on L3 typically occurred after leaf senescence contrasting with latent periods on L1 and L2 where sporulation most frequently occurred on relatively green leaf tissue. Cultivar differences in the first appearance of symptoms, incubation period, which occurred before any leaf senescence was observed, correlated significantly across all leaf positions. Similarly cultivar differences in latent period were correlated for L1 and L2. However, latent periods on L3, which were the least consistent between cultivars across experiments, were not correlated with those of L1 or L2 in any experiment. The results indicate that due to the delay in sporulation until after leaf senescence, observations on latent period in L3 are less representative of what occurs in the whole plant where infection of living tissue is of greatest interest. This work indicates that the selection of the first or second expanding leaf of wheat is optimal for the use in the detached leaf assay using M. majus for studying components of PDR. [source] Photosynthetic Responses of a Temperate Liana to Xylella fastidiosa Infection and Water StressJOURNAL OF PHYTOPATHOLOGY, Issue 1 2004A. J. McElrone Abstract Xylella fastidiosa is a xylem-limited bacterial plant pathogen that causes bacterial leaf scorch in its hosts. Our previous work showed that water stress enhances leaf scorch symptom severity and progression along the stem of a liana, Parthenocissus quinquefolia, infected by X. fastidiosa. This paper explores the photosynthetic gas exchange responses of P. quinquefolia, with the aim to elucidate mechanisms behind disease expression and its interaction with water stress. We used a 2 × 2-complete factorial design, repeated over two growing seasons, with high and low soil moisture levels and infected and non-infected plants. In both years, low soil moisture levels reduced leaf water potentials, net photosynthesis and stomatal conductance at all leaf positions, while X. fastidiosa -infection reduced these parameters at basally located leaves only. Intercellular CO2 concentrations were reduced in apical leaves, but increased at the most basal leaf location, implicating a non-stomatal reduction of photosynthesis in leaves showing the greatest disease development. This result was supported by measured reductions in photosynthetic rates of basal leaves at high CO2 concentrations, where stomatal limitation was eliminated. Repeated measurements over the summer of 2000 showed that the effects of water stress and infection were progressive over time, reaching their greatest extent in September. By reducing stomatal conductances at moderate levels of water stress, P. quinquefolia maintained relatively high leaf water potentials and delayed the onset of photosynthetic damage due to pathogen and drought-induced water stress. In addition, chlorophyll fluorescence measurements showed that P. quinquefolia has an efficient means of dissipating excess light energy that protects the photosynthetic machinery of leaves from irreversible photoinhibitory damage that may occur during stress-induced stomatal limitation of photosynthesis. However, severe stress induced by disease and drought eventually led to non-stomatal decreases in photosynthesis associated with leaf senescence. [source] Leaf vascular dimensions associated with freeze tolerance in bahiagrass (Paspalum notatum)ANNALS OF APPLIED BIOLOGY, Issue 2 2009J.W. Breman Abstract Foliage damage as a result of individual freeze events is a major limitation to the expansion of bahiagrass (Paspalum notatum) pastures and hay production in Southeastern USA. Greater tolerance to such freeze events would allow production deeper into the fall and winter and allow expansion of this species into colder regions. While it has been reported that small cells are more tolerant to freeze damage, this possibility has not been explored in bahiagrass. Specifically, the hypothesis was examined that xylem vessels with smaller diameter in the midrib of leaves are associated with freeze tolerance among bahiagrass genotypes. Vascular bundle diameter was also measured as a possible index of xylem cell size. A total of eight bahiagrass genotypes were eventually studied representing four freeze-sensitive and four freeze-tolerant lines. There was a clear distinction in xylem cell size between the freeze-sensitive and the freeze-tolerant lines. The freeze-tolerant genotypes had xylem element cells that were significantly smaller than the freeze-sensitive genotypes. Averaged across three leaf positions and all genotypes, the xylem element diameter for the freeze-sensitive lines was 222 ,m and for the freeze-tolerant lines was only 164 ,m. A similar difference was observed in overall vascular bundle diameter with freeze-sensitive lines having a mean of 1168 ,m and the freeze-tolerant lines a mean of 917 ,m. These results indicated that the diameter of the xylem cells in the vascular midrib of bahiagrass may be an important variable influencing the sensitivity among genotypes to freeze damage. [source] | ||||||||||