engleski

Usefulness of F2, F2-SYN2, and BC1 populations derived from four adapted by exotic maize crosses

Choosing the right segregating generation (foundation population) in which to initiate selection is an important decision when adapted by exotic crosses are used to broaden the genetic base of a maize (Zea mays L.) breeding program. To account for differences in both mean and selection response, the usefulness (i.e. the predicted genotypic mean of a selected fraction) criterion was suggested for quantifying a foundation population's prospect for breeding. The objective of our study was to compare the usefulness of the F-2, F-2-Syn2 (= twice intermated F-2), and BC1 generations from four adapted by exotic initial crosses of inbred lines as foundation populations in hybrid breeding. A single seed was taken from each of the 50 earliest (a selected fraction of 4.4%) S-1 lines of the F-2, F-2-Syn2, and BC1 populations of the four initial crosses. S-1 plants were crossed with a common flint tester. The testcrosses were evaluated in four adjacent trials at two locations in southern Germany in 1996. In all instances, the BC1 testcrosses were the earliest entries for days to pollen shed, days to silking, and grain dry matter concentration (GDMC). Two adapted by exotic crosses had the highest grain yield in generation BC1, and the other two crosses in F-2. The smallest genetic variances for GDMC were obtained for the BC1 generation in all four initial crosses, while the variances of the F-2 and F-2-Syn2 populations were similar. Difference in components of genetic variance for grain yield among foundation populations were inconsistent across initial crosses. The predicted short-term selection response seems to be of minor importance for the usefulness ranks of foundation populations, emphasizing the importance of their means. The effects of intermating, backcrossing, and pre-selection for earliness turned out to be specific to the particular cross combination under study, indicating that there is no universally superior strategy for integrating exotic germplasm into adapted materials.

Adapted by exotic crosses. Inbred lines. Testcrosses. Usefulness. Variance

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