AN INHIBITION SOLID-PHASE RADIOIMMUNOASSAY FOR ASPERGILLUS REPENS IN STORED CORN (ZEA MAYS)
Abstract
The Aspergillus glaucus group species is a major cause of the deterioration of shelled corn in low moisture storage. Inhibition solid-phase radioimmunoassay (ISPRIA) was developed to measure the growth of A. repens, a member of the A. glaucus group. Rabbit antisera were produced by immunization with A. repens conidia or germlings. Fungal antigens in test samples bound antibodies in crude antisera in competition with the reference antigen adsorbed to microtiter plates. Bound IgG were detected with ('125)I-Protein A. Sample preparation was simple and rapid; the assay could be completed in one day. The detection limit was 0.25 ug dry weight of fungus, equivalent to 10 ug per g corn. The response was linear with the log of fungal dry weight from 100 ug to 0.25 or 5 ug, depending on the antiserum. The response was not affected by the presence of corn, which had produced unacceptable nonspecific binding in noncompetitive radioimmunoassays and enzyme-linked immunosorbent assays. Cross-reactivity was high for A. ruber and moderate for A. amstelodami, both members of the A. glaucus group. Penicillium cyclopium, A. restrictus, and Gibberella zeae cross-reacted at a low level with the antiserum to germlings but not with the antiserum to conidia. The reactivity of the six other fungal species tested was less than 10% that of A. repens. Dent corn was stored at 86% relative humidity and 26(DEGREES)C after rewetting to 17% moisture content and inoculation with A. repens conidia. The corn had little mechanical damage and preharvest fungal infection. The corn was indexed periodically by ISPRIA and eight other measures of fungal development and seed deterioration. ISPRIA values were highly correlated with days of storage, evolved CO(,2), and ergosterol content (r = 0.99, 0.99, and 0.96, respectively) and with decrease in seed germination and visible mold at 3x (r = 0.91 and 0.91). ISPRIA values were moderately correlated with visible mold at 10x, blue eye, number of fungal propagules, and kernel infection (r = 0.82, 0.80, 0.79, and 0.71). ISPRIA, ergosterol content, kernal infection, number of propagules, and CO(,2) revealed fungal growth at day 10, the first sampling date. Production of CO(,2) after 52 days was 18% more than predicted from Steele's equations.
Degree
Ph.D.
Subject Area
Plant pathology
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.