Segregation Data Suggest Male Sterility Genes gms and ms in Watermelon Are Not in the Same Linkage Group

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Cucurbit Genetics Cooperative Report 14:90-91 (article 32) 1991

B.A. Murdock, N. H. Ferguson and B.B. Rhodes
Departments of Horticulture (1st and 3rd authors) and Agronomy (2nd author), Clemson University, Clemson, SC 29364.

The gms and ms traits in watermelon have both been previously reported as the expression of single recessive nuclear genes in apparent non-allelic relationship (1, 2, 3). We now report data that suggest gms and ms exhibit independent assortment.

The cross [(MS MS gms gms) x (MS ms Gms Gms)] produced all pubescent, fertile F1 progeny (1). Twelve of these F1 plants were self-pollinated and 10-15 F2 progeny from each were evaluated for presence of gms and ms conditioned sterility. One of the F1 plants (termed P42) was determined to hve possessed a (Ms ms Gms gms) genotype. The remaining F2 progeny of P42 were then planted and staminate flowers evaluated both before and after fruit set. Germination was 98.5% (139/141).

P42 produced 139 F2 plants which segregated for pubescence and glabrousness in a 3:1 ratio (105 pubescent : 34 glabrous) P = 0.90. However, four phenotypic classes could be recognized within this F2 population.

  1. Pubescent fertile. All pubescent fertile plants had normal anthers. It should be noted that fertile anthers produced on (Gms gms) and (Ms ms) are normal and indistinguishable from one another.
  2. Pubescent sterile. The only staminate sterility manifested in the pubescent plants was that usualy found in (ms ms) plants. In such genotypes only very small, undeveloped anthers are present. The gms conditioned sterility found only in glabrous plants (hence the “g” of the gms) has much larger, more developed non-functional anthers andis easily distinguishable from the ms condition if comparative evaluation is made throughout the growing season.
  3. Glabrous sterile with “gms” type anthers and
  4. Glabrous sterile with “ms” type anthers.

The analytical crux of this report is based upon the observation that the sterility produced by gms and ms are distinguishable even when the ms conditioned sterility is found within glabrous plants. The gms conditioned sterility produces anthers which, although they do not dehisce, are much larger than the ms conditioned type. The sterile anthers of this gms conditioned sterility can sometimes approximate the size of fertile anthers, especially late in the season. The ms conditioned sterility produces only small, shrunken anthers throughout the season. In large unopened flowers, ms conditioned male-sterility produces a very “hollow” flower bud when simply pressed between the fingrs. This can be compared to the gms conditioned male-sterility, with its sometimes much larger yet nonfunctional anthers, which can manifest very “full” unopened flower buds during its life cycle when sensed by a similar finger-tip evaluation. Our preliminary cytological analysis of the gms and ms conditioned sterilities seem to confirm the distinctions made from these simple visual observations and touch.

By distinguishing 4 phenotype classes within the F2 generation of P42, a Chi-Square analysis based on independent assortment of gms and ms was possible. These data are listed in Table 1.

Table 1. Segregation ratios of the F2 of P42 into 4 phenotypic classes and Chi-Square analysis assuming independent assortment of gms and ms.

Phenotypic Class

Putative genotype

Number of plants

Expected if 9:3:3:1 segregatrion
Pubescent fertile (Ma_Gms_) 85 78.18
Pubescent sterile with “ms” type anthers (ms ms Gms gms) 20 26.06
Glabrous sterile with “gms” type anthers (Ms_gms gms) 25 26.06
Glabrous sterile with “ms” type anthers (ms ms gms gms) 9 8.68
Chi-Square – 2.05; 3 d.f.

P = 0.50-0.70

Assumptions necessary to interpret our observations in this manner are (1) the glabrousness of homozygous gms overrides any expression of pubescence, and (b) the male sterility of homozygous ms overrides the expression of homozygous gms. Further evaluation of the glabrous material in this F2 population has been thwarted by extreme female sterility.

Literature Cited

  1. Murdock, B.A., N.H. Ferguson and B.B. Rhodes. 1990. Male-sterile (ms) from China apparently non-allelic to glabrous male sterile (gms) watermelon. Cucurbit Genet. Coop. Rept. 13:46.
  2. Watts, V.M. 1962. A marked male-sterile mutant in watermelon. Proc. Amer. Soc. Hort. Sci. 81:498-505.
  3. Zhang, Xing-ping and Ming Wang. 1990. A genetic male-sterile (ms) watermelon from China. Cucurbit Genet. Coop. Rept. 13:45-46.