A quantitative assay for Amaranthus palmeri identification.

BACKGROUND: Amaranthus palmeri recently has been brought into the Midwestern USA as a contaminant in Conservation Reserve Program seeding mixes. Rapid species screening is required to mitigate the risk of continued species movement. RESULTS: Markers were developed for A. palmeri-specific nucleotide polymorphisms in the internal transcribed spacer of the ribosomal coding region. A quantitative polymerase chain reaction (qPCR) assay successfully identified A. palmeri from single-plant samples, simulated mixed-plant samples and seed mixtures. CONCLUSION: A qPCR assay for distinguishing A. palmeri from 12 other Amaranthus spp. was developed and validated. The assay can consistently detect a single A. palmeri seed when present in a pool of 100 total Amaranthus spp. seeds. © 2017 Society of Chemical Industry.

Yield Loss Assessment of Barley Yellow Dwarf Disease on Spring Oat in Illinois.

The quantitative relationship between yield of spring oat cvs. Ogle and Noble and incidence of barley yellow dwarf (BYD) disease caused by barley yellow dwarf virus (BYDV-PAV-IL) was studied. Field plots were infested with Rhopalosiphum padi vectoring BYDV-PAV-IL. A linear critical point regression model was developed that related percentage of maximum yield to BYD incidence, assessed by estimating the percentage of plants with BYD symptoms at Feekes growth stage 10.5 in each plot. The model y = 96.9 - 0.45x (r2 = 0.53) best explained the relationship. Test weight was unaffected by BYD. Although Noble consistently sustained higher disease incidence than Ogle, covariate analysis indicated that the effect of BYD on yield was similar for both cultivars. Studies of random versus focus inoculation of Noble oat, designed to determine the importance of compensation in reducing yield loss associated with BYD, indicated that compensation did not play an important role.