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MEDEDELINGEN LANDBOUWHOGESCHOOL
W A G E N I N G E N • N E D E R L A N D • 70-20(1970)
SOMATIC CHROMOSOME NUMBERS
IN 'ELATIOR'-BEGONIAS
J. C. A R E N D S
Laboratorium voor Tuinbouwplantenteelt,
Landbouwhogeschool, Wageningen, The Netherlands
PRO-DLO
BIBLIOTHEEK
JPfàtfcus16
67QÖAA Wageningen
(Received 8-V-1970)
INTRODUCTION
One of the two groups of winter flowering begonia hybrids, which are cultivated in temperate zones as potted plants, has been developed by crossing
various tuberous begonia species hybrids with the winter flowering species
B. socotrana. The other group of hybrids, the so-called 'Gloire de Lorraine'begonias, comprises varieties bred as interspecific hybrids of B. dregei and
B. socotrana. Thispaper deals exclusively with varieties of the first group, which
are known in continental Western Europe as 'Elatior'-begonias. The denotation
'Elatior' was derived from the varietal name of a hybrid introduced by VEITCH
in 1906. In British literature the varieties are usually refered to as 'Winter
flowering begonia hybrids' only. From the context of the articles it becomes
clear which of the two groups is being discussed. 'Elatior'-begonias are also
called 'Hiemalis'-begonias from the name Begonia x hiemalisproposed for this
group by FOTSCH (1933).
The 'Elatior'-begonias are readily distinguishable from the 'Gloire de
Lorraine'-begonias by larger asymmetrical leaves and larger flowers in various
colours which range from white through pink and apricot to crimson and
scarlet. Moreover, the flowers can be, depending on variety, single, semidouble or double. The 'Gloire de Lorraine'-begonias, on the other hand, have
roundish peltate leaves and flowers that are always single, white or light to
deep pink.
Although some cases of further breeding with 'Elator'-begonias have been
reported, which could indicate some degree offertility, for allpractical purposes
the varieties are sterile and hence propagated asexually by leaf or stem cuttings.
Because of renewed interest in winter flowering begonias the breeding of
additional and superior varieties has become desirable. Compact growth,
floriferousness, year around flowering and resistence to powdery mildew are
among the most important goals of breeding. Also the production of plants
Meded. Landbouwhogeschool Wageningen 70-20 (1970)
1
from seed instead of cuttings might be attractive, as this would mitigate the
spreading of systemic pests known in Begonia such as nematods and viruses.
As knowledge of the chromosome numbers of species and hybrids has proved
to be a valuable aid in breeding, a cytological investigation was undertaken of
the twenty-three 'Elatior'-begonias which could still be found in 1968 and 1969.
The results are presented in this paper.
SURVEY OF LITERATURE
History
A survey of horticultural journals mentioned in Table 1shows that about one
hundred 'Elatior'-begonias have been produced since the introduction of the
first variety 'John Heal' in 1885. Since that year three more or less overlapping
phases are distinguishable in the development of new varieties. During the
first phase, from 1885 until 1935 two British establishments, namely J. VEITCH
& SONS and W. CLIBRAN & SONS have been active in breeding. Relatively
detailed information concerning the activities of the former firm is available
through publications of two of its owners, H. J. VEITCH (1893) and J. H. VEITCH
(1906) and two hybridizers, HEAL (1916) and GLEED (1961), both employed by
VEITCH. Very little information however, can be found about CLIBRAN & SONS
(EVISON & POULTON, 1961 and COUTTS, 1925), who introduced their first hybrid
in 1907. From that year onwards VEITCH and CLIBRAN both regularly introduced
new variétés until 1914, when the former retired. According to GLEED the begonia material of VEITCH was purchased by L o w of Enfield, but in the literature
no further mention is made of that firm in respect of 'Elatior'-begonias. In
Britain nobody else than CLIBRAN seems to have done any hybridizing since
1914and it is therefore very likely that CLIBRAN has been the solebreeder of 'Elatior'-begonias from 1914 until the late 1930's.
In 1910 Begonia 'Elatior' was introduced as the first hybrid o f t h a t type into
the Netherlands. It took another twenty years however, before Dutch growers
began to introduce new varieties, which mostly originated as mutated forms
of English bred varieties. During the second phase (1930-1960) J. BAARDSE D Z N
can be considered as the most productive one among the Dutch growers, by
then all located at Aalsmeer, the Netherlands.
The third phase started in 1955 when the German breeder O. RIEGER at
Nürtingen introduced the 'Elatior'-begonia 'Riegers Leuchtfeuer', which was
followed by several other varieties during the next decade. These varieties
resulted from a breeding program initiated in 1928. They surpass the older
varieties in qualities such as mildew resistance and floriferousness ( H A H N ,
1958).
The origin of the
'Elatior'-begonias
By definition the 'Elatior'-begonias are the result of crossing various tuberous
Begonia species hybrids and B. socotrana, in which the species was used as the
male parent since the reciprocal combination was incompatible (GLEED, 1961).
2
Meded. Landbouwhogeschool Wageningen 70-20 (1970)
The pluriformity whichisfound inthe 'Elatior'-groupisaconsequenceofthevariation ofthetuberhybridsused.Theselectionofbudsportsontheotherhand has
mainly yielded varieties that are rather similar to the original clone. Changes in
flower colours have been most frequently reported, while mutation probably
also led to more compact growth (WASSCHER, 1949 and HAHN, 1968).
Although the majority of the 'Elatior'-begonias originated in the way mentioned above, some varieties were, according to the literature, introduced along
the following lines.
1. B. socotrana X tuberhybrid
This line of breeding in which B. socotrana was used as the seed bearer was
only succesful intwocrossesyielding theearly varieties 'John Heal' and 'Winter
Gem', respectively (HEAL, 1916).
2. 'Elatior'-begonia X tuberhybrid
This line of breeding resulted in the introduction of what may be called
'second generation 'Elatior'-begonias'. These are firstly 'Adonis', the result
of a cross of the 'Elatior'-begonia 'John Heal' with an orange tuberous
hybrid (VEITCH, 1906)and secondly 'Eveleens' Orange', a cross of the 'Elatior'begonia 'Flambeau' and the tuberhybrid 'Flamboyant' (Anonymous, 1961).
3. 'Elatior'-begonia X B. socotrana
According to HAHN (1958) two recently introduced varieties 'Frau Gertrud
Rieger' and 'Gartenmeister Rieger' are both the result of backcrossing the
'Elatior'-begonia 'Riegers Leuchtfeuer' with B. socotrana. Earlier HOFFMANN
(1955) reported similarly when he mentioned that about 10% of the seedlings
which RIEGER obtained by crossing a tuberhybrid with B. socotrana were
fertile and could be backcrossed with the species.
In general the tuberhybrids used in the hybridizations are described by the
colours and the type of the flowers only, but in the following cases the tuberhybrids are specified.
1. Begonia 'Viscountess Doneraile' = [(boliviensis x unknown species)
X veitchii] was crossed with B. socotrana and yielded 'John Heal' (VEITCH,
1906).
2. The tuberhybrid 'Moonlight' (supposed to be B. pearcei X B. dregei)
crossed with B. socotrana yielded 'Agatha' (VEITCH, 1906).
3. One reference (Anonymous, 1912a) cites the 'Elatior'-begonia 'Optima' as
a hybrid of a 'pearcei-seedling' and B. socotrana. A second reference (1912b)
gives the same parentage for 'Emita', a variety introduced simultaneously with
'Optima'. According to GLEED (1961), when reporting in retrospect about his
breedingwork with VEITCH, thelattertwovarietieswereamonganumberofseedlings bred by crossing B. socotrana with a few dozen unnamed tuberhybrids.
It appears that the references relating to theparental tuberous Begonia hybrids
are rather unreliable.
Theparental species
Soon after B. socotrana was collected by I. B. BALFOUR in 1880on the island
of Socotra, situated south ofArabia inthe Indian Ocean, the specieswas named
Meded. Landbouwhogeschool Wageningen 70-20 (1970)
3
in 1881 byJ. D. HOOKER. Thehybridizer J. HEAL performed the first crosses
with tuberous hybrids in 1883,after which the first 'Elatior'-begonia 'John
Heal' was exhibited in 1885 (VEITCH, 1906).
Less certainty exists about the origin of thetuberhybrids. Asfar as known
four Peruvian and two Bolivian species form the genetic background of the
tuberhybrids, which in turn contributed genetically to the 'Elatior'-begonias.
The Bolivian species,B.boliviensisand B.pearcei wereintroduced into England
in 1865and 1866respectively. The Peruvian species were B. clarkei (1863),
B. veitchii(1866),B.rosaefloraand B.davisii(both 1876).Thefirsthybrid which
was used intensively in further breeding, was raised by J. SEDEN as a cross
between B.boliviensisandan unknown Bolivian species (VEITCH, 1906).Ithas
been suggested that this unkown species isidentical with B. cinnabarina,which
wasimported in 1847.Thishowever isunlikely sinceatthetimeofearly hybridizations that species hadalready disappeared from thecollections.
Cytological investigations
Recently DOORENBOS & LEGRO (1968) corroborated the observation by
MATSUURA & OKUNO (1936) of 2n = 28 chromosomes in B. socotrana. The
sameauthors (LEGRO &DOORENBOS, 1969)alsodetermined thesomatic chromosome numbers of some of the progenitors of the tuberous hybrids. Their
observations indicated 2n = 28forB.boliviensis,B. davisii andB. veitchiiand
2n = 26for B.pearcei. From aninvestigation of some hybrids WAINES (1968)
suggested that B. clarkei and B. rosaeflora have either 2n = 26 or 2n = 28
chromosomes. MEYER (1965) investigated some species and hybrids butbecause of aneusomaty she did not present definite numbers. WAINES further
concluded that the 'Elatior'-begonias he investigated were alltriploids having
42 chromosomes, as a result of hybridizing tetraploid tuberhybrids with the
diploid B. socotrana. LEGRO & HAEGEMAN (1969, unpublished) found forthe
large flowered Belgian tuberhybrids tetraploid numbers of 52, 54and56chromosomes, whereas thesmaller flowered tuberhybrids were either tetraploids,
triploids or diploids. According to OKUNO & NAKAI (1954) the chromosome
numbers ofthe tuberhybrids form an aneuploid series.
MATERIALS ANDMETHODS
Materials
Table 1lists the'Elatior'-begonias studied which form a part ofthe Begonia
collection of the Department of Horticulture, Agricultural University, Wageningen. Some of the materials were kindly provided byMessrs. P. Eveleens &
Sons, Man Brothers, both atAalsmeer, the Netherlands andMessrs. O. Rieger,
Nürtingen, Germany.
In Table 1, the varieties, except the ones arisen as sports, have been
arranged chronologically according to the dates ofintroduction. The sports
follow immediately after the original clones. For reasons of simplicity the
literature references specific to the varieties have been placed in a separate
column. Varieties arebriefly described byflowercharacteristics, such ascolour
4
Meded. Landbouwhogeschool Wageningen 70-20 (1970)
- as checked by the Horticultural Colour Chart -, average size - measured as
the largest diameter -, type and sex, while in a few cases peculiarities are mentioned. It should be pointed out here that flower types are normally described
as single, semi-double or double, depending on the number of stamens that
have become tepaloid. Some varieties with flowers classified as single have
varying numbers (1-5) of small additional tepals. In semi-double flowers the
additional tepals are smaller than the normal perianth and diminishing in size
towards the centre, but in double flowers these tepals are sized alike to the
perianth. It was observed that under normal greenhouse conditions transition
between semi-double and double forms may occur. Although most varieties
have male flowers only, a few single flowered clones are regularly bisexual.
In semi-double or double flowered varieties no rudiments of reproductive organs were noticed.
Methods
Roottipsof 1 cmlength were pretreated during 5hours in a 0.002 N aqueous
solution of 8-oxyquinoline at 20°C, fixed and hydrolized in 1 N HCl for 12
minutes at 60°C, stained in leucobasic fuchsin after Feulgen during 4 hours,
rinsed in several changes of water and kept in water overnight. After squashing
the meristematic parts (0.5 mm) in 45%acetic acid the slides were made semipermanent by sealing with parafin. Cells were studied with a Carl Zeiss microscope, using a 100 X apochromatic objective (N.A. = 1.32) and achromatic
condensor (N.A. = 1.4), both with phase contrast setting, 12.5 X wide angle
oculars and photographed on Gevachrome 32 plates.
Efforts to improve the differential staining of the nuclear material and other
cell contents by alterations in time and temperature or the use of additional
fixatives were unsuccesful. Treatment of the tissues in various mixtures of
ethyl alcohol, acetic acid and chlorophorm caused considerable dehydration,
whereas staining decreased. Staining fluids based on e.g. orcein, carmine,
haematoxilin, usedeither incombination with orwithoutfixativesincorporating
substances such as formalin and various alums yielded extremely poor results.
The schedule mentioned above gave the best results, but phase contrast equipment was indispensable.
RESULTS
The present observations indicate that the somatic chromosomes of the
'Elatior'-begonias fall into two groups according to size. The first group
comprises long chromosomes with a length of about 1.5-3.0 \i whereas the
chromosomes of the second group have a length of about 0.5-1.0 \i. By comparison with the chromosomes observed by DOORENBOS & LEGRO (1968) and
LEGRO & DOORENBOS(1969)in those species putatively involved in the breeding
of the 'Elatior'-begonias, it is evident that the longer chromosomes have been
inherited from the tuberous Begonia species and the shorter ones from B.
socotrana.
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PLATE I. Begonia 'Elatior', a variety introduced by VEITCH in 1906. The varietal name 'Elatior' is used in Western Europe to indicate a group of similar hybrids, which was developed
by crossing tuberous Begonia hybrids with the species 3. socotrana. The group is also known
under the name Begonia x hiemalis Fotsch.
8
Meded. Landbouwhogeschool Wageningen 70-20 (1970)
FIG. 1. 'Elatior'-begonia 'Man's Favourite', 2n = 41. Root tip aquash. Somatic metaphase
showing 27 long and 14short chromosomes. The long arrow indicates a long chromosome
carrying a satellite,the short arrow a chromosome-like body, x 4500.
Meded.Landbouwhogeschool Wageningen 70-20 (1970)
9
It appears from Table 2 that all except three varieties have a consistent
number of 14 short chromosomes within their complements. In addition to
these short chromosomes the varieties have, depending on the variety, various
numbers of either 26, 27, 28, 52 or 56 long chromosomes. It was found that
from the twenty-three varieties studied three have 26 chromosomes, whereas
the next fifteen varieties have 27 long ones. From the remaining five varieties
three have 28 long and the last two varieties have 52and 56long chromosomes
respectively.
Concerning the morphology of the chromosomes a few peculiarities have
been noted. The chromosomes were most distinctive when heavily condensed,
the long ones attaining oval to rod-like shapes, the short ones becoming
similarly shaped but usually less regular in their outlines. After staining according to the method described and using phase-contrast setting the long chromosomes had a brilliant orange-red appearance, by which they contrasted with the
often more faintly stained short chromosomes. In many cells however, a few or
several short chromosomes were less condensed and less distinguishable against
the often dense cytoplasmn. Cells suitable for photographic representation were
scanty. In general centromeres were not distinct, but occasionally they could
beseen(figure 4,arrow). Sometimes, achromosome carrying asatellite(figure 1,
long arrow) and some small chromosome-like bodies (figure 1, short arrow)
were observed. Similar observations were made by LEGRO & DOORENBOS
(1969).
TABLE 2. Number of somatic chromosomes in 'Elatior'-begonias
Variety
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
10
Riegers Leuchtfeuer
Optima
Johan C. Mensing
Elatior
Baardse's Wonder
Kees Tas
Exquisite
Man's Favourite
Altrincham Pink
Emita
Rosalind
De Ridder's Yellow
Frau Gertrud Rieger
Lâchsorange
Goldlachs
Koningin Juliana
Aphrodite
Schwabenland
Rose Queen
President
Nelly Visser
Flambeau
Eveleens' Orange
Number of chromosomes
Long
Short
Total
26
26
26
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
28
28
28
52
56
about 9
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
about 12
14
14
14
7
35
40
40
41
41
41
41
41
41
41
41
41
41
41
41
41
41
41
40
42
42
66
63
Number of cells
analyzed
15
21
22
3
4
8
5
11
12
4
4
4
31
6
7
4
18
12
24
6
12
6
14
Figure
2
1
3
4
5
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FIG. 2. 'Elatior'-begonia 'Optima'. 2n = 40. Root tip squash. Somatic metaphase showing
26long and 14short chromosomes, x 2500.
FIG. 3. 'Elatior'-begonia 'Koningin Juliana', 2n = 41.Root tip squash. Somatic metaphase
showing 27 long and 14short chromosomes, x 2500.
Meded. Landbouwhogeschool Wageningen 70-20 (1970)
11
•'V ;
ta
FIG. 4. 'Elatior'-begonia 'Nelly Visser', 2n = 42.Root tip squash. Somatic metaphase showing28 longand 14short chromosomes.Thearrow indicates achromosome with a distinctive
centromere, x 2500.
«WH » f - 1 1 - ' « ^ * ^ - ^ * * . , . * - * . ! * ^ ^ ^ ^ ^
i .•>.-
...^'Ê1"?.. A
FIG. 5. 'Elatior'-begonia 'Flambeau', 2n = 66. Root tipsquash.Somaticmetaphase showing
52long and 14short chromosomes, x 2500.
12
Meded. Landbouwhogeschool Wageningen 70-20 (1970)
DISCUSSION
Chromosome numbers
Out of twenty-three investigated 'Elatior'-begonias a majority of fifteen
varieties have a complement of 27 long and 14short chromosomes. The observations do not provide any indication by which these fifteen could be characterized cytologically. Even the chromosome complements of varieties, such
as 'Elatior' and 'Schwabenland' (Table 1, no 1and 23), which were bred and
introduced at an interval of six decades do not differ perceptibly.
From the three varieties having 26 long chromosomes within their complement, one, 'Riegers Leuchtfeuer', differs from the other two, 'Optima' and
'Johan C. Mensing', in having a few less than the expected 14short chromosomes.
A similar reduction in number of the short chromosomes is found in the
first of three varieties, 'Rose Queen', 'President' and 'Nelly Visser', which have
28 long chromosomes within their complements.
Somatic chromosome numbers of some of the supposedly ancestral species
of the 'Elatior'-begonias have been recorded by LEGRO & DOORENBOS (1969).
They found n = 13 for B. pearcei and n = 14 for B. boliviensis, B. davisii,
B. veitchii and B. socotrana. Comparison of these numbers with the somatic
chromosome numbers found in the varieties discussed sofar, leads to the conclusion that these chromosome numbers (40, 41 and 42) reach atriploid level.
WAINES (1968) from an investigation of some 'Elatior'-begonias concluded
similarly, buthedid not observechromosome numbers other than 42. It can be
concluded that 'Flambeau' (Table 2, no 22, 2n = 66) is a pentaploid variety,
having a tetraploid number (52) of long chromosomes and a haploid number
(14) of short B. socotrana chromosomes.
A comment on the observation of 56 long and 7 short chromosomes in the
last variety, 'Eveleens Orange', listed in Table 2 will be given on page 14.
Parentage
The diploid numbers of long chromosomes as observed in twenty-one
'Elatior'-begonias may well have been inherited from tetraploid Begonia
tuberhybrids, since LEGRO & HAEGEMAN (1968, pers. comm.) found for some
large flowered Belgian varieties tetraploid numbers of 52, 54 and 56. The observation of 26, 27 and 28 long chromosomes in these twenty-one 'Elatior'begonias implicates a rather regular gamete formation on the side of the female
tuberous parent plants. The possibility that some diploid tuberous hybrids
produced diploid egg cells, which after fusion with the haploid male B. socotranagametes yielded triploid 'Elatior'-begonias cannot be excluded. However,
the regular formation of diploid gametes by diploid plants seems rather exceptional. Moreover, preliminary observations indicated that crosses between
diploid tuberous Begonia hybrids and B. socotrana do not succeed. Therefore,
it is likely that the tuberous hybrids used in the hybridization were indeed
tetraploids.
The pentaploid variety 'Flambeau' probably resulted from fusion of a tetraMeded. Landbouwhogeschool Wageningen 70-20 (1970)
13
ploid gamete of a tetraploid tuberhybrid with a haploid gamete of B. socotrana.
It may have also originated from the hybridization of an octoploid tuberhybrid
with B. socotrana but this is less likely since no octoploid tyberhybrid has been
reported sofar. The highest chromosome number found in tuberhybrids is 72
(OKUNO & NAKAI, 1954). LEGRO (pers. comm.) never encountered ploidy
levels higher than four in his studies of Belgian and English tuberhybrids.
The variety 'Eveleens' Orange' (Table 2, no 23) is recorded in the literature
(Anonymous, 1961) as a second generation 'Elatior'-begonia, which originated
as the result of hybridizing the 'Elatior'-begonia 'Flambeau' with the tuberous
hybrid 'Flamboyant'. 'Flambeau' has 52long and 14short chromosomes (Table
2, no 22) and considering this high number of chromosomes the formation
of some viable gametes might be possible. 'Flamboyant' is a triploid tuberous
hybrid (MEYER, 1965; LEGRO, pers. comm.) having 42 somatic chromosomes,
which produces some seed and hence some functional gametes. Consequently
hybridization of 'Flambeau' and 'Flamboyant' might be partially succesfull
and it appears that 'Eveleens' Orange' is the result of such a hybridization.
Another 'Elatior'-begonia, 'Frau Gertrud Rieger', is reported as the result
of backcrossing the 'Elatior'-begonia 'Riegers Leuchtfeuer' with B. socotrana
(HAHN, 1958).'Frau Gertrud Rieger' has the most common chromosome number of 27 long and 14 short chromosomes (Table 2, no 13). This observation
disqualifies the vague report by HAHN, since it is hard to explain how 'Riegers
Leuchtfeuer', which has 26 long and about 9 short chromosomes (Table 2,
no 1),could yield a hybrid having 27 long and 14 short chromosomes.
According to HAHN (1965) a strain of tuberhybrids named B. X Bertinii
'Leuchtfeuer Compacta' was introduced by ROTHMUND in 1952. The use of
the name 'Leuchtfeuer' suggests that RIEGER mighthavecrossed a tuberhybrid
named 'Leuchtfeuer' with B. socotrana, after which the resulting 'Elatior'begonia received the name (Riegers) 'Leuchtfeuer' too. Possibly RIEGER further
mentioned that he repeated the cross of the tuberhybrid 'Leuchtfeuer' with
B. socotrana which was misinterpreted by HAHN (1968) as a backcross of the
'Elatior'-begonia 'Leuchtfeuer' with B. socotrana. Because Mr. RIEGER passed
away several years ago it is uncertain whether the situation pertaining to these
varieties will be ever clarified.
A reference of literature (Anonymous, 1912a) specifies 'Optima' as a hybrid
of a '£.pearcei-seedlmg and B. socotrana'. The parentage of the simultaneously
introduced variety 'Emita' is specified as a 'single orange tuberhybrid and B.
socotrana'. Contrary to this reference another one of the same year (Anonymous, 1912b)specifies the '5. /?ea/*ce;'-seedling'mentioned before asthe tuberous
parent plant of 'Emita' and the single orange tuberhybrid as one of the parent
plants of 'Optima'. The observation of 26long chromosomes and 14short ones
in 'Optima' and its sport 'Johan C. Mensing' (Table 2,no 2and 3) corroborates
that B.pearcei was involved, as LEGRO & DOORENBOS (1969) found a chromosome number of 26 for this species. Nevertheless, the occurrence of the diploid
number (26) of long chromosomes in 'Optima' can only be explained by assuming that the B. pearcei-seedMng in question was either a tetraploid or a tetra14
Meded. Landbouwhogeschool Wageningen 70-20 (1970)
ploid hybrid having B. pearcei as one of its ancestors. The same tetraploid
hybrid may have well produced gametes with 27 chromosomes, which after
fusion with a B. socotrana gamete gave rise to 'Emita'.
The variation in the number of long chromosomes recorded points to the
significance of the tuberous hybrids used in the hybridization. The question
relating to the problem as to what species other than B. socotrana contributed
genetically to the 'Elatior'-begonias, can be answered when the parent species
of the tuberous hybrids are known. Earlier it was concluded that the tuberhybrids used in the hybridization were tetraploids having chromosome numbers
of 2n = 52, 54and 56. VEITCH (1906) lists seven species, one of which was lost
before it could be described, as the parents from which the early tuberous
hybrids were raised.
Cytological investigation by LEGRO & DOORENBOS (1969) of four of these
species indicated a chromosome number of 2n = 26for B.pearcei and 2n = 28
for B. boliviensis, B. davisii and B. veitchii.
AsB. clarkeiis closely related to B. cinnabarina,which has 26 somatic chromosomes (LEGRO & DOORENBOS, 1969), while B. rosaeflora is but a form of
B. veitchii, it does not seem too far-fetched to suppose chromosome numbers
of 2n = 26 for B. clarkei and 2n = 28 for B. rosaeflora. The evidence, incomplete as it is, suggests that the tuberous hybrids originated by interbreeding of
species with n = 13 and n = 14 chromosomes. It seems reasonable to assume
that once tetraploidy was established, tetraploid tuberhybrids have been interbred continuously, which has lead to the development of an aneuploid series
of tetraploid tuberhybrids.
Although MEYER (1965) established karyotypes of some species and tuberhybrids, no morphological features of the long chromosomes appeared to be
useful to characterize the various ones. Thus chromosome numbers as well as
chromosome morphology do not provide conclusive evidence as to which
species were involved and to what extent they contributed genetically.
Phenotype and chromosome number
Varieties developed by selection of sports of cultivated varieties exhibited
neither deviating chromosome numbers nor visible chromosome mutations.
This means that the observed phenotypic alterations did not result from the
loss or acquisition of chromosomes, but are probably due to gene mutations.
Although it remains possible that structural mutations occur, it seems unlikely
that, considering thenature and the sizeofthechromosomes, structural changes
such as delations or inversions can be demonstrated microscopically.
There appears to be some correlation between flower type and chromosome
number in thetriploid 'Elatior'-begonias, asthere is a tendency for the numbers
of tepals to increase with the number of long chromosomes. Varieties with 26
long chromosomes in their complement are single flowered, those with 27
long chromosomes are, depending on variety, single, semi-double or double,
while varieties with 28long chromosomes are, also depending on variety, either
semi-double or double.
Meded. Landbouwhogeschool Wageningen 70-20 (1970)
15
Apart from this the pentaploid variety 'Flambeau' which has 52 long chromosomes within its complement, is also single flowered. If the 52 chromosomes
are formed by four genomes each consisting of 13 chromosomes, it may be
possible that thegenomes ofB.pearcei(and perhaps B.clarkei) carrymore genes
for single flowers than the genomes with 14 chromosomes.
Variation in chromosome number
In the present study relatively low numbers of cells suitable for analysis
werefound:itisestimated that overa thousand of root tipshave been squashed
in order to obtain the number of about 250 analyzable cells. Difficulties were
met with when determining the exact number of short chromosomes, which
occasionally fell short of theexpected haploid number (n = 14)ofB. socotrana.
Under 'Results' it was mentioned that these short chromosomes often appeared
as narrow thread-like structures, which could hardly be distinguished. This
feature was particularly striking when the long chromosomes were observed
in a phase not yet fully condensed. However, even when the long chromosomes
appeared fully condensed a few short chromosomes were occasionally less
visible. This phenomenon can be explained by assuming that the long chromosomes on one hand and the shorter ones on the other do not contract synchronously. It ispossible that thispostulated asynchrony delays the contraction
of the short chromosomes thus making some of them undetectable. Whether
this asynchrony leads to the elimination of chromosomes causing variation in
chromosome numbers within one specimen plant is not clear. According to
Li & Tu (1947), as cited by LINDSTRÖM, 1965) asynchrony leads to the elimination of chromosomes in a Triticum X Aegilops hybrid, but COLLINS (1968)
showed that the asynchrony of chromosomal replication in Nicotiana hybrids
could not account for somaticinstability. With respect to thelong chromosomes
of the 'Elatior'-begonias no variation in the number of long chromosomes was
found which corresponds with the observations of various authors as LEGRO
& DOORENBOS (1969), MATSUURA & OKUNO (1936, 1943), OKUNO & NAKAI
(1953, 1954) and ZEILINGA (1962), who did not observe variation. On the contrary MEYER (1965), PITON (1962) and SHARMA & BATTACHARRYA (1957, 1961)
found such a variation that they concluded that in the genus Begoniathe occurrenceofaneusomatyis normal. The consistent observation of reduced numbers
of short chromosomes in two 'Elatior'-begonias, 'Riegers Leuchtfeuer' and
'Rose Queen', leads to the conclusion that some elimination of short chromosomes may indeed have occurred.
SUMMARY
Twenty-three 'Elatior'-begonias {Begonia X hiemalis Fotsch) were investigated cytologically. Twenty-one were found to be triploids, each having a diploid number of either 26,27or 28long chromosomes in addition to a consistent
number of 14short chromosomes. Two of these triploid varieties however, had
a reduced number of short chromosomes. The remaining two varieties had
16
Meded, Landbouwhogeschool Wageningen 70-20 (J970)
higher numbers ofchromosomes, the first of these two with a tetraploid number
(52) of long chromosomes and a haploid number (14) of short chromosomes.
The second had odd numbers of long and short chromosomes (56and 7respectively), deviating from any number observed in the previous varieties.
Apostulated asynchrony in themitoticcycles oflong and short chromosomes
respectively, often leading to a less distinct appearance of a few of the short
chromosomes, may account for the occasional finding of reduced numbers of
short chromosomes. Consistent observation of less than 14short chromosomes
in two varieties suggests that some elimination of a few short chromosomes
indeed occurred.
It was concluded that the triploid 'Elatior'-begonias resulted from crossing
tetraploid tuberous hybrids having various numbers (52, 54 and 56) of long
chromosomes and the diploid (2n = 28) species B. socotrana having short
chromosomes. The pentaploid variety 'Flambeau' (2n = 66) probably resulted
from fusion of a tetraploid gamete, which was produced by a tetraploid tuberhybrid, and the normal haploid gamete of B. socotrana.
The observations corroborate a literature reference citing the variety 'Eveleens' Orange' as a hybrid of the 'Elatior'-begonia 'Flambeau' and the triploid
tuberhybrid 'Flamboyant'. A reference citing the 'Elatior'-begonia 'Frau Gertrud Rieger' asthe result of backcrossing the 'Elatior'-begonia 'Riegers Leuchtfeuer' with B. socotrana was repudiated.
Six of the varieties studied had arisen as bud mutations from varieties which
could be studied also. In none of these six the mutation could be attributed to
chromosome loss.
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