Identification of Infection Pathways and Development of Inoculation Methods for Peanut Using Green-Fluorescence-Protein Aspergillus Flavus

摘要

Screening peanut (Arachis hypogea L.) germplasm for resistance to Aspergillus flavus was hampered by low and variable rates of infection. Three experiments were conducted to develop methods to inoculate Aspergillus flavus on peanut flowers, pegs and ovaries by strains of A. flavus, modified to produce a Green Fluorescence Protein (GFP). Maximum infection with GFP A. flavus was found by spraying an aqueous suspension of conidia over shoots and flowers of peanut which resulted in 100% infection of floral surfaces. Other methods tested included application of cracked corn inoculum to the surface of soil in cuvettes and mixing aqueous suspension or cracked corn inoculum with soil in cuvettes, designed to allow in situ observation of peg and pod development. Observations with an ultra violet-illuminated microscope showed fluorescence of GFP A. flavus on the surface of the peanut flowers and a fluorescing network of hyphae on ovules inside the peanut pegs before the pegs reached the soil surface. These experiments provide supporting evidence that A. flavus infection of peanut ovaries can occur during flowering or early peg formation.