(MP420 x 4001 x MP420)-3-1-2-2-B

43 fg

aMeans followed by the same letter are not significantly different based on the least significant difference test (p = 0.05).

aMeans followed by the same letter are not significantly different based on the least significant difference test (p = 0.05).

(Babangoyo, KU1414-SR, 1368, 4001, and 9450) were crossed to three or four selected genotypes from the United States (B73xTex6, C12, GT-MAS:gk, MI82, MO 17xTex6, MP420, OH516, and T115) that accumulated low levels of aflatoxin (Brown et al., 1995) to form 16 Fj crosses. Each F1 cross was crossed with the parental genotype from the United States as a recurrent parent to generate 16 backcross (BC1) populations. In addition, seven elite IITA inbred lines (Babangoyo, KU1414-SR, 1368, 4001, 5012, 9071, and 9450) were crossed to two or three of the same set of US genotypes to develop 16 F1 crosses.

Measuring the amount of aflatoxin produced by A. flavus in maize is both tedious and expensive, so we could not evaluate aflatoxin production in a large number of individual plants derived from each of the many segregating populations. Aflatoxin production was not assessed until homozygous lines (S5) were developed following selection for agronomic traits and resistance to foliar diseases during the earlier stages of inbreeding. From 2000 to 2002, self-pollinated ears were selected from each row to develop lines from each BC1 or F1 cross. At each stage of inbreeding, visual selection within and among lines was made on the basis of synchrony between pollen shed and silking, low ear placement, well-filled ears and resistance to lodging and foliar diseases, including Puccinia polysora, Bipolaris maydis and Curvularia lunata, under naturally occurring disease pressure at Ibadan, Nigeria. Sixty-five S5 lines were developed from the backcross populations and 144 S5 lines were derived from F1 crosses to be screened with the kernel screening assay (Brown et al., 1995).

Screening lines derived from populations with the kernel screening assay

The 57 S5 lines derived from the backcross populations were divided into seven groups, each containing three to eleven S5 lines, the recurrent parent and resistant and a susceptible inbred checks. These groups were screened for reduced aflatoxin accumulation (Brown et al., 1995). The maize inbred lines within each group exhibited a broad range in aflatoxin

Table 3. Mean aflatoxin values (ng/g) for a group of inbred lines derived from tropical * temperate crosses evaluated with the kernel screening assay.




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