1a.Objectives (from AD-416):
Goals are to develop and evaluate corn inbreds demonstrating resistance to aflatoxin contamination in the U.S. and Africa, and to identify biochemical markers in these inbreds useful in marker-assisted breeding.
1b.Approach (from AD-416):
Inbreds will be developed through breeding at International Institute of Tropical Agriculture (IITA) Ibadan, Nigeria, West Africa. They will then be selected based on agronomic traits and foliar and ear rot resistance(s) and sent to the U.S. for evaluation for resistance to aflatoxin contamination using the rapid kernel screening assay (KSA). Information obtained through these screenings will be used to select lines to advance, through breeding, to the next generation. The KSA will also be used to idetify near-isogenic lines differing in aflatoxin accumulation among the breeding materials. Proteomics and microarry analysis will performed on these lines to identify proteins and corresponding genes associated with resistance. Information obtained will be used to develop markers for use in marker-assisted breeding. Resistance will be confirmed in all lines under natural conditions of high disease pressure in Nigeria. Promising germplasm will be released for use in U.S. breeding programs and national programs in Central and West Africa.
Initially, tropical and sub-tropical maize inbred lines developed at International Institute of Tropical Agriculture (IITA) were screened at Southern Regional Research Center (SRRC) laboratory using the kernel-based screening assay (KSA) and some lines with high levels of resistance to aflatoxin production were identified. The selected tropical lines were used as recurrent parents (parents that are crossed with the first and subsequent generations) to develop backcrosses (crossing of a hybrid with one of its parents) with temperate maize inbred lines (progeny from mating parents who are closely related genetically) as good sources of resistance to aflatoxin accumulation. Several early generation lines were derived from the backcross populations and evaluated for desirable agronomic traits (ability of plants to perform under different environmental conditions), resistance to the major foliar diseases and ear rots at two locations in Nigeria. Promising S3 (third generation through selfing) lines were selected and planted during the dry season to develop S4 (fourth generation through selfing) lines for further evaluation and inbreeding during the main cropping season. The best S4 lines with desirable agronomic traits were again selected and planted during the dry season to produce enough quantity of seeds for screening in the SRRC laboratory using KSA. Significant differences in aflatoxin production were detected among the S5 (fifth generation through selfing) lines evaluated in different groups. Among these, several S5 lines accumulating significantly lower levels of aflatoxin than their respective recurrent parent were selected to form hybrids (offspring of two genetically distinct parents) for testing in multiple locations and to conduct resistance-confirmation tests. The results of various trials conducted in multiple locations identified some hybrids that accumulated 100% to 150% less aflatoxin in comparison with the commercial hybrids. Also, these hybrids were as high yielding as or higher yielding than the commercial hybrids and had desirable agronomic traits. To further boost the yield potential and resistance to aflatoxin contamination in maize hybrids, several crosses have been made between parents with complementary traits to combine tolerance to drought with resistance to the major foliar diseases and aflatoxin accumulation in the new generation of maize inbred lines. The resulting new maize inbred lines which are being further tested, may be used directly as parents and as good sources of novel genes by the national maize breeding programs to develop high yielding maize hybrids with resistance to aflatoxin contamination and tolerance to drought stress.