2012 Annual Report
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.
The international Institute of Tropical Agriculture (IITA) in collaboration with USDA-ARS-Southern Regional Research Center (SRRC) in New Orleans, LA, has developed inbred (purely inherited from parents) lines from bi-parental crosses and backcross (crossed with one parent) populations containing temperate maize germplasm from the U.S.A. as sources of resistance genes. After several years of inbreeding with selection for agronomic performance (suitability to the environment), adaptive traits, and resistance to aflatoxin production, 50 advanced inbred were developed. Some of these lines were crossed with adapted inbred lines that have good levels of resistance to aflatoxin and fumonisin production to generate pedigree (a lineage) populations. The pedigree populations have been good sources of 80 S5 (5th generation of selfing) lines, which were sent along with the 50 advanced inbred lines to the USDA-ARS-SRRC laboratory in 2011 to evaluate their resistance to aflatoxin contamination using kernel screening assay (KSA). Of these, 29 advanced lines had aflatoxin values similar to or much lower than resistant control line MI82. All advanced inbred lines produced less aflatoxin compared to the susceptible check. Among the 80 S5 lines derived from bi-parental crosses involving aflatoxin and fumonisin resistant parental lines and evaluated using KSA, 54 S5 (self pollinated 5 times to create an inbred line) lines had similar or lower levels of aflatoxin in comparison to MI82. Most of these lines had aflatoxin value much lower than the susceptible check. The best aflatoxin resistant inbred lines selected from the advanced lines were crossed with drought tolerant lines to generate source populations for developing new inbred lines that combine drought tolerance with resistance to aflatoxin contamination. The selected best aflatoxin resistant advanced inbred lines were also used to develop single-cross hybrids (offspring of genetically unlike parents), which were evaluated in three independent trials at four locations in 2010. Seed samples harvested from the hybrids grown at two locations were evaluated for resistance to aflatoxin production using KSA. Eleven hybrids had at least 50% less aflatoxin contamination compared to the commercial hybrid check or control (Oba Super I). The selected best hybrids were also found to be competitive to the commercial hybrid check in grain yield and other agronomic traits including resistance to the major foliar diseases prevalent in the lowlands. Some of the advanced aflatoxin resistant inbred lines as well as the best S5 lines were planted during the 2011 dry season to generate hybrids for resting during the main growing season in 2011. Two independent trials composed of 38 yellow and 71 white single-cross hybrids of aflatoxin resistant lines along with commercial hybrid checks were evaluated at four test locations in Nigeria in 2011. Among the two sets of hybrids evaluated in these trials, only six hybrids produced grain yields which were significantly lower than the respective commercial hybrid check. Most of the selected hybrids were competitive to the commercial hybrid check in their yield potential and other agronomic traits including resistance to the major foliar diseases prevalent in the lowlands. The level of resistance to aflatoxin production of these hybrids harvested at two locations is currently being evaluated in the laboratory at IITA using a kernel-based screening assay.