Differential Responses of Host and Non-host Substrata on Germination of Ascospores of Sclerotinia sclerotiorum

Effect of host.(Cicer arietinum L.) and some non-host (Allium cepa L., A. Sativum L., Ocimum sanictum L., Azadirachta indica Juss., Zingiber officinale Roscoe. And Curcuma longa L.) substrata on the germination of ascospores io Sclerotinia sclerotiorum (Lib.) de Bary has been observed. Maximum germination was noticed on flower petals of gram (C.arietinum) with minimum time (2.5 h) for germ tube initiation. Among the non-host substrate germination was completely inhibited on ginger rhizome peeling whereas delayed germination (after 12h) and lowest germination percentage (48%) as compared with other non-hosts, were observed on turmeric rhizome peeling. It is suggested that ginger extract may be effective in controlling stem rot and wilt of gram incited by S. sclerotiorum in the field.     

Deposition of Erysiphe graminis Conidia on a Barley Crop

Naturally released Erysiphe graminis conidia were trapped (on horizontal slides, on vertical sticky cylinders and in suction traps) in a barley crop infected with powdery mildew and the numbers of single spores and of clumps of different sizes deposited on the traps were counted. The efficiencies of impaction calculated from deposits and wind speed measurements were higher than expected from mean wind speed measurements. The values were consistent with the hypothesis that spores were removedpredominantly in gusts. More than half the conidia were removed in clumps of two or more spores. The measurements suggest that clumps were more effectively deposited than single spores. The measurements demonstrate that spore release mechanisms can influence spore deposition significantly, especially close to the source.     

Evaluation of Certain Cowpea Genotypes for Partial Resistance to Powdery Mildew (Erysiphe polygoni)

Partial resistance to powdery mildew (Erysiphe polygoni) in twenty one cowpea cultivars was assessed over two to three seasons under field conditions. Mildew incidence was recorded as number of leaflets affected/plant and severity as AUDPC or infection rate using Gompertz transformation. Irrespective of the parameter used to measure mildew resistance or the season, mean response of cvs V-105, V-269, V-276, V-282 and V-385 showed clear slow-mildewing, while RC-48, S-488, TVX-944-02E, V-27, V-36 and V-118 were rated as susceptible. Mildew resistance in some cultivars was negatively correlated with that for the leaf rust (Uromyces vignae). AUDPC was a more robust disease parameter than infection rate and showed a good correlation (r²= 0.79) with incidence.     

Germination of conidia of poppy powdery mildew (Erysiphe polygoni DC)

Mode of germination and effect of various substrates, temperature, humidities, light and darkness on germination of poppy powdery mildew conidia have been studied.Conidia germinated on all substrates tested. Highest germination (89.41 %) was on agar 2 %. Germination was equally good on dry slide and in water. Generally one, rarely two germ tubes emerged from each conidium from the corner or occasionally from other places. Germination started after two hours of incubation and was almost over in 5 hours. Germination energy was 86.2.Maximum temperature for germination was 32.5 C. Optimum lied near 20 C.Light and darkness did not affect germination.Conidia germinated at all relative humidities tested including 0 and 100 %.Department of Plant Pathology, Agricultural Experiment Station, University of Udaipur, Udaipur, India.Based on a part of Ph.D. thesis of the senior author.     

Evidence for Resistance-inducing Compounds in Conidia of Erysiphe graminis f.sp. hordei

Preparations of Erysiphe graminis f.sp. hordei conidia were spray-applied to the first leaf of barley plants which were subsequently challenge inoculated with virulent powdery mildew. The powdery mildew reducing effect of the preparations was assessed by scoring the outcome of the challenge inoculation. Homogenates of ungerminated conidia, germinated conidia, and methanol-water extracts of germinated conidia reduced the number of powdery mildew colonies. Cell wall fragments from ungerminated conidia, germinated conidia, and conidial germination fluid obtained from conidia germinated in aqueous suspension did not reduce the number of powdery mildew colonies. Microsconical analysis of the infection course following challenge inoculation indicated that the powdery mildew reducing effect is due partly to induced resistance.     

Distinct Innate Immune Phagocyte Responses to Aspergillus fumigatus Conidia and Hyphae in Zebrafish Larvae

Aspergillus fumigatus is the most common filamentous fungal pathogen of immunocompromised hosts, resulting in invasive aspergillosis (IA) and high mortality rates. Innate immunity is known to be the predominant host defense against A. fumigatus; however, innate phagocyte responses to A. fumigatus in an intact host and their contributions to host survival remain unclear. Here, we describe a larval zebrafish A. fumigatus infection model amenable to real-time imaging of host-fungal interactions in live animals. Following infection with A. fumigatus, innate phagocyte populations exhibit clear preferences for different fungal morphologies: macrophages rapidly phagocytose conidia and form aggregates around hyphae, while the neutrophil response is dependent upon the presence of hyphae. Depletion of macrophages rendered host larvae susceptible to invasive disease. Moreover, a zebrafish model of human leukocyte adhesion deficiency with impaired neutrophil function also resulted in invasive disease and impaired host survival. In contrast, macrophage-deficient but not neutrophil-deficient larvae exhibited attenuated disease following challenge with a less virulent (ΔlaeA) strain of A. fumigatus, which has defects in secondary metabolite production. Taking these results together, we have established a new vertebrate model for studying innate immune responses to A. fumigatus that reveals distinct roles for neutrophils and macrophages in mediating host defense against IA.     

The Effects of Temperature on the Incubation and Latent Periods of Powdery Mildew (Erysiphe polygoni) on Clematis

The effects of temperature on the length of the incubation and latent periods of clematis powdery mildew, caused by Erysiphe polygoni , were studied. At constant temperatures over the range of 10–29°C, the length of the incubation period ranged from 4 to 11 days, and the length of the latent period ranged from 4 to 13 days; no visible colonies developed at 30°C after 19 days. The relationship between temperature and the rates of fungal development within the incubation and latent periods (expressed as the reciprocal of the lengths of the incubation and latent periods) under constant temperature were described well by a non-linear model. The resulting curves were not the usual form of an asymmetrically bell-shaped type; instead, they were of exponential type with the development rate increasing with increasing temperatures. The relationship between temperature and the development rate during the post-incubation (before sporulation) period was non-linear with an optimum temperature of approximately 20°C.     

Deposition of Erysiphe graminis Conidia on a Barley Crop II. Consequences for Spore Dispersal

Measured deposition rates of Erysiphe graminis conidia are often greater than those calculated from spore fall speed, v^s, and mean wind speed. The predictions of two gradient transfer models of spore dispersal in crops, in which sedimentation and inertial impaction were calculated from v^s and local wind speed or estimated from measured values (Mc Cartney and Bainbridge 1987), were compared. Comparisons of the models suggest that deposition rates close to the source may be underestimated by a factor of two and deposition half distances may be doubled when deposition is calculated conventionally. The results illustrate the importance of accurately describing deposition processes when constructing spore dispersal models.     

Hydrolytic Enzymes of Ungerminated and Germinated Conidia of Erysiphe graminis DC f. sp. hordei Marchal

Activities of hydrolytic enzymes (esterase, lipase, phosphatase, protease, 1,3-β-glucanase, chitinase and amylase) were demonstrated in washings and extracts of ungerminated and germinated conidia of Erysiphe graminis f. sp. hordei , Marchal. No cellulase and only very little xylanase activity was detected. Considerable amounts, 65% of total conidia proteins can be extracted by shaking the conidia when the extraction medium contained non-ionic detergent only. Different extraction procedures were used to determine enzyme distribution between exo- and endoconidial compartments and to evaluate the enzyme extraction efficiency from conidia.
The possible physiological roles of the hydrolytic enzymes in the ungerminated as well as in the germinated conidia were discussed.     

Inheritance of powdery mildew (Erysiphe polygoni DC) resistance in mungbean (Vigna radiata L. Wilczek)

Detached mungbean (Vigna radiata L.Wilczek) leaves were inoculated with a conidial suspension of a local isolate (TI-1) of the powdery mildew pathogen (Erysiphe polygoni DC) under controlled environment conditions. Based on the latent period and severity of the infection, a rating scale of 0–5 was used to classify the host pathogen interactions. Reactions 0, 1 and 2 were considered resistant and referred to as R0, R1 and R2 while 3, 4 and 5 were classified as susceptible (S). RUM lines (resistant to powdery mildew) and their derivatives are crossed with several susceptible (reaction types 3–5) genotypes and the inheritance of the resistance was studied in the F₁, F₂ and F₃ generations. The results showed that powdery mildew resistance in mungbean is governed by two dominant genes designated as Pm-1 and Pm-2. When both Pm-1 and Pm-2 were present, an R0 reaction was observed after inoculation with TI-1. The resistant reaction was R1 when only Pm-1 was present and R2 in the presence of Pm-2. In the absence of both Pm-1 and Pm-2, susceptible reactions 3, 4 and 5 were observed.     

An observation on the influence of nitrogen fertilization on the attack of peas by powdery mildew (Erysiphe polygoni DC)

Summary A pot experiment with peas var. Pauli is described in which it was observed that plants fertilized with NH₄NO₃ were much less attacked by powdery mildew than those which did not receive any nitrogen.     

Differential Responses of Nitrogen-Fixing Cyanobacteria to Salinity and Osmotic Stresses

Two nitrogen-fixing Anabaena strains were found to be differentially tolerant to salinity and osmotic stresses. Anabaena torulosa, a brackish-water, salt-tolerant strain, was relatively osmosensitive. Anabaena sp. strain L-31, a freshwater, salt-sensitive strain, on the other hand, displayed significant osmotolerance. Salinity and osmotic stresses affected nitrogenase activity differently. Nitrogen fixation in both of the strains was severely inhibited by the ionic, but not by the osmotic, component of salinity stress. Such differential sensitivity of diazotrophy to salinity-osmotic stresses was observed irrespective of the inherent tolerance of the two strains to salt-osmotic stress. Exogenously added ammonium conferred significant protection against salinity stress but was ineffective against osmotic stress. Salinity and osmotic stresses also affected stress-induced gene expression differently. Synthesis of several proteins was repressed by salinity stress but not by equivalent or higher osmotic stress. Salinity and osmotic stresses induced many common proteins. In addition, unique salt stress- or osmotic stress-specific proteins were also induced in both strains, indicating differential regulation of protein synthesis by the two stresses. These data show that cyanobacterial sensitivity and responses to salinity and osmotic stresses are distinct, independent phenomena.     

紫外线A照射差异性损伤皮肤角质形成细胞和成纤维细胞

紫外线A(ultraviolet A,UVA)照射皮肤可产生红斑、色素沉着以及光敏性损伤,导致光老化甚至诱导皮肤癌。研究发现,UVA(320～400 nm)照射对皮肤角质形成细胞和成纤维细胞造成损伤的反应和损伤程度都有所不同。本文结合近年来的相关研究,对UVA照射导致的上述两种细胞的形态、细胞膜损伤、血红素氧合酶(heme oxygenase,HO)活性、HO-1表达、细胞内有害自由铁形成,以及其它抗氧化物水平的不同反应等进行阐述,总结分析了同等剂量UVA照射后对角质形成细胞和成纤维细胞损伤的差异性,这些分析可能为皮肤抗UVA照射损伤以及寻找新型防晒剂的开发提供新思路和实验依据。     

Differential Growth Responses of Marine Phytoplankton to Herbicide Glyphosate

Glyphosate is a globally popular herbicide to kill weeds and its wide applications may lead to accumulation in coastal oceans as a source of phosphorus (P) nutrient or growth inhibitor of phytoplankton. We studied the physiological effects of glyphosate on fourteen species representing five major coastal phytoplankton phyla (haptophyta, bacillariophyta, dinoflagellata, raphidophyta, and chlorophyta). Based on growth responses to different concentrations of glyphosate under contrasting dissolved inorganic phosphorus (DIP) conditions, we found that phytoplankton species could be classified into five groups. Group I (Emiliania huxleyi, Skeletonema costatum, Phaeodactylum tricornutum) could utilize glyphosate as sole P-source to support growth in axenic culture, but in the presence of DIP, they were inhibited by both 36-μM and 360-μM glyphosate. Group II (Karenia mikimotoi, Prorocentrum minimum, Dunaliella tertiolecta, Symbiodinium sp., Heterosigma akashiwo and Alexandrium catenella) could not utilize glyphosate as sole P-source to support growth, and in the presence of DIP growth was not affected by 36-μM but inhibited by 360-μM glyphosate. Glyphosate consistently enhanced growth of Group III (Isochrysis galbana) and inhibited Group IV (Thalassiosira weissflogii, Thalassiosira pseudonana and Chattonella marina) regardless of DIP condition. Group V (Amphidinium carterae) exhibited no measurable response to glyphosate regardless of DIP condition. This grouping is not congruent with the phylogenetic relationships of the phytoplankton species suggesting functional differentiation driven by environmental pressure. We conclude that glyphosate could be used as P-source by some species while is toxic to some other species and yet has no effects on others. The observed differential effects suggest that the continued use of glyphosate and increasing concentration of this herbicide in the coastal waters will likely exert significant impact on coastal marine phytoplankton community structure.     

Differential Responses of Crab Neuromuscular Synapses to Cesium Ion

Excitatory postsynaptic potentials (EPSP's) generated in crab muscle fibers by a single motor axon, differ in amplitude and facilitation. Some EPSP's are large at low frequencies of stimulation and show little facilitation; others are smaller and show pronounced facilitation. When K⁺ is replaced by Cs⁺ in the physiological solution, all EPSP's increase in amplitude, but small EPSP's increase proportionately more than large ones. Quantal content of transmission, determined by external recording at single synaptic regions, undergoes a much larger increase at facilitating synapses. The increase in quantal content of transmission is attributable to prolongation of the nerve terminal action potential in Cs⁺. After 1–2 h of Cs⁺ treatment, defacilitation of synaptic potentials occurs at synapses which initially showed facilitation. This indicates that Cs⁺ treatment drastically increases the fraction of the "immediately available" transmitter store released by each nerve impulse, especially at terminals with facilitating synapses. It is proposed that facilitating synapses normally release less of the "immediately available" store of transmitter than poorly facilitating synapses. Possible reasons for this difference in performance are discussed.