Spectral and Thermal Responses of Peanut to Infection and Colonization with Athelia rolfsii

Soilborne fungal diseases, including southern stem rot (causal agent: Athelia rolfsii), are major constraints to peanut production worldwide. Scouting for disease via visual observation is time and labor intensive but sensor technologies are a promising tool for plant disease detection. Prior research has focused on foliar diseases, and few studies have applied sensor-based tools for early detection of soilborne diseases. This study characterized the temporal progress of spectral and thermal responses of peanut plants during infection and colonization with A. rolfsii under controlled environment. In greenhouse experiments, A. rolfsii-inoculated and mock-inoculated lateral stems of peanut were inspected daily for symptoms, and leaf spectral reflectance and temperature were measured using a handheld spectrometer and thermal camera, respectively. Following onset of visual disease symptoms, leaflets on inoculated stems had greater spectral reflectance in the visible region compared with those on mock-inoculated stems. Leaflets on the inoculated stems also had greater normalized leaf temperatures as compared with leaflets on mock-inoculated stems. Overall, results indicate that signatures of disease development can be detected during peanut infection and colonization with A. rolfsii using spectral reflectance and thermal imaging technologies, and spectral signatures of disease are more consistent and specific compared with thermal ones. Though only one peanut variety, one pathogen isolate, and one single measurement were assessed per evaluation date, temporal progress of spectral and thermal responses on a daily basis characterized in this study can be used to develop sensor-based methods to detect southern stem rot and other soilborne diseases ultimately in the field.[Graphic: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license

Phenotypic Differentiation of Two Morphologically Similar Aflatoxin-Producing Fungi from West Africa

Aflatoxins (AF) are hepatocarcinogenic metabolites produced by several Aspergillus species. Crop infection by these species results in aflatoxin contamination of cereals, nuts, and spices. Etiology of aflatoxin contamination is complicated by mixed infections of multiple species with similar morphology and aflatoxin profiles. The current study investigates variation in aflatoxin production between two morphologically similar species that co-exist in West Africa, A. aflatoxiformans and A. minisclerotigenes. Consistent distinctions in aflatoxin production during liquid fermentation were discovered between these species. The two species produced similar concentrations of AFB1 in defined media with either urea or ammonium as the sole nitrogen source. However, production of both AFB1 and AFG1 were inhibited (p < 0.001) for A. aflatoxiformans in a yeast extract medium with sucrose. Although production of AFG1 by both species was similar in urea, A. minisclerotigenes produced greater concentrations of AFG1 in ammonium (p = 0.039). Based on these differences, a reliable and convenient assay for differentiating the two species was designed. This assay will be useful for identifying specific etiologic agents of aflatoxin contamination episodes in West Africa and other regions where the two species are sympatric, especially when phylogenetic analyses based on multiple gene segments are not practical