The New Northrup King

Linkage of sugary enhancer (se) to 15.07 on chromosome 4L --Christine Bredenkamp, Diana Beckman, Michael Kiefer, Ann Majerus, Douglas Mead, Hope Sunderland, Carol Wangen and Edward Weck The sugary enhancer (se) gene (Ferguson, Rhodes, and Dickinson, J. Hered. 69:377-80, 1978) is a recessive modifier of the su1 locus, which is commonly used in sweet corn breeding. The se locus increases the sugar content of the kernel without the reduction of phytoglycogen commonly associated with the sh2, or "supersweet," varieties. LaBonte (Ph.D. thesis, University of Illinois, 1988) utilized the translocation stock TB-1LA-4L4692 and single kernel gas chromatographic sugar analyses to localize se to the long arm of chromosome 4, distal to zb6.

In order to map the sugary enhancer gene more precisely, we have analyzed a number of putative se inbreds with molecular markers (RFLPs) present on chromosome 4L. Figure 1 shows a schematic map of chromosome 4L along with hybridization patterns for 5 molecular markers. The hybridization banding patterns for each probe have been coded (pattern 1, none; pattern 2, black; pattern 3, horizontal lines). The codes for locus M15 are independent of the codes for the other loci shown (C2, 333, 15.07, M111). Locus 15.07 shows the same banding pattern in IL677a, the original source of se, and 7 of the 8 other inbreds analyzed (se 1a and se 1b are independent isolates of the same inbred). This suggests that locus 15.07 is linked to se. The other probes tested in the region, M15, C2, 333, and M111, are more polymorphic, having as many as 6 different patterns. This greater degree of polymorphism suggests that the chromosomal segment monitored by these probes was not transferred in construction of these se lines.

The similarity of these inbred lines for locus 15.07 on chromosome 4L suggests that sugary enhancer is located between loci 333 and 15.07. Loci 5.67 and 8.23 will be checked to determine if they also show the single hybridization pattern that suggests linkage. The differences observed between inbreds se 1a and se 1b and also with the other sugary enhancer inbreds, se 2-8, suggests that se 1a and b do not carry the sugary enhancer gene. In order to map the sugary enhancer gene more precisely, F2 or BC1 populations with IL677a as one parent will be constructed and analyzed for sugar content and chromosome 4L constitution.

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