Schmidt, Volker Stamenless-like mutants
with external ovules detected in
the ms series. (Submitted by R.
Hageman)
As reported, by Sawhney and Greyson,
the mutant sl-2 usually bears so-
called external ovules (E.O.) outside
the more or less reduced anthers.
Among the mutants of the ms series studied in detail in our laboratory, we found
three mutants (ms-15, ms-26, ms-33) which more or less resemble a typical
stamenless-mutant grown under Mid-European climatic conditions. The mutants behave
as single recessives. The original background has been replaced partly by
backcrossing with "Moneymaker". The three mutants are characterized by nearly
normal development of calyx and corolla, but the anthers are much changed in size
and shape. They are more or less degenerated, smaller than normal, and to some
extent twisted or distorted. In control plants the anthers are laterally slightly
joined to form a hollow cone, in the mutants they are grown together or coalesced
with the pistil and the ovary respectively. All three mutants possess the
remarkable feature of bearing naked external ovules outside (but rarely inside)
the stamens. The number of them increases from a few to more than one hundred,
depending on various conditions.
The number and extension of pollen sacs were influenced by the general
reduction of anther tissues, and there was no evidence of their existence in
extreme cases.
Although the three mutants are very similar, each has its own character,
so that they can be distinguished from one another macroscopically.
The external ovules are very like the normal ones inside the ovary.
Their development usually reaches the stage of macrospore differentiation.
No evidence has been obtained up to now whether or not a fertilizable
embryo sac is developed.
Steps of microsporogenesis identical to those described for the normal
wild type were observed in the stamens as a rule. Microspores were partially
produced, but most of them were found to be degenerated before anthesis.
Small amounts of viable pollen were formed, but as a rule not in
amounts such that hand pollination is successful.
This mutant was observed in a naturally
segregating population of variety Tip
top (IHR-7) (sp/sp,+u) during
evaluation of tomato germ
plasm collections at the Indian Institute of Horticultural Research,
Bangalore. The exsertion of stigma was between 1 mm to 3 mm above the tip of
the anther cone. The mutant was found to be breeding true for ex but
segregated into u+ and u fruit bearing plants. From these a homozygous
genotype IHR 7-1-5 (sp, u+, ex) was isolated. On crossing this line with
variety VF 36 (inserted stigma), the F1 and the parents were raised in three
replications and the position of stigma counted on ten flower clusters on each
of five randomly selected plants per replication. The percentage of ex in 7-1-
5 was 91.23 and of inserted stigma in VF 36 was 95.4. In the F1, 49.7 per cent
flowers were observed to have varying degrees of exserted stigma while in the
rest of the flowers the stigma remained at or near the tip of the anther cone.
From this data, the inheritance of exserted stigma appears to be conditioned
by varying degrees of dominance (Ognyanova, 1973) and may be governed by a few
genes (Rick & Dempsey, 1969) rather than a recessive gene (Dorosiev, 1970)
Tikoo, S. K., and A. B. Pal
A spontaneous mutant with
exserted stigma in tomato.
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