Submitted to: Book Chapter
Publication Type: Book / chapter
Publication Acceptance Date: 9/13/2007
Publication Date: 2/28/2008
Citation: Menkir, A., Brown, R.L., Bandyopadhyay, R., Chen, Z.-Y., Cleveland, T.E. 2008. Breeding Maize for Resistance to Mycotoxins at IITA. 2008. In: Leslie, J.F., Bandyopadhyay, R., Visconti, A., editors. Mycotoxins: Detection Methods, Management, Public Health, and Agricultural Trade. Chapter 23. Trowbrige, UK: Cromwell Press. p. 277-286. Interpretive Summary: Corn ear rot-causing fungi including Aspergillus and Fusarium are common in West and Central Africa and contaminate grain with mycotoxins that pose serious potential health hazards to humans in the region. In an effort to develop corn lines with resistance to aflatoxin contamination, seed were sent from the International Institute of Tropical Agriculture (IITA) to SRRC in 1998 for aflatoxin-resistance screening using the kernel screening assay (KSA). Among these lines, some showed levels of resistance to aflatoxin production as high or higher than the best U.S. lines. These encouraging results prompted the initiation of a breeding project between IITA and SRRC to combine resistance traits of the IITA lines with those of U.S. lines. Two populations were formed from crosses between U.S. and IITA lines: one with a 75% U.S. genetic background and another with a 50% U.S. and 50% IITA contribution. After four generations of selection and self-pollination, lines from these crosses were sent to SRRC for aflatoxin screening and several promising ones were identified. Pairs of lines with similar parental backgrounds but differing in aflatoxin levels were also identified and are being used for discovery of proteins and corresponding genes underlying resistance. Inbred lines with low aflatoxin levels will be confirmed through field trials in Nigeria. Other lines, screened for fumonisin accumulation by F. verticilloides showed low accumulation. New inbred lines with combined resistance to aflatoxin and fumonisin accumulation can be exploited as new sources of genes for breeding programs in the U.S. and Africa. This could provide growers and consumers with a safer crop and also increase profits.
Technical Abstract: Ear rot causing fungi including Aspergillus and Fusarium are common in maize in West and Central Africa. These fungi contaminate maize with mycotoxins that pose serious potential health hazards to humans in the sub-region. In an effort to develop maize germplasm with resistance to aflatoxin contamination, a collaborative germplasm screening work was initiated between IITA and USDA/ARS/SRRC in 1998. Among the IITA inbred lines screened in the laboratory, some had as high level as or higher level of resistance to aflatoxin production compared to the best USA lines. These encouraging results prompted the initiation of a breeding project to combine resistance factors of the IITA lines with resistance factors in the U.S. inbred lines. Several crosses and backcross populations were formed from selected resistant inbred lines from the USA and IITA. A total of 65 S5 lines were developed from the backcross populations and 144 S5 lines were derived from the F1 crosses. These lines were separated into groups and screened in SRRC laboratory using a kernel-screening assay. Significant differences in aflatoxin accumulation were detected among the lines within each group. Several promising S5 lines with aflatoxin values significantly lower than their respective U.S. resistant recurrent parent or their elite tropical inbred parent were selected for resistance-confirmation tests. We found pairs of S5 lines with 88% to 97% common genetic backgrounds differing significantly in aflatoxin accumulation. These pairs of lines are currently being used for proteome analysis to identify resistance-associated proteins and the corresponding genes underlying resistance to aflatoxin accumulation. Inbred lines with consistently low aflatoxin levels will be inoculated with A. flavus in the field in Nigeria to identify lines with cross-resistance to different strains. Our initial screening of 58 elite maize inbred lines using artificial field inoculation with F. verticilloids detected significant differences in fumonisin accumulation among the lines. Some inbred lines had less than or equal to 5 ppm fumonisin for two years at Ibaddan and for one year at Ikenne. The new inbred lines with combined resistance to aflatoxin accumulation from the temperate and tropical germplasm and the elite lines with low levels of fumonisin can be exploited as potentially new sources of genes in breeding programs to develop maize cultivars with resistance to mycotoxin contamination.