Spectral-based screening approach evaluating two specific maize lines with divergent resistance to invasion by aflatoxigenic fungi

Authors: HRUSKA, ZUZANA - Mississippi State University; YAO, HAIBO - Mississippi State University; KINCAID, RUSSELL - Mississippi State University; TAO, FEIFEI - Mississippi State University; BROWN, ROBERT - Retired ARS Employee; CLEVELAND, ED - Retired ARS Employee; Rajasekaran, Kanniah - Rajah; Bhatnagar, Deepak

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2019
Publication Date: 1/22/2020
Citation: Hruska, Z., Yao, H., Kincaid, R., Tao, F., Brown, R.L., Cleveland, T.E., Rajasekaran, K., Bhatnagar, D. 2020. Spectral-based screening approach evaluating two specific maize lines with divergent resistance to invasion by aflatoxigenic fungi. Frontiers in Microbiology. 10:3152. https://doi.org/10.3389/fmicb.2019.03152.
DOI: https://doi.org/10.3389/fmicb.2019.03152

Interpretive Summary: Corn kernels infected with the fungus Aspergillus flavus are often contaminated with carcinogenic toxins called aflatoxins. Aflatoxin contamination can occur in the field or under improper storage conditions. Some corn varieties can tolerate fungal infection compared to other varieties. Detection of fungal infection and toxin contamination is often a laborious procedure and invariably results in sample destruction. Identification and measurement of fungal infection with toxin producing strains and aflatoxin contamination in resistant ans susceptible corn hybrids is explored in this manuscript by imaging corn kernels for unique fluorescence spectral signatures emitted from infected kernels. The fluorescence hyperspectral signatures were also compared with the kernels infected with a non-toxin producing fungal strain for comparison. This study provides a viable and practical means of earliest detection of aflatoxins with hyperspectral fluorescence thus enabling food safety. Growers, scientists, grain/food industry professionals, and export/import officials will greatly benefit from this technology.

Technical Abstract: In an effort to control aflatoxin contamination in food and/or feed grains, a segment of research has focused on host resistance to eliminate aflatoxin from susceptible crops, including maize. To this end, screening tools are key to identifying resistant maize genotypes. The traditional field screening techniques, the kernel screening laboratory assay (KSA), and analytical methods (e.g. ELISA) used for evaluating corn lines for resistance to fungal invasion, all ultimately require sample destruction. A technologically advanced take on the basic BGYF presumptive screening test, fluorescence hyperspectral imaging offers an option for nondestructive and rapid image-based screening. The present study aimed to differentiate fluorescence spectral signatures of representative resistant and susceptible corn hybrids infected by a toxigenic (SRRC-AF13) and an atoxigenic (SRRC-AF36) strain of Aspergillus flavus, at several time points (5, 7, 10 and 14 days), in order to evaluate fluorescence hyperspectral imaging as a viable technique for early, non-invasive aflatoxin screening in resistant and susceptible corn lines. The study utilized the KSA to promote fungal growth and aflatoxin production in corn kernels inoculated under laboratory conditions and to provide actual aflatoxin values to relate with the imaging data. Each time point consisted of 78 kernels divided into four groups (30-susceptible, 30-resistant, 9-susceptible control, and 9-resistant control), per inoculum. On specified days, kernels were removed from the incubator and dried at 60 oC to terminate fungal growth. Dry kernels were imaged with a VNIR hyperspectral sensor (image spectral range of 400-1000 nm), under UV excitation centered at 365 nm. Following imaging, kernels were submitted for the chemical AflaTest assay (VICAM). Fluorescence emissions were compared for all samples over 14 days. Analysis of strain differences separating the fluorescence emission peaks of resistant from the susceptible strain indicated a main effect of strain (p<0.01) where the emission peaks of the resistant strain and the susceptible strains differed significantly from each other, and there was a significant difference in fluorescence intensity between the treated and control kernels of both strains. These results indicate a viable role of fluorescence hyperspectral imaging for non-invasive screening of maize lines with divergent resistance to invasion by aflatoxigenic fungi.