Description

Abstract: Under certain conditions Aspergillus flavus can infect plants and produce aflatoxin, one of the most highly carcinogenic natural substances known. An ongoing project seeks to reduce aflatoxin contamination of peanut (Arachis hypogae L.). This paper describes new research tools, which have been developed to reach this Goal. A minirhizotron system was used to study root growth and drought resistance in relation to aflatoxin resistance. The minirhizotron was combined with a microvideo camera, which has an ultraviolet light source to observe A. flavus infection using a strain of A. flavus that produces a green fluorescent protein (GFP). Fluorescence observed on roots, pods, and pegs decreased with time. Less than 5% of roots and pods observed with a minirhizotron fluoresced and less than 1% of pods or seeds cultured after harvest showed colonization by GFP A. flavus. Still, this technology provides an excellent tool for the study of infection pathways and A. flavus population development. To observe fluorescence at higher resolution, peanut was grown in 20-L containers in a growth chamber to which clear acrylic cuvettes filled with soil and inoculated with GFP A. flavus was attached. Although mycelia fluoresced on some pegs, A. flavus populations appeared small and levels of fluorescence were low. In a subsequent experiment using the same pod cuvette culture system, flowering plants was sprayed with A. flavus spores suspended in water. About 14 days after spraying the spore suspension on the flowers, A. flavus mycelia fluoresced on the surface of peanut flowers, but any fluorescence was observed in either excised ovules or in pegs excised before entering soil. Many minirhizotron images taken under ultraviolet illumination have little visible fluorescence. In order to quantify fluorescence and to detect fluorescence in images having weak fluorescence, software was developed, QuaCos, to analyze the red-green-blue color values of pixels in digital images. These tools, applied in combination, offer great potential to improve the understanding of how A. flavus attacks peanut, and how varieties and management methods might be developed to reduce risk of aflatoxin contamination.