Use of Two Pathogen-inhibiting Streptomyces Isolates for Biocontrol of Scab Disease of Raphanus sativus

Streptomyces species are ubiquitous soil bacteria that are promising as biological control agents due to their prolific antibiotic production that can inhibit soil-borne plant pathogens. This includes Streptomyces scabies, which causes scab disease on underground storage organs. The goal of this research was to test two Streptomyces isolates that have known inhibitory and biocontrol abilities against S. scabies in a potato (Solanum tuberosum) agricultural system for their effectiveness in biocontrol of this pathogen in a radish (Raphanus sativus) greenhouse assay. Pathogenic S. scabies were mixed into either pasteurized or unpasteurized soil prior to planting. Radish seeds or radish roots were soaked in a spore suspension of the two biocontrol Streptomyces isolates. Controls of treatments without the pathogen and the biocontrol Streptomyces were included. Radish plants were grown to maturity. Upon harvesting, the radish taproot was rated for scab disease and tuber weight and length were determined. Disease levels were reduced in the presence of the two biocontrol Streptomyces. Taproot weight was greater in the treatments that included the biocontrol Streptomyces. In addition, evidence was sought to determine the ability of these Streptomyces isolates and other pathogen-inhibiting bacteria to enter into an endophytic relationship with the radish plant. For this, several protocols were assessed to try to optimize the isolation of endophytic bacteria from stem and taproot tissue. Surface-sterilized tissue sections (stem and taproot) or macerated stem tissue spread on agar plates have indicated the presence of several bacterial endophytes, including two putative Streptomycete isolates from the stem tissue sections. The search for additional endophytic bacteria capable of inhibiting the scab pathogen are currently underway. The results of this study are promising for the use of these Streptomyces isolates for biocontrol against scab disease in radish

Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54

We report on Chandra X-ray Observatory (CXO) observations of the pulsar wind nebula (PWN) associated with PSR B0355+54 (eight observations with a 395 ks total exposure, performed over an 8 month period). We investigated the spatial and spectral properties of the emission coincident with the pulsar, compact nebula (CN), and extended tail. We find that the CN morphology can be interpreted in a way that suggests a small angle between the pulsar spin axis and our line-of-sight, as inferred from the radio data. On larger scales, emission from the 7' (2 pc) tail is clearly seen. We also found hints of two faint extensions nearly orthogonal to the direction of the pulsar's proper motion. The spectrum extracted at the pulsar position can be described with an absorbed power-law + blackbody model. The nonthermal component can be attributed to magnetospheric emission, while the thermal component can be attributed to emission from either a hot spot (e.g., a polar cap) or the entire neutron star surface. Surprisingly, the spectrum of the tail shows only a slight hint of cooling with increasing distance from the pulsar. This implies either a low magnetic field with fast flow speed, or particle re-acceleration within the tail. We estimate physical properties of the PWN and compare the morphologies of the CN and the extended tail with those of other bow shock PWNe observed with long CXO exposures.Comment: 11 pages, 8 figure

PSR J1709-4429's proper motion and its relationship to SNR G343.1-2.3

We have obtained a deep (670 ks) CXO ACIS image of the remarkable pulsar wind nebula (PWN) of PSR J1709 -4429, in four epochs during 2018-2019. Comparison with an archival 2004 data set provides a pulsar proper motion μ=13 ± 3 mas yr-1at a PA of 86° ± 9° (1σ combined statistical and systematic uncertainties), precluding birth near the center of SNR G343.1-2.3. At the pulsar's characteristic age of 17 kyr, the association can be preserved through a combination of progenitor wind, birth kick, and PWN outflow. Associated TeV emission may, however, indicate an explosion in an earlier supernova. Inter-epoch comparison of the X-ray images shows that the PWN is dynamic, but we are unable to conclusively measure flow speeds from blob motion. The pulsar has generated a radio/X-ray wind bubble, and we argue that the PWN's long narrow jets are swept back by shocked pulsar wind venting from this cavity. These jets may trace the polar magnetic field lines of the PWN flow, an interesting challenge for numerical modeling