Cucurbit Genetics Cooperative Report 3:31 (article 17) 1980
Male Sterile-1: Stability of Expression
J. D. McCreight
U. S. Agricultural Research Station,
Salinas, CA 93915
Muskmelon male sterile-1 reported by Bohn and
Whitaker (1) has not been utilized in F1 hybrid melon production.
Plant breeders report ms-1/ms-1 plants difficult
to identify. Some breeders have stated that the male sterile
phenotype is not stable and have concluded that ms-1
is, therefore, of no value for melon hybrid production.
I report evidence indicating that expression of ms-1/ms-1
is stable, but that expression of male fertile siblings
Progeny 21322, and F1 from a cross of two plants heterozygous
for ms-1, was planted in the greenhouse in a 1:1
soil: sand mixture in a greenhouse flat; 48 seeds per flat.
Staminate flowers were scored at anthesis for male sterility.
Two to four flowers were scored per plant by two methods.
First, presence of pollen was determined by rubbing the
anther across the tip of a finger. Second, a crude squash
mount of an anther was stained with acetocarmine or methyl
blue and observed under low power magnification (100 X)
for presence of pollen. A flower was scored as fertile if
any pollen-like material was rubbed from the anthers. A
flower with even the slightest amount of pollen-like material
was scored as male fertile. All flowers from which none
or only a slight amount of pollen-like material was rubbed
from the anthers were examined microscopically for presence
of pollen. A plant was score as male sterile only if all
flowers were scored as male sterile by both methods.
Progeny 21322 segregated 74 Ms-1/_:27 ms-1/ms-1; a close
fit to the expected 3 fertile: 1 sterile ratio, x2 = 0.1616.
A few male sterile plants produced at least one flower with
distorted pollen grains similar to those reported by Bohn
and Whitaker (1) in ms-1/ms-1 plants. Male fertile
segregates produced three types of flowers with respect
to amount of pollen that was rubbed from the anthers: abundant;
sparse; and none. Three fertile plants produced flowers
that were observed to have no pollen when microscopically
examined. Thirteen percent of the flowers on male fertile
plants were scored as male sterile; 34% of the male fertile
plants had at least one sterile flower.
These results indicate that phenotypic expression of ms-1/ms-1
is stable. The source of confusion in selecting ms-1/ms-1
plants in a segregating population is variation in expression
of male fertile plants. Once a male fertile flower is found
on a plant, that plant should be scored male fertile and
rouged from the seed field. Before leaving a plant identified
as male sterile in the seed field, several (3 to 4) flowers
should be scored male sterile. It is essential to confirm
identification of male sterile plants by observing stained
anther smears under low power magnification. I have observed
as many as ten flowers on a plant to be male sterile when
check by rubbing the anthers. When examined under the microscope,
they were, however, fertile.
- Bohn, G. W. and T. W. Whitaker. 1949. A gene for male
sterility in muskmelon (Cucumis melo L.). Proc.
Amer. Soc. Hort. Sci. 53:309-314.