Hyperspectral reflectance data were used to detect internal infestations of Angoumois grain moth, Sitotroga ceralella (Olivier), in wheat kernels. Kernel reflectance was measured with a spectroradiometer over a wavelength range of 350–2500 nm. Kernel samples were selected randomly and scanned every 7 d after infestation to determine the ability of the hyperspectral reflectance data to discriminate between infested and uninfested kernels. Immature stages of S. ceralella inside wheat kernels can be detected through changes in moisture, starch, and chitin content of the kernel. By using the spectrally-derived moisture variable (Log[1/R972nm]-Log[1/R1032nm]) and starch variable (Log[1/R982nm]-Log[1/R1014nm]), it was possible to discriminate between infested and uninfested wheat kernels with 100% classification accuracy based on 90% confidence intervals. Significant differences in the spectral reflectance between the infested and uninfested kernels were due to changes in moisture and starch content in wheat kernels. Three of the four chitin variables showed slight discrimination between the infested and uninfested wheat kernels based on 90% confidence intervals with 63.9%, 68.8%, 66.7%, and 41.6% classification accuracy of the three variables (Log[1/R1130nm]-Log[1/R1670nm]), (Log[1/R1139nm ]-Log[1/R1320nm]), (Log[1/R1202nm]-Log[1/R1300nm]), and (Log[1/R2046nm]-Log[1/R2302nm]), respectively. Spectral reflectance changes as a function of wheat kernel position relative to the spectroradiometer sensor did not differ significantly (P > 0.10).
The chile pepper (Capsicum annuum) crop is affected by several pests, pathogens, and weeds including Verticillium dahliae, Meloidogyne incognita, spurred anoda (Anoda cristata), Wright groundcherry (Physalis acutifolia), and tall morningglory (Ipomoea purpurea). These weed species are unimpaired hosts to V. dahliae and M. incognita. Chile plants have been found co-infected with V. dahliae and M. incognita in commercial fields. Greenhouse studies were conducted to determine the relationships among V. dahliae, M. incognita, and each of the four aforementioned plant species. Plants were either non-inoculated or inoculated with V. dahliae, M. incognita, or V. dahliae plus M. incognita. Six weeks after inoculation, plant infection by V. dahliae, M. incognita reproduction, plant height and biomass were measured. Three relationships were identified: V. dahliae was recovered from 100% of all four inoculated plant species, irrespective of M. incognita treatment; V. dahliae and M. incognita enhanced or had no effect on weed biomass but were pathogenic to chile; and co-infection by V. dahliae had no effect on nematode reproduction in the first M. incognita generation on the crop or weeds. These biological relationships suggest that the competitive impact of the weeds may increase and pathogen diversity may be affected in infested fields, ultimately impacting the efficacy of our common IPM tools. Accepted for publication 17 July 2013. Published 20 September 2013.
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