Spot Fragments Research Articles

First Report of Leaf Spot on Sorghum bicolor Caused by Alternaria tenuissima in China

Sorghum bicolor (L.) is an important crop used in renewable fuels, which is widely planted in Africa, North America, and Asia for its resistance to stress (Dahlberg 2019). A foliar disease on sorghum was observed in 2019, affecting approximately 11,000 ha, in Daqing, Heilongjiang Province, China. Disease incidence averaged approximately 50% among all affected fields and caused 10 to 20% economic loss. At the initial stage of the infection, small brown spots with light yellow halos appeared on the leaves, which gradually enlarged and coalesced to form large areas of lesions, 2 to 20 mm long and 2 to 5 mm wide, on leaves in the advanced stage of the infection. To identify the pathogen, 10 symptomatic leaves were collected and surface disinfected with 1% sodium hypochlorite for 1 min followed by 70% ethanol for 30 s, rinsed in sterile distilled water, and dried on filter paper. Leaf spot fragments were then placed onto potato dextrose agar (PDA) and incubated at 28°C in darkness for 3 days. Four fungal isolates were obtained from the diseased leaves by a single-spore isolation method. The fungal colonies of the isolates had round margins with abundant, fluffy, and olive-green to brown aerial mycelia after 7 days on PDA. Conidiophores were pale brown with septa, straight or flexuous, single or in clusters, with branches forming occasionally. Numerous pale brown, obclavate to obpyriform shaped conidia were produced on conidiophores and occurred in long chains. Conidia ranged in size from 14.5 to 49.6 × 7.5 to 17.6 μm, with longitudinal and transverse septa varying from zero to three and from one to six, respectively (n = 50). Based on morphological characteristics, all the fungal isolates were preliminarily identified as Alternaria spp. (Simmons 2007). The internal transcribed spacer (ITS) region of rDNA and the partial coding sequences of allergen (Alt) and glyceraldehyde 3-phosphate dehydrogenase (G3PDH) genes of isolates were amplified and sequenced with primers ITS1/ITS4, Alt a/b, and G3PDH a/b, respectively (Woudenberg et al. 2013). DNA sequences from amplification of ITS from two isolates were deposited in GenBank (MN816298 and MN939684). BLAST analysis of the sequences from isolates AT1 and AT2 (MN816298 and MN939684) showed 99.64% (557/559 bp) and 100% (558/558 bp) similarity with the ITS sequence (MN907695) of Alternaria tenuissima (ZZ9-5-1). Sequences of Alt (MT109294) and G3PDH (MT109295) of isolate AT2 were 99.59% (486/488 bp) and 99.67% (596/598 bp) similar to the Alt and G3PDH sequences from A. tenuissima SY-4 (MK593137.1) and 15-238 (LC134315.1), respectively. Therefore, the pathogen was identified as A. tenuissima on the basis of the morphological characteristics and the sequences of ITS, Alt gene, and G3PDH gene. Pathogenicity of the isolates was tested on leaves of five sorghum seedlings by spraying with aqueous conidial suspensions (105 conidia/ml), whereas negative control plants were sprayed with sterile distilled water and then incubated in chambers at 25°C and 95% relative humidity. Plants inoculated with the fungus developed brown lesions on leaves within 8 days, whereas the negative controls were symptomless. To fulfill Koch’s postulates, reisolations from margins of necrotic leaf spot tissue of all tested strains were streaked on V8 agar (Blagojevic et al. 2015). Fungi isolated from lesions showed the same colony morphology as described above and were identified by morphological characters or DNA sequences as A. tenuissima. The control leaves remained asymptomatic, and the pathogen was not reisolated. The pathogenicity test was repeated with similar results. A. tenuissima could potentially cause leaf spots on many plants (Sun et al. 2019). However, this is the first report of A. tenuissima causing leaf spots on sorghum in China. Identification of this disease pathogen is important to prevent its spread to other areas.

Single shot all optical switching of intrinsic micron size magnetic domains of a Pt/Co/Pt ferromagnetic stack

We demonstrate that magnetization reversal in a ferromagnetic Pt/Co/Pt stack can be induced by a single femtosecond laser pulse. We find that the size of the switched spot is comparable to the size of the intrinsic magnetic domains. It requires an absorbed energy density of ∼4 mJ cm−2, beyond which the excited spot fragments into a multidomain structure. The switching process can be toggled with sequential laser pulses and is helicity-independent. Furthermore, the dynamics of the magnetization reversal occurs in a timescale less than one microsecond. These results suggest that all-optical switching in ferromagnetic films requires that the laser spot matches with the specific domain sizes.

NUMERICAL SIMULATIONS OF ACTIVE REGION SCALE FLUX EMERGENCE: FROM SPOT FORMATION TO DECAY

We present numerical simulations of active region scale flux emergence covering a time span of up to 6 days. Flux emergence is driven by a bottom boundary condition that advects a semi-torus of magnetic field with $1.7 \times 10^{22}$ Mx flux into the computational domain. The simulations show that, even in the absense of twist, the magnetic flux is able the rise through the upper $15.5$ Mm of the convection zone and emerge into the photosphere to form spots. We find that spot formation is sensitive to the persistence of upflows at the bottom boundary footpoints, i.e. a continuing upflow would prevent spot formation. In addition, the presence of a torus-aligned flow (such flow into the retrograde direction is expected from angular momentum conservation during the rise of flux ropes through the convection zone) leads to a significant asymmetry between the pair of spots, with the spot corresponding to the leading spot on the Sun being more axisymmetric and coherent, but also forming with a delay relative to the following spot. The spot formation phase transitions directly into a decay phase. Subsurface flows fragment the magnetic field and lead to intrusions of almost field free plasma underneath the photosphere. When such intrusions reach photospheric layers, the spot fragments. The time scale for spot decay is comparable to the longest convective time scales present in the simulation domain. We find that the dispersal of flux from a simulated spot in the first two days of the decay phase is consistent with self-similar decay by turbulent diffusion.

Heat and chemical stress modulate the expression of the α-RYR gene in broiler chickens

The biological cause of Pork Stress syndrome, which leads to PSE (pale, soft, exudative) meat, is excessive release of Ca(2+) ions, which is promoted by a genetic mutation in the ryanodine receptors (RyR) located in the sarcoplasmic reticulum of the skeletal muscle cells. We examined the relationship between the formation of PSE meat under halothane treatment and heat stress exposure in chicken alphaRYR hot spot fragments. Four test groups were compared: 1) birds slaughtered without any treatment, i.e., the control group (C); 2) birds slaughtered immediately after halothane treatment (H); 3) birds slaughtered immediately after heat stress treatment (HS), and 4) birds exposed to halothane and to heat stress (H+HS), before slaughtering. Breast muscle mRNA was extracted, amplified by RT-PCR, and sequenced. PSE meat was evaluated using color determination (L* value). The most common alteration was deletion of a single nucleotide, which generated a premature stop codon, resulting in the production of truncated proteins. The highest incidence of nonsense transcripts came with exposure to halothane; 80% of these abnormal transcripts were detected in H and H+HS groups. As a consequence, the incidence of abnormal meat was highest in the H+HS group (66%). In HS, H, and C groups, PSE meat developed in 60, 50, and 33% of the samples, respectively. Thus, halothane apparently modulates alphaRYR gene expression in this region, and synergically with exposure to heat stress, causes Avian Stress syndrome, resulting in PSE meat in broiler chickens.

Time and material dependence of the voltage noise generated by cathodic vacuum arcs

The high frequency fluctuations of the burning voltage of cathodic vacuum arcs have been investigated in order to extract information on cathode processes, especially concerning evolution in time after arc ignition. Eight cathode materials (W, Ta, Hf, Ti, Ni, Au, Sn, Bi) were selected covering a wide range of cohesive energy. The voltage noise was recorded using both a broad-band voltage divider and an attenuator connected to a fast oscilloscope (limits 1 GHz analog and 5 GS s−1 digital). Fast Fourier transform revealed a power spectrum that is linear in log–log presentation, with a slope of 1/f 2, where f is the frequency (brown noise). The amplitude of the spectral power of the voltage noise was found to scale with the cohesive energy, in agreement with earlier measurements at lower resolution. These basic results do not depend on the time after arc initiation. However, lower arc current in the beginning of the pulse shows greater voltage noise, suggesting an inverse relation between the noise amplitude and number of emission sites (cathode spot fragments).

Random and directed components of arc spot motion in vacuum

Sequences of photographic frames with resolution down to 10 ns and 2 μm pixel−1 were obtained for vacuum arcs (30–40 A) with and without external magnetic field (0.36 T). In both cases extensive statistical studies confirm the diffusion character of the motion of cathode spot fragments on 10 ns timescale. In addition to such a diffusion, the magnetic field provokes fragment steps of length ∼5 μm in the retrograde direction, approximately once in every 0.3 μs, which account for the directed spot movement in magnetic field. Thus two mechanisms are responsible for spot dynamics. Episodes of immobile spot fragments are also observed.

The X-ray radiation from cathode spot fragments in laser-induced vacuum discharges

The temporal evolution of X-ray emission of laser-induced discharges was investigated by means of a picosecond X-ray streak camera. Point-like structures with small divergence and thin hot layers of intense X-ray radiation with life time from 30 ps to 1.5 ns in a spectral range 100 eV-10 keV have been found in a comparatively low voltage vacuum discharge (U/spl ap/150 V-2.7 kV) initiated by picosecond laser beam. The radiation of laser induced breakdown was investigated just after breakdown as well as with a delay time (up to 20 ns) relative to the ignition point by the laser beam in order to eliminate the X-ray radiation coming from the laser-produced plasma.

The dynamics of arc cathode spots in vacuum. Part III: measurements with improved resolution and UV radiation

Arc cathode spots in vacuum with Cu cathodes have been registered by combining framing and streak channels of a fast image converter camera equipped with high-magnification optics. In a special version UV radiation could be used for imaging. In this way the internal fragment structure of the spots could be resolved down to values with exposure times of 10 ns. With light from the spectral range 200-800 nm the spot intensity is about ten times higher than when in the visible range 350-800 nm. The smallest observable fragment size is . It is demonstrated that the spot fragments can change their position within 10-50 ns, the corresponding velocities reaching . These positional changes are associated with splitting and merging of the fragments. Prior to splitting and after merging the fragments become very bright. Characteristic brightness peaks have been found in the nanosecond as well in the microsecond range. The average intervals between fluctuations or groups of fluctuations in each range amount to about 19 ns, 180 ns, and respectively. The fragment dynamics lead to random displacement of the spot as a whole. The streak pictures show this spot movement for times down to 100 ns. Within 100 ns, the spot velocity can reach about . Hence, spots and fragments are nanosecond phenomena. Apparent time constants of the fragments are explained by the nonlinear increase of the spot luminosity with increasing sojourn probability of the fragments in a given area. The effect leads to overestimating the phases of small displacements and of fragment merging when analysing time-integrated pictures.

Prevalence and Molecular Analysis of Two Hot Spots for Ectopic Recombination Leading to XX Maleness

Two hot spots of ectopic Xp-Yp recombination have previously been shown to be at the origin of XX maleness (Well et al., 1994, Nature Genet. 7:414-419). To get more insight into the molecular basis of the abnormal interchange, 25 Y(+) class 3 XX male patients were studied. The two hot spots were found to account for the aberrant exchange in more than 50% of the cases. In addition, there is a correlation between the prevalence of each hot spot and the degree of X-Y homology between the corresponding fragments. Sequencing of the X-Y junctions in six patiens, who carried a breakpoint mapping in either of these two hot spot fragments, showed that their precise lacations were different from one individual to the other. In particular, the results obtained here in four new patients exclude the possibility that the repeated elements, present in these X-Y homologous fragments, are responsible for the high incidence of X-Y interchanges observed. Moreover, the breakpoints of all 25 class 3 XX males were found to be arranged in the same order on the X and Y chromosomes. This suggests that most ectopic recombinations leading to class 3 XX maleness involve X-Y homologous sequences persisting from an ancestral larger block of homology on the short arms of both sex chromosomes.