INVESTIGATION OF THE HEREDITARY CHARACTER, WOOLLY, IN THE TOMATO.

52 Pages·2.162 MB·English

by  SHILLING, PAUL RICHARD

INVESTIGATION OF THE HEREDITARY CHARACTER,
WOOLLY, IN THE TOMATO
D issertation
Presented in P artial Fulfillment of the Requirements
for the Degree Doctor of Philosophy in the
Graduate School of The Ohio State
U niversity
By
Paul Richard Shilling, B.A.
The Ohio State University
1952
Approved hy:
Coadviser
Coadviser
Acknowledgements
The w r i t e r w is h e s to express much appreciation for
the helpful c r i t i c i s m s of the problem and manuscripts
given by t h e two m e n who served as co-advisors for this
problem, D r. Freeman S . Howlett and Dr. Elton F. Paddock,
the latter Ixaving o rig in a lly brought the problem to the
writer’s a t t e n t i o n , and also by the three other members
of the readd.ng co m m ittee, Dr. E. K. Alban, Professor
Donald Com in, and D r. G. A. Swanson. The w riter is also
grateful f o r the u s e of* the fa c ilitie s of the Department
of H o rticu ltu re a n d F orestry including the vegetable farm
where all f i e l d p i a n t i n g s were located and the vegetable
greenhouse w liere t i e species crosses were made and plants
for field p l a n t i n g s w ere raised; for seeds of a strain of
tomatoes c a rry in g th e woolly character made available by
Dr. Paddock who hstcl o rig in a lly obtained seeds from Dr. P. A.
Young of th e Texas A g ricu ltu ral Experiment Station; for the
buds used f o r the acetocarm ine smears which were from
plants g ro w in g in th e greenhouse of the Department of
Zoology and ^Entomology made available by Dr. Paddock; and
for a c u ttin g of l» y coper sic on hirsutum made available by
Dr. L. J. A le x a n d e r of the Department of Botany and Plant
Pathology a t the O liio A gricultural Experiment Station.
800485
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Table of Contents
Acknowledgements Page i
Introduction Page 1
Review of L iterature Page 5
Microtechnic Page 8
Experimental Procedure Page 10
Presentation of Results Page 13
Discussion of Results Page 41
Summary--------------------- ■ Page 46
Bibliography Page 47
Appendix Page 48
Autobiography Page 49
Investigation of the Hereditary Character, Woolly, in the
Tomato
Introduction
A condition of very profuse epidermal hair growth
exists in some strains of the cultivated tomato,
Lycopersicon esculentum M ill• The character originated in
a field of tomatoes grown By the Campbell Soup Company of
Camden, New Jersey (7). W. S. Porte (7) obtained a seed
sample of a tomato having this character from the New Jersey
A gricultural Experiment Station and called the character
"Angora". Later, Young and MacArthur (9), having obtained
the selection from Porte, published a description of the
character referring to i t both as "woolly leaves" and as
"woolly". Woolly plants are easily distinguished from
non-woolly plants. Due to the very profuse epidermal hair
growth, woolly plants appear grayish instead of a normal
green color. The woolly character has been used as a marker
gene in tomato breeding. For this reason, any information
which can be obtained concerning th is character should be
beneficial in further breeding work.
Five objectives are considered in th is problem:
1. Examination of embryo sacs containing zygotes and
embryos in an attempt to ascertain i f irreg u larities
in development resulted which could be attributed to
leth al action of the homozygous woolly character.
2. An attempt to determine i f there is a difference
between fru its of woolly and non-woolly plants in
number and germination of normal sized seeds.
3. Examination of pollen mother cell smears of anthers
from woolly plants to discern whether a deletion could
be demonstrated.
4. An accurate description of the woolly character.
5. An attempt to produce superwoolly tomato plants.
Upon selfing woolly plants, a ratio of 2/3 woolly to
1/3 non-woblly plants resulted (9). When a plant hetero­
zygous for a single pair of genes is selfed, either a
1/4 : 2/4 : 1/4 or a 3/4 : 1/4 phenotypic ratio would be
expected. Therefore, this observed 2/3 : 1/3 ratio in ­
dicated that the woolly character is leth al when homo-
zygously dominant, and any plant manifesting the woolly
character is heterozygous. Since the heterozygotes survive,
the woolly character is not a gametic lethal of both sperms
and eggs. I f the woolly character were a gametic lethal of
one kind of gamete only, a ratio of 1/2 woolly plants to
1/2 non-woolly plants would be expected upon selfing a
woolly plant, instead of the observed 2/3 : 1/3 ratio .
Therefore, the woolly character is not lethal to either
type of gamete. For this reason, i t must be assumed that
the leth al action of the homozygous woolly character takes
place sometime after fe rtiliz a tio n . I f th is lethal action
occurs during embryo development, then upon examination of
zygotes or embryos in fru its from self pollinated woolly
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plants, one might be able to observe disintegration of
approximately twenty five percent more zygotes or embryos
than in fru its from non-woolly plants. This would be
twenty five percent of a ll zygotes and embryos which
includes those which are normal and those which are disinte-
gratihg. . Hence, the embryo sac study.
I f the leth al action of the homozygous woolly character
affected embryo or endosperm development and as a con­
sequence also affected seed coat development, then in fru its
from self pollinated woolly- plants, one would expect
approximately twenty five percent fewer normal sized seeds
per fru it than in sim ilar fru its from non-woolly plants,
but nearly the same percent germination -should be found in
the normal sized seeds from both types of fru its.
Conversely, i f the leth al action did not appreciably affect
seed coat development as a consequence of its affect on
embryo or endosperm development, then one would expect
nearly the same number of normal sized seeds per fru it
in both woolly and non-woolly fru its, but approximately
twenty five percent less germination of the normal sized
seeds from fru its of woolly plants. Hence, the seed study.
Young and MacArthur (9) suggested that th is lethal
action could be due to a chromosomal deletion. Although
this is a possible explanation, there has been no cytological
evidence presented to support such an hypothesis. Hence,
the examination of pollen mother cell smears.
-4-
Young and MacArthur (9) stated that ’’the woolly
plants .......... had the usual pubescence of short 1-to-few-
celled hairs that were almost hidden by the abundant long
hairs of the woolly le a f le ts .” In this same publication (9),
an illu stra tio n is also included showing a ’’woolly tomato
plant with hirsute le aflets and stems due to the Wo a lle le .”
Evidently the woolly character can be expressed on both
leaves and stems. However, Young and MacArthur did not state
whether the woolly character can be expressed on a ll plant
parts, or whether expression is confined to leaves and stems.
Hence, the investigation concerning the description of the
woolly character.
In a ll strain s of another species of tomato,
Lycopersicon hirsutum Humb. and Bonpl., there is also a
condition of profuse epidermal hair growth, for which the
specific name hirsutum (which means hairy) has been applied.
Plants of th is species have epidermal hairs which are much
longer than those on plants of Lj_ esculentum, whether woolly
or non-woolly, as can be seen in Figures 22 and 23. I f
epidermal hair growth in these two species is conditioned
by different genes, upon crossing a woolly esculentum
plant with a hirsutum plant, offspring might resu lt
which had the combined epidermal hair growth of both
parents and would then be ’’superwoolly". Hence, the
investigation concerning production of superwoolly tomato
plants.
Review of Literature
Young and MacArthur (9) stated that a ra tio of 2/3
woolly to 1/3 non-woolly plants resulted when woolly plants
were selfed. However, in Paddock's (6) te sts, there was
usually less than 2/3 woolly plants, although in his
experience the variation was s ta tis tic a lly non-significant.
According to Soost (8), some segregating seed lots
have produced a few plants which he suspected were homo-
zygously woolly. Generally these plants did not develop
much beyond the cotyledonary stage. I f these few plants
were homozygously woolly, then th e .lethal action of this
character was not always fully manifested. The seed used
by, Soost came from W. S. Porte.
Soost (8^ also stated that in seeds germinated on
moist f ilte r paper, the number not germinating corresponded
to the number of expected homozygous woolly plants.
Dissection of the ungerminated seeds showed that a ll
contained well developed ehdosperm while the embryos were
at various stages of development but a ll poorly developed.
He therefore believed that the leth al action of the homo­
zygous woolly character affected the embryo and not the
endosperm and that the exact point of lethal action depended
on the genetic constitution of the individual embryo.
The chromosome to which the woolly locus is assigned
has been variously designated. Young and MacArthur (9)
designated i t as chromosome I . Lesley (5) designated i t as
chromosome A. Barton (3) designated i t as chromosome 2.
The primary basis for Barton’s classificatio n is chromosome
length at pachytene, chromosome 2 being the second longest
chromosome. Barton (2) also stated that chromosome 2 is the
nucleolar chromosome - that chromosome which is attached to
the nucleolus during most of f ir s t prophase in meiosis.
He (1) further stated that the nucleolus is attached to the
short arm of chromosome 2. I f th is information is correct,
only one pair of the twelve pairs of chromosomes need be
examined for evidence of a deletion and th is pair should be
easily identified due to its nucleolar association.
According to evidence presented by Lesley (5), those
genes already assigned to chromosome 2 are in the long arm.
According to the chromosome map presented by Young and
MacArthur (9), the woolly locus is th irty crossover units
from the m locus. Since the to tal crossover length of this
arm of the chromosome is seventy units, the woolly locus is
fairly near the midpoint of the long arm of chromosome 2.
The m locus is at zero crossover units or at one end of the
chromosome according to the map, which in re a lity is either
near the spindle fiber attachment point in the long arm or
at the d istal end of the long arm. Either way, th is would
place the woolly locus at least th irty crossover units from
the spindle fiber attachment point and even further from
the nucleolar attachment. Based on this information, the
approximate region of the chromosome on which a deletion
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might occur is known.
Soost (8) stated that the plants he suspected of being
homozygously woolly were densely covered with short bent
hairs. Young and MacArthur (9) would give the impression
that parts of woolly plants would be covered with long hairs.
Porte (7) considered woolliness applicable to the plant as
a while, i . e . , the character could be expressed on at
least most plant parts. Young and MacArthur’s description
of woolly would indicate that the character would not be
expressed on a ll or most plant parts. From this information
i t is evident that confusion exists relativ e to the woolly
character.
No lethal action has ever been reported to be
associated with the epidermal hair growth on hirsutum
plants. Therefore, one would hardly expect epidermal hair
growth of Lj_ hirsutum and esculentum to be governed by
identical genes, although i t might be governed by allelic
genes.