At the beginning of our search for QTLs we were curious to know if it would be possible to use a small population for QTL analysis. We identified a yield selected population "tail" for analysis which consisted of 17 S3 lines derived by single seed descent from the cross of E x F backcrossed once to E; E(2) x F S3. In addition, three other yield selected populations were selected for multiple population correlations with RFLP markers: G with 21 lines, H with 20 lines, and I with 34 lines.

Figure 1. Agronomic trait correlations with p<0.01; E(2) X F S3, 228 loci, 207 probes.

The 17 lines derived from the E(2) x F cross were hybridized with 207 probes. Correlations (p<0.01) with yield, percent harvest moisture, and days to 50% silk emergence are shown in Figure 1. Correlating markers are randomly distributed along 8 of the ten chromosomes of maize (there were no correlations on chromosomes 8 or 10).

In order to determine if these correlations were valid in more than one population, 38 probes showing significant correlations at the p<0.05 level in E(2) x F were hybridized to the three additional populations. Table 1 shows the four markers that correlated with agronomic traits in at least two populations (p<0.05). One marker correlated with yield in 3 populations (p<0.05). No markers correlated at a higher statistical stringency (p<0.01) in more than one population.

Table 1. Number and chromosomal location of probes correlating in multiple populations.

The dearth of multiple population correlations suggests that generalizing about yield promoting regions will be difficult. A more fundamental understanding of heterosis at the physiological level will be required to allow identification of important yield influencing chromosomal regions.

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