Study of multiplication of cucumber mosaic virus in susceptible and resistant Capsicum annuuum lines

A previous survey on pepper lines (Capsicum annuum L.) indicated that a susceptible cultivar, Yolo Wonder, reacted to cucumber mosaic virus (CMV) by producing a systemic yellow mosaic. By contrast, CMV caused no symptoms on lines Perennial and Vania. The virus is recoverable from the uninoculated leaves of Perennial, while in Vania CMV is restricted to the inoculated leaves. To interpret these phenomena, a comparative study on CMV multiplication rates, yield, specific infectivity and relative proportion of RNAs was made in the inoculated leaves of the three pepper varieties. The rate of CMV multiplication, as estimated by the double antibody sandwich form of enzyme-linked immu-nosorbent assay, was lower in Perennial than in Vania or Yolo Wonder. The yield of virus purified from Perennial was very low when compared with Vania or Yolo Wonder. The specific infectivity of the virus extracted from Perennial was less than that from Vania or Yolo Wonder. These results suggest that Perennial is resistant to CMV multiplication, while restriction of the virus in inoculated leaves of Vania is not due to the inhibition of the virus replication. However, polyacrylamide gel electrophoresis revealed that the RNA profiles of CMV purified from the three pepper lines were similar.     

Temporal patterns of citrus greasy spot‐induced defoliation of sweet orange cultivars in Brazil

Recôncavo Baiano is an area favourable for the occurrence of citrus greasy spot (CGS) (Mycosphaerella citri), but there has been no study of this pathosystem in Brazil. This work aimed to characterise the temporal patterns of CGS‐induced defoliation in sweet orange cultivars ‘Bahia’ (Washington Navel) and ‘Pêra’. Temperature, rainfall and relative humidity were recorded, as well as weekly defoliation (fallen leaves/canopy m² or m³). Considering the mean of fallen leaves per canopy m², and mean canopy area, the total annual defoliation was estimated to be around 32 000 leaves per plant for ‘Bahia’ and 18 500 for ‘Pêra’ sweet orange. Spectral density analysis showed that defoliation has a 5‐week‐long main cycle for both cultivars. The proportion of symptomatic fallen leaves was never below 0.97. The monthly number of fallen leaves per canopy area was positively correlated with the mean CGS incidence on leaves. Defoliation was significant, resulting in a low leaf density throughout the year. Many defoliation cycles and the very high proportion of symptomatic fallen leaves assure a constant inoculum supply. Based on these results, CGS cannot be considered a minor disease, at least in Recôncavo Baiano.     

Brown Spot of Rice is Affected by Photon Irradiance and Temperature

Brown spot, caused by Bipolaris oryzae, is one of the most destructive diseases in rice. In this study, the effect of photon irradiance and temperature on brown spot development was evaluated. The concentration of total soluble sugars (fructose, glucose and sucrose) in rice leaves was also evaluated. Rice plants of cv. ‘Oochikara’ were inoculated with B. oryzae and kept in a greenhouse [20 ± 2°C (night time) and 35 ± 2°C (day time), ≈ 1000 μmol photons/m²/s] or two different mist chambers (25 or 32 ± 2°C, ≈ 15 μmol photons/m²/s at the top canopy). Plants kept in a mist chamber at 32 ± 2°C, under low photon irradiance, showed reduced incubation period (IP) and increase in the rate of lesion expansion. Brown spot severity in rice leaves was 67.8% at 32 ± 2°C, 27.8% at 25 ± 2°C and 11.4% under greenhouse conditions. The highest brown spot severity was found on plants grown under low photon irradiance, in which soluble sugar concentrations were lowest, suggesting that disease development was boosted under these particular growing conditions. Based on the results of this study, a continuous high temperature and low photon irradiance, in the presence of high relative humidity, and low soluble sugars contribute to an increase in brown spot development.     

Rôle de L'éthylène dans L'Accumulation de Capsidiol et la Sensibilité a Phytophthora capsici chez le Piment Traite par un Eliciteur

Role of ethylene in both the synthesis of capsidiol and the susceptibility to Phytophthora capsici of pepper treated with an elicitor With inoculated plants, there is a strong increase of ethylene, specially with Phyo 636. But, with plants inoculated and treated with G5 15 the quantities of ethylene are less important than with those ones inoculated and untreated with G5 15. After contamination (and only in this case), there is capsidiol synthesis as well wit h treated plants as with untreated ones, and the quantities are not significantly different. Generally, the level of induced resistance is higher wit h Phyo 636 (genetically resistant) than with Yolo Wonder (genetically susceptible). The adjunction of ethylene precursor (ACC) to G5 15 elicitor increases induced resistance with Yolo Wonder but decreases with Phyo 636: the inverse effect is observed when using ethylene inhibitor (AVG). It is suggested that, in the interaction Pepper—Phytophthora capsia, neither ethylene production nor capsidiol synthesis can be considered as biochemical tracers of induced resistance.     

The Effects of Co-Infection by Sunn-Hemp Mosaic Virus (SHMV) and Fusarium oxysporum on the Growth of French Bean

In the seedlings of three cultivars of French bean (Phaseolus vulgaris), ‘Prince,’‘Masterpiece’ and ‘Pinto’, co-infection by Sunn-hemp mosaic virus (SHMV) with either of the vascular wilt pathogens, Fusarium oxysporum f. sp. phaseoh (Fop) or f. sp. tracbeiphilum (Fot) caused greater losses in total fresh weight and in leaf area compared with uninfected plants or plants infected singly with any one of these pathogens. Co-infection of a fourth cultivar (‘Canadian Wonder’) had no greater effects on growth reduction than single infection. The concentration of SHMV in the leaves of ‘Prince’ and to a greater extent in the leaves of ‘Masterpiece’ increased more after double infection than with infection by the virus alone. The nature and possible mechanisms of the pathogenic effects in French bean are discussed.     

Persistence of enterohaemorrhagic and nonpathogenic E. coli on spinach leaves and in rhizosphere soil*

Aims: Survival of Escherichia coli O157:H7 and nonpathogenic E. coli on spinach leaves and in organic soil while growing spinach in a growth chamber was investigated. Methods and Results: Spinach plants were maintained in the growth chamber at 20°C (14 h) and 18°C (10 h) settings at 60% relative humidity. Five separate inocula, each containing one strain of E. coli O157:H7 and one nonpathogenic E. coli isolate were applied to individual 4‐week‐old spinach plants (cultivar ‘Whale’) grown in sandy soil. Leaf and soil inocula consisted of 100 μl, in 5 μl droplets, on the upper side of leaves resulting in 6·5 log CFU plant^?1 and 1 ml in soil, resulting in 6·5 log CFU 200 g^?1 soil per plant. Four replicates of each plant shoot and soil sample per inoculum were analysed on day 1 and every 7 days for 28 days for E. coli O157:H7 and nonpathogenic E. coli (by MPN) and for heterotrophic plate counts (HPC). Escherichia coli O157:H7 was not detected on plant shoots after 7 days but did survive in soil for up to 28 days. Nonpathogenic E. coli survived up to 14 days on shoots and was detected at low concentrations for up to 28 days. In contrast, there were no significant differences in HPC from days 0 to 28 on plants, except one treatment on day 7. Conclusions: Escherichia coli O157:H7 persisted in soil for at least 28 days. Escherichia coli O157:H7 on spinach leaves survived for less than 14 days when co‐inoculated with nonpathogenic E. coli. There was no correlation between HPC and E. coli O157:H7 or nonpathogenic E. coli. Significance and Impact of the Study: The persistence of nonpathogenic E. coli isolates makes them possible candidates as surrogates for E. coli O157:H7 on spinach leaves in field trials.     

THE EFFECT OF NUTRIENT LIMITATION AND ITS INTERACTION WITH LIGHT UPON THE PRODUCTS OF PHOTOSYNTHESIS IN MERISMOPEDIA TENUISSIMA (CYANOPHYCEAE)1

The metabolic fate of photosynthetically-fixed CO₂ was determined by labeling samples of Merismopedia tenuissima Lemmerman for 30 min with NaH¹⁴CO₃ and analyzing its incorporation into low molecular weight compounds, polysaccharide and protein. In N- and P-sufficient cultures, relative incorporation into protein increased as the irradiance used during the labeling period was decreased to 20 μE · m^-2 s^-1. This pattern was found for cells grown at irradiances of either 20 or 180 μE · m^-2· s^-1, although incorporation into protein was greater in cultures grown at the higher irradiance. In N-limited continuous cultures, relative incorporation into protein was low, independent of growth rate, and the same for samples tested at 20 or 180 μE · m^-2· s^-1 irradiance. In contrast, ¹⁴C incorporation into protein by P-limited cultures increased as growth rate increased, and at relative growth rates greater than 0.25, the incorporation was greater at 20 than at 180 μE · m^-2· s^-1. However, the total RNA content and maximum photosynthetic rate of the cultures was the same at all growth rates tested. The interaction between nutrient concentration and light intensity was studied by growing-limited continuous cultures at the same dilution rate, but different irradiances. Relative incorporation into protein was highest in cultures grown at 20 μE · m^-2· s^-1, in which the relative growth rate was 0.4. These results suggest that photosynthetic carbon metabolism may respond to relative growth rate μ/μ_max rather than to growth rate directly.     

Rapid, reversible alterations in spinach thylakoid appression upon changes in light intensity

Changes in light quantity and quality cause structural changes within the thylakoid membrane; long‐term responses have been described for so‐called ‘sun’ and ‘shade’ leaves. Many leaves, however, experience changes in irradiance on a time scale of minutes due to self‐shading and sun flecks. In this study, mature, attached spinach leaves were grown at 300 µmol photons m^?2 s^?1 then rapidly switched to a different light treatment. The treatment irradiances were 10, 800 or 1500 µmol m^?2 s^?1 for 10 min, or 10 or 20 min of self‐shading (about 10 µmol m^?2 s^?1). Image analysis of transmission electron micrographs revealed that a 10 min switch to a lower light intensity increased grana size and number per chloroplast profile by 10–20%. Returning the leaves to 300 µmol m^?2 s^?1 for 10 min reversed the phenomenon. Chlorophyll fluorescence measurements of detached, intact leaves at 77 K were suggestive of a transition from state 2 to state 1 upon shading. Diurnal ultrastructural measurements of granal size and number did not reveal a significant net change in ultrastructure over the time scale of hours. It is concluded that spinach chloroplasts can alter the degree of thylakoid appression in response to irradiance changes on a time scale of minutes. These ultrastructural responses are caused by biochemical and biophysical adjustments within the thylakoid membrane that serve to maximize photosynthesis and minimize photo‐inhibition under rapidly fluctuating light environments.     

Effects of Relative Humidity on Carbon Isotope Fractionation in Plants

Four C₃ plants and a C₄ plant were grown from seeds at four levels (30, 45, 60, and 75 %) of relative humidity. All plants were subjected to a 16 h day, at 500 μE/m².s^?1 photon flux density. Mature leaves were analyzed for their carbon isotopic composition. Isotope fractionation decreased by up to 3 ‰ with decreasing relative humidity in all C₃ plants, while the opposite trend was observed in the C₄ plant. The observed shifts in both C₃ and C₄ plants are attributed to decreased stomatal conductance at low relative humidity, resulting in a smaller P_i.     

Estimation of the anatomical, stomatal and biochemical components of differences in photosynthesis and transpiration of wild-type and transgenic (expressing yeast-derived invertase targeted to the vacuole) tobacco leaves

Photosynthesis and transpiration rates of transgenic (expressing yeast-derived invertase targeted to the vacuole) tobacco (Nicotiana tabacum L.) leaves were, respectively, 50 and 70% of those of a wild type at 20°C, 350 cm³ m^?3 CO₂ concentration, 450 μmol (photons) m^?2 s^?1 of light intensity, and 70% relative air humidity. These differences could be attributed: (a) to changes in leaf anatomy and, consequently, to changes in gases diffusion between the cells' surfaces and the atmosphere; (b) to different stomatal apertures, and, for the photosynthesis rate, (c) to the altered CO₂ assimilation rate. Our objective was to estimate the relative contributions of these three sources of difference. Measurements on the wild-type and the transgenic leaf cross-sections gave values for the cell area index (CAI, cell area surface per unit of leaf area surface) of 15.91 and 13.97, respectively. The two-dimensional model 2DLEAF for leaf gas exchange was used to estimate quantitatively anatomical, stomatal and biochemical components of these differences. Transpiration rate was equal to 0.9 for the wild-type and to 0.63 mmol m^?2 s^?1 for the transgenic leaf: 24.0% of the difference (0.066 mmol m^?2 s^?1 was caused by the greater cell area surface in the wild-type leaf, and 66.0% was caused by a smaller stomatal aperture in the transgenic leaf. Photosynthetic rate was 3.10 and 1.55 μmol m^?2 s^?1 for the wild-type and transgenic leaves, respectively. Only 10.3% of this difference (0.16 μmol m^?2 s^?1) was caused by the difference in CAI, and the remaining 89.7% was caused by altered CO₂ assimilation rate.     

Manifestation et Mode de Conservation de Leveillula taurica, Agent de l'Oïdium de la Tomate au Maroc

Manifestation and conservation of Leveillula taurica on tomatoes in Morocco Powdery mildew of tomato, caused by Leveillula taurica, was considered a minor disease until 1978 when serious outbreaks occurred. These outbreaks coincided with periods of a draught and the introduction of new hybrids from Europe. The pathogen infects a variety of plants, including eleven cultivated and five wild species. Infections of tomato plants were obtained by isolates collected from cultivated plants (Cynara cardunculus, Cicerarietinum, Medicago sativa, Capsicum annuum, Tropaeolum majus) and wild species (Chenopodium ambrosioides, Sonchus asper, Oxalis cemua, Urtica urens).     

Pénétration et migration du 59Fe appliqué sur les feuilles de Maïs; effet du dimáthylsulfoxyde

The uptake and translocation of ⁵⁹Fe applied to leaves of Zea mays L. is studied with special reference to the effect of dimethylsulfoxide (DMSO). ⁵⁹Fe is deposited on corn leaves as droplets of solution of ferrous sulfate or ferric nitrate (1 mM. The uptake of ⁵⁹Fe is affected by the associated anion; the penetration is more important with the nitrate than with the sulfate. The translocation of ⁵⁹Fe from the treated part during 24 hours is very low in all the experiments. The exsorption of ⁵⁹Fe taken up, from the site of application in different solutions (FeSO⁴, 7H₂O; EDTA Na) concerns only a low percentage of ⁵⁹Fe present in the treated part. DMSO (0.5 and 1 %) increases the uptake but not the translocation of ⁵⁹Fe applied as sulfate; it seems to have no effect when iron is applied as nitrate. The increase during 24 hours reaches between 32 % and 53 % in seven experiments with sulfate. The effect also appears in an experiment conducted during four weeks, with several applications of ferrous sulfate during this time. This effect of DMSO is discussed: it is mainly explained by the great hygroscopicity of this solvent, therefore the effect would in part depend on the solubility of salts in concentrated DMSO and of the climatic conditions: relative humidity and temperature of the air.     

Replacement of nitrate by ammonium as the nitrogen source increases the salt sensitivity of pea plants. I. Ion concentrations in roots and leaves

Pea seedlings (Pisum sativum L. cv ‘Kleine Rheinlän-derin’) were grown hydroponically in solutions containing either nitrate (3 or 14 mol m⁻³) or ammonium (3 mol m⁻³) as the nitrogen source. Ammonium nutrition as such had no negative effect on plant biomass production, but drastically increased the sensitivity to moderate salinity (50 mol m⁻³ NaCl). The reasons for this effect are investigated here and in a subsequent paper. The appearance of visible symptoms of salt damage (wilting of marginal leaf areas followed by progressive necrosis) was paralleled by the development of several characteristic modifications in the solute and metabolite contents. Major changes were: (i) high salt (NaCl) accumulation in leaves; (ii) accumulation of ammonium (up to 20 mol m⁻³) and amino acids (up to 110 mol m⁻³) in leaves, but at decreased ammonium uptake rates; and (iii) decreased protein content. In a comparison paper we report on the subcellular distribution of salts, ammonium and metabolites under the above conditions.     

Growth of Pseudomonas phaseolicola in susceptible and in resistant bean plants

Race 1 of Pseudomonas phaseolicola introduced into leaves of susceptible Canadian Wonder bean plants multiplied logarithmically for 3–5 days, reaching final populations about 10⁵–10⁶ times the original. In resistant Red Mexican, Race 1 multiplied less rapidly to give final populations about 10²–10³ times the original. Race 2 behaved in susceptible Red Mexican as did Race 1 in Canadian Wonder. Macroscopic symptoms appeared in leaves when bacterial numbers reached their maxima. When introduced into the cotyledonary node Race 1 moved more rapidly upwards than downwards, and more rapidly and farther in Canadian Wonder than in Red Mexican. But even in Canadian Wonder the bacterium appeared only sporadically above the node of the first compound leaf. It could be isolated only rarely from chlorotic haloes around necrotic areas in leaves, or from chlorotic leaves not carrying lesions. Fewer lesions developed and the bacteria multiplied less in older than in younger leaves. Addition of glucose and casein hydrolysate to inocula of Race 1, separately or together, had little effect on growth in Canadian Wonder or Red Mexican, and the bacterium grew equally well in extracts of susceptible and of resistant plants. Preinoculation of leaves with an avirulent race reduced the number of lesions caused by a virulent race inoculated later, and also reduced growth of this race in leaves of a susceptible variety.     

Antiphytovirale Aktivität von Rhamnolipid aus Pseudomonas aeruginosa

A rhamnolipid released by Pseudomonas aeruginosa 196 Aa into the culture medium reduced the number of local lesions induced by tobacco mosaic virus on leaves of the hypersensitive host Nicotiana glutinosa L. by up to 90%. The content of potato virus X in the systemically infected host Nicotiana tabacum L. ‘Samsun’ is decreased in inoculated as well as in secondarily infected leaves by up to 50%. In a smaller degree red clover mottle virus is influenced in the systemic host Pisum sativumconvar.speciosum (Dierb.) Alef ‘Nadja’.     

Changes in photon flux can induce stomatal patchiness

Images of chlorophyll fluorescence were used to detect the occurrence of stomatal patchiness in leaves from eight species under variable photon flux conditions. Pronounced stomatal patchiness was induced within 5–10 min after PFD was changed from intermediate (～450 μmol quanta m^?2 s^?1) to low (～150 μmol quanta m^?2 s^?1) levels. This effect was completely reversible by returning PFD to intermediate levels. The pattern of heterogeneous fluorescence for each leaf was usually similar during repeated applications of medium and low PFD. In three species, stomatal patchiness could only be induced in slightly water-stressed plants. Leaves of more severely water-stressed Xanthium strumarium plants in low air humidity exhibited oscillations in fluorescence that corresponded with oscillatory changes in leaf diffusion conductance for water vapour. Stomatal patchiness was also induced by illuminating dark-adapted leaves with low PFD (below 200–300 μmol quanta m^?2 s^?1). Infiltration of leaves with distilled water showed that heterogeneous chlorophyll fluorescence was caused by changes in stomatal apertures.     

Leaf anatomy during leaf development of photoautotrophically <Emphasis Type="Italic">in vitro</Emphasis>-grown tobacco plants as affected by growth irradiance

Tobacco (Nicotiana tabacum L.) plants were cultured in vitro photoautotrophically at three levels of irradiance (PAR 400–700 nm): low (LI, 60 μmol m⁻² s⁻¹), middle (MI, 180 μmol m⁻² s⁻¹) and high (HI, 270 μmol m⁻² s⁻¹). Anatomy of the fourth leaf from bottom was followed during leaf development. In HI and MI plants, leaf area expansion started earlier as compared to LI plants, and both HI and MI plants developed some adaptations of sun species: leaves were thicker with higher proportion of palisade parenchyma to spongy parenchyma tissue. Furthermore, in HI and MI plants palisade and spongy parenchyma cells were larger and relative abundance of chloroplasts in parenchyma cells measured as chloroplasts cross-sectional area in the cell was lower than in LI plants. During leaf growth, chloroplasts crosssectional area in both palisade and spongy parenchyma cells in all treatments considerably decreased and finally it occupied only about 5 to 8 % of the cell cross-sectional area. Thus, leaf anatomy of photoautotrophically in vitro cultured plants showed a similar response to growth irradiance as in vivo grown plants, however, the formation of chloroplasts and therefore of photosynthetic apparatus was strongly impaired.     

Inoculum Density Relationships for Infection of Some Eastern US Forest Species by Phytophthora ramorum

Our objectives were to establish inoculum density relationships between P. ramorum and selected hosts using detached leaf and whole‐plant inoculations. Young plants and detached leaves of Quercus prinus (Chestnut oak), Q. rubra (Northern red oak), Acer rubrum (red maple), Kalmia latifolia (mountain laurel) and Rhododendron ‘Cunningham's White’ were dip‐inoculated with varying numbers of P. ramorum sporangia, and the total number of diseased and healthy leaves recorded following incubation at 20°C and 100% relative humidity. Calibration threshold estimates for obtaining 50% infected leaves based on linear analysis ranged from 36 to 750 sporangia/ml for the five hosts. Half‐life (LD50) estimates (the number of spores for which the per cent of diseased leaves reaches 50% of its total) from asymptotic regression analysis ranged from 94 to 319 sporangia/ml. Statistically significant differences (P = 0.0076) were observed among hosts in per cent infection in response to increased inoculum density. Inoculum threshold estimates based on studies with detached leaves were comparable to those obtained using whole plants. The results provide estimates of inoculum levels necessary to cause disease on these five P. ramorum hosts and will be useful in disease prediction and for development of pest risk assessments.     

Differences in photosynthetic apparatus of leaves from different sides of the chestnut canopy

In crowns of chestnut trees the absorption of radiant energy is not homogeneous; leaves from the south (S) side are the most irradiated, but leaves from the east (E) and west (W) sides receive around 70 % and those from north (N) face less than 20 % of the S irradiation. Compared to the S leaves, those from the N side were 10 % smaller, their stomata density was 14 % smaller, and their laminae were 21 % thinner. N leaves had 0.63 g(Chl) m⁻², corresponding to 93 % of total chlorophyll (Chl) amount in leaves of S side. The ratios of Chl a/b were 2.9 and 3.1 and of Chl/carotenoids (Car) 5.2 and 4.8, respectively, in N and S leaves. Net photosynthetic rate (P _N) was 3.9 μmol(CO₂) m⁻² s⁻¹ in S leaves, in the E, W, and N leaves 81, 77, and 38 % of that value, respectively. Morning time (10:00 h) was the period of highest P _N in the whole crown, followed by 13:00 h (85 % of S) and 16:00 h with 59 %. Below 500 μmol m⁻² s⁻¹ of photosynthetic photon flux density (PPFD), N leaves produced the highest P _N, while at higher PPFD, the S leaves were most active. In addition, the fruits from S side were 10 % larger than those from the N side.     

Plant response and huanglongbing disease development against heat treatments on ‘Siam Purworejo’ (Citrus nobilis (Lour)) and ‘Nambangan’ (C. maxima (Burm.) Merr.) under field condition

Huanglongbing is known as a destructive disease in citrus production. Investigation on plant response and development of huanglongbing disease against heat treatment on ‘Siam Purworejo’ (Citrus nobilis (Lour)) and ‘Nambangan’ (C. maxima (Burm.) Merr.) was done. High-temperature treatment was applied by covering plants with an enclosed screen. The treatment plant has three types of CLas pathogen infection status. The result showed that heat treatments could significantly increase new flushes. It was found that intensity of HLB infected plant decreased. The treatments effect on the proline level was dependent on cultivar, leaves age and HLB-infection status. Chlorophyll content of HLB infected plants increased due to high temperature. High-temperature increased Fe content in the artificially infected plant, whereas Zn contents increased in the leaves of infected plants by vector. ‘Nambangan’ had higher Fe content than ‘Siam Purworejo’ on uncovered plants. CLas bacteria still persisted in infected plant based on real-time PCR analysis.