The narrow leaf and plant stature mutant narrow sheath (ns) was identified by Elsing and Albertsen as a single factor trait which sometimes displayed non-Mendelian patterns of inheritance (MNL 66:49-50, 1992). Subsequent analyses have determined that, in the original inbred line in which the mutant was isolated, the ns phenotype is inherited as a single recessive factor trait (Table 1). However, in the inbred lines Mo17 and B73, and in our laboratory Mutator-active inbred stock, the ns trait displays duplicate factor inheritance (Table 2). In order to locate the ns duplicate factor pair to chromosome arm using the B-A translocation series (Kindiger and Beckett, MNL 60:43, 1986), plants heterozygous for each of the dual factors were crossed as female onto hyperploid heterozygotes. Hypoploid plants were selected among the F1 progeny on the basis of 50% pollen semi-sterility, and plant phenotype (where applicable). The F1 hypoploids were either self-pollinated or backcrossed to ns mutants. The ratios of ns vs. non-mutant seedlings scored in the progeny of these crosses are presented in Table 3. The data indicate that the ns duplicate factors are located on chromosome arms 3S (ns1) and 4L (ns2). Molecular markers are now being used to RFLP map the ns loci to more precise locations.

Table 1. Number of progeny obtained from self of normal plants generated from ns x ns / + cross in original stock obtained from Pioneer Hi-Bred International.
 

Self #	Mutant No.	Normal No.	Total No.	Mutants (%)
1	24	62	86	27.9
2	14	40	54	25.9
3	7	29	36	19.4
4	48	150	198	24.2
5	8	25	33	24.2
6	12	21	33	36.4
7	22	78	100	22.2
Sum total	135	406	541	24.9

Fits a 3:1 ratio

Table 2. Combined sum total of number of progeny obtained from selfs of ns/Mo17 and ns/B73 plants.
 

F1 genotype	Mutant	Normal	Total	Mutants (%)
ns/Mo17	66	849	915	7.21
ns/B73	68	1153	1221	5.57
Combined sum total	134	2002	2136	6.27

X² = 0.001 Fits a 15:1 ratio

Table 3. Summary of ns1 and ns2 TB mapping results
 

TB parent	Hypoploid F1 plants (#)*	F1 cross	Total ns progeny (#)	Total progeny (#)	ns progeny (%)
1S	3	ns backcross	8	28	28.5
1L	2	ns backcross	26	111	23.4
3S	6	ns backcross	93	210	45.7
3L	8	ns backcross	97	410	23.7
4S	2	self	7	114	6.14
4S	2	ns backcross	13	81	16.3
4L	3	ns backcross	52	105	49.5
5S	9	ns backcross	93	409	22.7
5L	3	ns backcross	33	154	21.4
6S	2	ns backcross	13	70	18.5
6L	6	ns backcross	59	275	21.5
7S	3	ns backcross	35	157	22.3
7L	7	ns backcross	55	227	24.2
8L	3	ns backcross	38	174	21.8
9S	2	self	6	100	6.0
9S	5	ns backcross	29	146	19.9
9L	1	ns backcross	6	30	20.0
10S	3	ns backcross	35	160	21.9
10L	4	ns backcross	52	249	20.9

* only hypoploids which segregated ns mutant progeny included in table

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