Rough sheath4 (Rs4) is an EMS-induced, dominant mutation which produces abnormally large vascular bundles in the leaf sheath (Neuffer, MNL 64:51, 1990). The gene was initially placed near the centromere of chromosome 7 with waxy reciprocal translocations (Neuffer, MNL 64:51, 1990). We report the results of four point linkage mapping to further define the position of Rough sheath4. A standard test cross was used to generate the mapping population as indicated in Table 1.  Approximately 480 kernels were separated into opaque and translucent classes and planted in our San Jose nursery. Seedlings were screened for the gl1 phenotype 4 weeks after planting. The virescent5 and Rough sheath4 phenotypes were scored at the time of tassel emergence. The data are consistent with the T-wx mapping data and place Rs4 approximately 10 map units from v5 and 3.6 map units proximal to gl1 on chromosome 7L very close to ra1. The map positions obtained for o2, v5 and gl1 are consistent with the current locations except that the o2 to v5 distance obtained in this experiment is 4 map units compared to 8 on the most current MNL map. The suggested map revision is:

 ---o2----------v5-------------------Rs4---gl1---
     20               24                            33        36
 

Table 1. Four point linkage data for o2 v5 Rs4 gl1.

F1: + + Rs4 +/o2 v5 + gl1
 

	Recombinants
	Par.	R1	R2	R3	R1+2	R2+3	R1+3	R1+2+3
	174	10	18	4	0	5	2	0
	203	5	17	3	1	2	0	0
Totals	377	15	35	7	1	7	2	0

% recombination          Region 1: 4.1± 1.0
                                     Region 2: 9.9± 1.4
                                     Region 3: 3.6± 0.9

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