Soybean diseases: Unique situations in Africa

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Soybean pests

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First report of Sclerotinia sclerotiorum causing stem rot on soybean (Glycine max) in Ethiopia

Open Access ArticleSclerotinia sclerotiorum causes a devastating disease on soybean (Sclerotinia stem rot) and attacks over 500 other hosts (Grau and Hartman 2015). In October 2018, research plots at Jimma Agricultural Research Center, Ethiopia, were evaluated for soybean diseases. A sample of 100 randomly selected plants of soybean line T44-15-T110-16SH1 were evaluated for Sclerotinia stem rot in a research plot that was 4 × 2.4 m with 60 cm between the four rows and 5 cm between plants within a row. All but 16 stems had stem rot symptoms with an average plant severity rating of 3.5 (SE = 0.18) based on an adapted 1 (1 to 10% of the stem affected) to 5 (91 to 100% of the stem affected) rating scale (Little and Hills 1978). Five infected stems were selected and sent to the USDA-ARS Soybean Disease and Pest Research Laboratory, Urbana, IL. Three sclerotia removed from each of three infected stems ranged from 4 to 18 mm long and 1 to 2 mm wide. Sclerotia were placed on potato dextrose agar (PDA) in 9.8-cm-diameter Petri plates and incubated at 24°C with a 16-h photoperiod for 4 days. The white, appressed mycelia grew from the sclerotia and covered the entire plate after 48 h, with sclerotia forming on the edge of the plate by 4 days. To confirm pathogenicity, a mycelial plug was removed from the margin of a 2-day-old colony of one of the isolates, was obtained by pressing the large end of a 200-μl pipette tip into the culture, and was placed on top of a cut stem above the second trifoliolate of four 3-week-old plants of soybean cultivar Williams 82. Plants were then incubated in a moist chamber for 48 h prior to being placed in a greenhouse held at 22°C with a 16-h photoperiod. Necrotic lesions and white mycelia appeared on the stems 4 days postinoculation. The pathogen was reisolated and cultured on PDA. After 4 days, the reisolated cultures with sclerotia appeared morphologically to be S. sclerotiorum

Magnetic Field Generation in Stars

Enormous progress has been made on observing stellar magnetism in stars from the main sequence through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence,in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Thus we maybe at the dawn of a new era of exciting discoveries in compact star magnetism driven by the opening of a new, non-electromagnetic observational window. We also review recent advances in the theory and computation of magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo theory. These advances offer insight into the action of stellar dynamos as well as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field generation in stars to appear in Space Science Reviews, Springe

Microarray‐Based Genetic Mapping Using Soybean Near‐Isogenic Lines and Generation of SNP Markers in the Rag1

A strategy using near-isogenic lines (NILs) and Affymetrix Soybean GeneChip microarrays was employed to identify genetic markers closely linked to the soybean aphid [ Matsumura (Hemiptera: Aphididae)] resistance gene in soybean [ (L.) Merr.]. Genomic DNA from the aphid-resistant cultivar Dowling and the aphid-susceptible cultivar Dwight was labeled and hybridized to arrays, identifying more than 1500 putative single feature polymorphisms (SFPs) between these genotypes. To find polymorphisms closely linked to the aphid-resistance locus, genomic DNA samples from two NILs developed through backcrossing from Dowling four times to Dwight were also hybridized. Comparison of hybridization signals between the NILs and the recurrent parent identified more than 70 SFPs in each NIL between the NIL and the recurrent parent genotype. There were 22 SFPs shared by both NILs, representing molecular markers putatively linked to . Four selected SFPs were converted to SNP markers and confirmed by conventional genetic mapping to be closely linked to . The technique that we describe can be used to identify polymorphisms in a genetic region of interest and generate molecular markers closely linked to an agronomically important trait using a suitable oligonucleotide microarray