A new leaf mutant - narrow sheath (ns1)

--Evan Elsing and Marc C. Albertsen

A leaf-blade and plant-stature mutant (narrow sheath, ns1) was observed in one of our nurseries planted on Kauai, Hawaii, in November 1990. This mutant is characterized by a brachytic-like plant with abnormal leaf-sheath and leaf-blade development. The leaf sheath tapers from its base, through the ligule, and into the leaf blade. Between the ligule and the mid-length of the leaf, the leaf may only be as wide as the midrib. The leaf blade gradually widens near mid-length of the leaf. Although the leaf never attains the width of leaves on normal sibs, it does attain a normal-like appearance. The mutant phenotype also is demonstrated in the husk leaves. As the husk leaves are equivalent to leaf sheaths, they also display width reduction. Ears that formed were exposed on the two lateral sides of the ear. Mutant plants are 30-60% shorter than normal sibs, having very short internodes. Although they appear brachytic-like, there was no allelism to br2 (data not shown). We also made test crosses with lg1 and lg2, even though we visually verified that the ligule was present. Our results (data not shown) showed no allelism.

The mutant is true breeding and is mostly controlled by a single recessive gene. Supporting data are given in Tables 1-5. Remarkably, this mutant emerged independently from two Pioneer Hi-Bred corn breeding stations at Winterville (WT), North Carolina, and Tifton (TF), Georgia, utilizing Pioneer proprietary lines. One mutant came from an F4; the other from an F6. There were no immediate parents in common, however, one grandparent was in common for three of the four inbreds involved in the original crosses. The independent occurrences of this mutant were discovered serendipitously. A source of pollen was needed to attempt a pollination on one of the mutant plants (ns1-WT). Pollen was obtained from a row from Tifton. We had expected to find all normal progeny from this pollination. Instead we observed a 1:1 segregation of mutant and normal plants (data not shown). When remnant seed was requested from Tifton and planted in a subsequent nursery, ns1 plants segregated. Evidently the plant selected for pollination in November 1990 was heterozygous for ns1. We will therefore, refer to the Winterville mutant as ns1-WT and the Tifton mutant as ns1-TF. There is no reason, however, to believe that these mutant alleles are different from each other.

Table 1. True breeding results from ns1-WT self-pollination.
  # mutants # normal Total
Self #1 8 0 8
Self #2 9 0 9
  17 0 17

Table 2. Self of mutants from ns1-WT x ns1-TF crosses.
  # mutants # normal Total
Self #1 9 0 9
Self #2 5 0 5
  14 0 14

Table 3. Single recessive gene segregation from mutant plants of ns1-WT x +/ns1-TF crossed with normal sibs.
  # mutants # normal Total
Sib #1 9 9 18
Sib #2 10 10 20
  19 19 38

Table 4. ns1-WT sibbed w/ normal plants from a selfed heterozygote.
  # mutants # normal Total
Sib #1 0 20 20
Sib #2 8 9 17
Sib #3 9 10 19
Sib #4 4 15 19
Sib #5 0 20 20
Sib #6 2 9 11
-fits expected 1:2 segregation of a selfed heterozygote

-segregating progeny = 23 mutants:43 normals

x2 = 3.41

.10 > P > .05

... fits a 3:1 segregation ratio

Table 5. Selfed progeny segregation from ns1-WT crossed with Pioneer inbred J65.
  # mutants # normal Total
Self #1 4 15 19
Self #2 3 16 19
Self #3 1 17 18
Self #4 4 14 18
Self #5 3 15 18
Self #6 4 15 19
  19 92 111
x2 = 3.68

.10 > P > .05

... fits a 3:1 segregation ratio

As shown in Tables 1-5, ns1 segregates as a single recessive gene. We have some segregations, however, in which the mutant class is under-represented (e.g. Table 6). We will be growing larger numbers of progenies and testing across more genotypes to determine the true nature of ns1 expression.

Table 6. Selfed progeny segregations from ns1-WT crossed with Pioneer inbreds (G83 x W88-2).
  # mutants # normal Total
Self #1 1 19 20
Self #2 4 15 19
Self #3 2 17 19
Self #4 2 15 17
Self #5 3 17 20
Self #6 3 17 20
Self #7 2 18 20
  17 118 135
x2 = 11.08**

** significant at 1% level

... does not fit a 3:1 segregation ratio

We consulted several maize geneticists concerning the naming of this mutant. Suggestions included vestigial leaf, bladeless, narrow leaf, and narrow sheath. We finally decided that narrow sheath was the most descriptive, as it implies that the lower portion of the leaf also would be narrow. Our search of the literature did not find any previous descriptions of this type of mutant.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors

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