Submitted to: Multicrop Aflatoxin and Fumonisin Elimination and Fungal Genomics Workshop-The Peanut Foundation
Publication Type: Abstract only
Publication Acceptance Date: 10/19/2004
Publication Date: 10/28/2004
Citation: Brown, R.L., Chen, Z.-Y., Menkir, A., Cleveland, T.E. 2004. Identification of aflatoxin-resistance and potential markers in maize breeding materials developed in West Africa. In: Proceedings of the Multicrop Aflatoxin and Fumonisin Elimination and Fungal Genomics Workshop, October 25-28, 2004, Sacramento, CA. p. 43. Interpretive Summary:
Technical Abstract: The breeding program at IITA had originally developed maize populations from crosses of U.S. aflatoxin-resistant inbred lines with IITA resistant lines. Populations formed had 75%, 50%, or 25% U.S. germplasm. A total of 65 S5 (~98% towards inbred development) lines extracted from 75% U.S. x 25% IITA germplasm and 63 S5 lines derived from 50% U.S. x 50% IITA germplasm with resistance to lowland leaf rust, leaf blight, and Curvularia leaf spot, were advanced to S6. Seed samples of the first 65 S5 lines were sent to the USDA-ARS laboratory in New Orleans (SRRC) and were screened for resistance to aflatoxin contamination using the laboratory-based kernel screening assay (KSA). Based on the results of KSA screening, nine inbred lines with significantly lower levels of aflatoxin production compared to their respective U.S. resistant recurrent parents and with good agronomic features were selected. Seed samples of these inbred lines were increased in Nigeria in the 2004 dry season (December-April) and sent to SRRC to confirm their resistance to aflatoxin production. Following confirmation of the levels of resistance of these lines, they will be candidates for release as sources of resistance genes to aflatoxin production. These lines are also being tested in the field in Nigeria under artificial inoculation with Aspergillus flavus to assess the consistency of their resistance across the different strains of A. flavus. The remaining 63 S6 lines will be sent to SRRC for KSA screening. Several near-isogenic pairs of lines, differing significantly in aflatoxin accumulation, were identified at SRRC among IITA temperate (75% U.S.) breeding materials. When kernel embryo proteins of near-isogenic pairs were subjected to proteome analysis, several resistance-associated proteins (RAPs), categorized as stress-related, and a putative regulatory protein were identified. This former discovery supports the results of an earlier study involving U.S. resistant lines. This may be an important discovery, since drought and high nighttime temperatures are known to greatly increase aflatoxin levels in corn kernels. Possession of unique or higher levels of the identified stress-proteins may put resistant lines in an advantageous position over susceptible ones in the ability to defend against pathogens while under stress. Kernel endosperm protein analyses of near isogenic lines are currently being completed. After corresponding genes are cloned, confirmation studies, such as RNAi gene silencing experiments, are being conducted to highlight the role RAPs play in kernel resistance to aflatoxin production. These investigations will aid in selecting the best molecular markers for use in breeding strategies and transformation protocols involving IITA-bred germplasm.