Location of Rld1
--S. Chao and M. G. Neuffer

The dominant rolled leaf mutant (Rld1), for which two separate mutants were reported (MNL64:51), has been tested extensively for location using the full set of wx marked translocations. Both mutants Rld*-1441 and Rld*-1990 were tested against 23 translocations and the results were negative. From this we concluded that these mutants, which may be alleles, are located in some area of the genome not covered by the wx1 T set used. The most logical next step was to test the ends of the chromosome arms using the RFLP technique since these are the only areas not covered.

Bulking analysis was used to look for RFLP markers linked to Rld1. F2 populations segregating for the Rld*-1441 and Rld*-1990 alleles were used. Three genotypes, Rld1/Rld1, Rld1/+, and +/+, can be visibly distinguished in each F2 population. The genomic DNAs of plants having either the Rld1/Rld1 or +/+ genotype were bulked in equal amounts, with each bulk containing DNA from 8 to 9 individual plants. RFLP markers from distal ends of 20 chromosome arms were used to screen the bulks. Probe npi97 has a clearly detected polymorphism between Rld1/Rld1 bulk and +/+ bulk for both populations when the DNA is digested with HindIII. The polymorphism appears as a band present only in Rld1/Rld1 bulk and not in +/+ bulk. Probe npi97 was then used to hybridize F2 individuals to determine the map distance. Since probe npi97 detects duplicate loci on 9L and 1S (Burr, 1992), flanking markers on both were examined. The results showed that single locus probes bnl5.62 and umc157, which map distal to npi97 on 1S, have no linkage with the Rld1 locus; however, linkage between Rld1 and npi209 was detected. Probe npi209 also detects duplicate loci on 9L and 1S. However, no linkage was found by RFLPs detected by npi209, umc157 and bnl5.62. Therefore, we conclude that the Rld1 locus is located on 9L. The map distance is centromere - npi209 - 12cM - npi97 - 14cM - Rld1. This mapping is based on the results from a Rld*-1441 mapping population with 116 individuals. Even though the polymorphism detected by npi97 cannot be easily scored in the Rld*-1990 population, the location for Rld1 on 9L is confirmed. Two morphological traits, Bf1 and bm4, are known to be distal to npi97 on 9L (MNL 1992). The relative distances between Rld1, Bf1, and bm4 will be investigated.
A similar mutant, Ce1, reported by Chourey and Mouli in 1975 (Genetics 77:s11) has also been tested by Chourey with negative results. A test for allelism of Rld1 and Ce1 is in progress. 

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