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.
After several years of inbreeding with selection for agronomic performance, adaptive traits, and resistance to aflatoxin production, 50 advanced inbred lines, (lines bred to exclude genetic variation for each trait) have been developed. These advanced lines were sent to the Southern Regional Research Center (SRRC) in 2010 for kernel screening assay (KSA). Twenty-nine of 50 advanced lines had aflatoxin values similar to or much lower than the resistant control; all 50 produced less aflatoxin than the susceptible check (a control against which the developed lines are compared). Some of the aflatoxin-resistant inbred lines were selected for crossing with aflatoxin-resistant adapted tropical maize inbred lines to generate new source populations. Some of the advanced aflatoxin-resistant inbred lines were also crossed to fumonisin-resistant tropical inbred lines to develop source populations for developing inbred lines with combined resistance to aflatoxin and fumonisin. The 101 S5 (selfed and selected for 5 generations) lines derived from these crosses were evaluated at two locations in Nigeria in 2010. Furthermore, 69 S6 lines with good synchrony between pollen shed and silking, desirable agronomic traits, and resistance to foliar diseases were selected for further testing in hybrid combinations in 2011. The 101 S5 lines were also sent to SRRC laboratory in 2010 for KSA aflatoxin-screening. Results showed that 54 of the 80 S5 lines screened had similar or lower levels of aflatoxin compared to the resistant check; most had values much lower than the susceptible check. Two trials composed of 36 yellow and 20 white hybrids formed from lines selected for resistance to aflatoxin production using the KSA were evaluated at three locations in Nigeria in 2009. Seeds harvested from these trials were screened for resistance to aflatoxin production in 2010. Most of the selected best yellow hybrids had less than 20 parts per billion (ppb) aflatoxin under natural infection when they were planted under both full irrigation and induced drought stress. Also, the 20 best yellow hybrids had 50% to 100% less aflatoxin contamination in comparison to a commercial hybrid (Oba Super. 2)check when screened using the KSA. These hybrids were found to be similar to or better than a common commercial hybrid, Oba Super 2, in other desirable agronomic traits and resistance to foliar diseases. In the white hybrid trial, ten of the best 15 hybrids had less than 20 ppb aflatoxin under natural infection when they were planted both under full irrigation and induced drought stress. Also, the 15 best hybrids had greater than 50% less aflatoxin contamination in comparison to a commercial hybrid (Oba 98) check when screened using the KSA. These hybrids were found to be competitive to the commercial hybrids in grain yield and other adaptive traits. All of the above-efforts advance our objective of developing aflatoxin-resistant corn inbreds for use in Africa and the United States. Research progress was monitored through teleconferencing, frequent email communications and reports.