FLORIDA STATE HORTICULTURAL SOCIETY, 1959
308
BREEDING BLUEBERRIES FOR THE FLORIDA CLIMATE
though not yet final, is far enough along to
R. H. Sharpe and G. M. Darrow1
When Coville wrote his classic article (1)
on early development of blueberries from the
wild to the cultivated state, brief mention was
made of the ease of crossing the southern
species Vaccinium myrsinites with the northern
highbush species. Both were tetraploid with
48 chromosomes in somatic cells. Attempts to
cross northern highbush with two northern
24-chromosome or diploid species resulted in
complete failures or weak, unproductive plants.
Identification of V. ashei, the rabbiteye blue
berry of northern Florida and south Georgia,
as a hexaploid with 72 chromosomes, and
crosses of it with northern highbush and 24chromosome species have been described by
Darrow et al (2). The 24-chromosome Florida
evergreen species, V. darrowi, was thought to
be of particular interest in breeding blueberries
for Florida because of its blue fruit, drought
resistance and far southern range (3). Suc
cess in combining qualities from the highbush,
rabbiteye, and Florida evergreen species, al1 Associate Horticulturist, University of Florida, and Prin
cipal Horticulturist, U.S.D.A. retired, respectively.
Florida Agricultural Experiment Station Journal Series.
No.
954.
warrant a progress report of this work.
Highbush x Florida Evergreen
Forty seedlings of highbush by V. myrsi
nites were observed at Gainesville in 1952 and
did not look impressive. Growth was badly
delayed, not starting until after April 15,
while adapted kinds were in growth by Febru
ary 15. The limited fruits produced were
black and unattractive. Further breeding may
be useful if the V. myrsinites parents are care
fully selected, but this has not yet been done.
Rabbiteye x Darroufs Evergreen
Blue-fruited plants with a minimum winter
cold requirement for use in breeding appeared
to be best found amongst native plants of the
Winter Haven, Lake Wales, Orlando areas.
Hence, collections were made during the fruit
ing season in 1951 and 31 selected plants were
established at Gainesville. These appeared to
be the 24-chromosome species V. darrowi, so
it was planned to cross them first with V.
ashei to obtain tetraploid plants with 48
chromosomes. These should then cross readily
with the northern, tetraploid, highbush type
to give blue-fruited plants with good drought
TABLE I
CROSS POLLINATION RESULTS BETWEEN V. ASHEI (6x) AND V. DARROWI (2X)
Pollina
Fruit
tions
Set
Seed
••-
lUO
Poor
ashei
1763
375
ashei x V.
darrowi
358
3
V.
ashei x V.
darrowi
565
Beltsville
V.
ashei x V.
darrowi
965
1955
Gainesville
V.
darrowi x V.
ashei
623
1956
Gainesville
V.
darrowi x V.
ashei
1923
1956
Beltsville
V.
darrowi x V.
ashei
5?0
1956
Beltsville
V.
ashei x V.
darrowi
970
Combination
(Seed Parent First)
Year
Location
1953
Gainesville
V. darrowi x V. ashei
195^
Gainesville
V.
darrowi x V.
195^
Gainesville
V.
195*+
Beltsville
1955
No.
of
Seedlings
Hybrid
Total
12
0
2k
3
0
0
17^
1
0
■ 52k
1
1
126
too
305
0
539
U20
115
1
107
0
?69
105
-
—
•
0
0
SHARPE AND DARROW: BLUEBERRIES
resistance and sufficiently low chilling need
309
medium blue, tending to be somewhat darker
than either parent in four of the five seedlings.
The glaucescence of the foliage of the hybrids
is also somewhat less than the parents but
is in the range of other representatives of the
for Florida. Many crosses were made both
at Gainesville, Florida, and Beltsville, Mary
land. An idea of the extent of the work is
indicated in Table I. From over 7,500 pollina
tions only 5 hybrids were obtained. Many of
the other seedlings have been fruited and
found in every respect like one or the other
of the parent species and in no way intermed
iate to indicate they were true hybrids. The
two parent species. The foliage has been very
resistant to mildew and leaf spot infection
under shadehouse and greenhouse conditions
where V. ashei often is seriously attacked. The
hybrids were not field-planted until 1958 and
1959 so their potential height growth is un
known, but they already exceed the V. darrowi
species types are so distinct that these other
seedlings are considered to be apomictic or
from chance or early pollinations before emas
culation. Many of the seeds were obviously
poorly developed, accounting for the poor
stand of seedlings. The 5 hybrids have been
pollinated with northern highbush and other
48-chromosome material with excellent fruit
and seed set, as shown in Table 3.
The 5 hybrids of V. darrowi x V. ashei or
the reciprocal have been vigorous growing
plants with leaves intermediate in size be
tween the parents and nearly evergreen at
Gainesville. Dormancy break has been ex
cellent. Of the three plants obtained from
the 1954 crosses, two have produced no pollen,
£>arent.
Highbush x Darrow's Evergreen
It was thought that northern highbush x
V. darrowi crosses might be more difficult to
make than V. ashei x V. darrowi crosses and
that the seedlings would all be triploid and
sterile. Results proved otherwise, as shown
in Table II. From about 1600 pollinations, 31
selections were made that in subsequent breed
ing have been fully fertile in intercrosses or
in back crosses to northern highbush (Table
III). The nature of the other seedlings ob
tained in these crosses was not fully explored.
Those with V. darrowi as the seed parent ap
peared identical to the parent species. Dis
carded seedlings with highbush as the seed
and the third did not flower until 1958. Hence
these hybrids were first used only as female
parents. The 2 hybrids obtained from the
1955 and 1956 crosses have produced abund
ant pollen and were used readily both as fe
male and male parents in 1959. The fruit of
all the hybrids has required about 110 days
from bloom to maturity in the greenhouse, or
very similar to the parents. Fruit size has
been intermediate, ranging from 11 to 13 mm.
in diameter. Fruit color has been dark to
parent were very late to break dormancy,
failing to start growth before April 15, where
as the selected hybrids usually were in growth
by February 15. It is believed that the latebreaking seedlings were apomictic or from
chance or early pollination, but there is a
possibility that some were triploids.
The selected hybrids have been markedly
slower to go into dormancy in fall than
TABLE II
CROSS POLLINATION RESULTS BETWEEN V .
HIGHBUSH
Combination
(Seed Parent First)
DARROWI
Pollina
Fruit
tions
Set
Year
Location
1951*-
Gainesville
V.
19*
Beltsville
N.H.B. xV.
darrowi
520
1955
Beltsvilie
N.H.B. xV.
darrowi
507
1955
Gainesville
V.
*>
For N.H.B.
abbreviations,
see Table III
NORTHERN
No.
of
Seed
161
darrowi x N.H.B.I
darrowi x N.H.B.
(2X) AND
(tt)
2
Seedlings
Total
17
Hybrid
2
7100
501
2?
110
1*88
111
0
33
135
70
7
310
FLORIDA STATE HORTICULTURAL SOCIETY, 1959
material of straight highbush type. A few
of the hybrid seedlings have been checked
as 48-chromosome types. Their breeding be
havior in 1956 and 1957, as shown in Table
III, indicates fertility with several known 48chromosome types. A few of the V. darrowi
parents have been checked as having 24
chromosomes. It is thought that the V. darrowi
selections probably produced some unreduced
gametes and thus gave rise to fertile tetraploids when crossed with northern highbush.
The hybrids of V. darrowi x highbush and
the reciprocal have intermediate leaf size be
tween the parents with some glaucescence but
much less than V. darrowi. The fruit has
generally required 80 to 90 days from bloom
to maturity in the greenhouse, or about 20 to
30 days less than V. darrowi. (Some northern
highbush varieties require less than 60 days
under field conditions.) The fruit has ranged
from 11 to 14 mm. diameter. Color has been
medium to light blue, about as good as either
parent. Flavors have generally been milder
than the highbush parents.
Crosses of Complex Hybrids
Additional crosses in 1958 by the senior
author were of the same type shown in Table
III, except for being more extensive and
emphasizing more use of northern highbush
parents. About 10,000 seedlings were ob
tained. In 1959 crosses to complete certain
combinations were made. Future crosses will
be planned to utilize some of the material that
has been in the field long enough to judge its
behavior and adaptation. It is hoped that
even better breeding selections of northern
highbush may be available for crosses in 1960
than those first used in 1956 and 1957.
Some of the complex hybrids involving the
three species were fruited in 1959. A few of
TABLE III
SOME RESULTS OF CROSS POLLINATIONS OF COMPLEX HYBRIDS
Number of:
Year
Pollina
Fruit
tions
Set
Combination
Estimated
Seed
Seedlings
1956
(NHB x V, darrowi) x NHB
110
85
1957
NHB-2 x (NHB x V. darrovi)
11*6
136
1956
NHB-2 x NHB
202
121
1957
NHB-3 x (NHB x V. darrovi)
197
192
925
1*00
1956
(V. darrowi x NHB-l)x NHB
10
2
2
2
1957
(V. darrowi x MHB-l) x (NHB x V. darrowi)
l8l
156
11*50
1070
1956
(V. darrowi x V. ashei) x NHB
31
18
150
100
1957
(V. darrowi x V. ashei)-x NHB-3
2k
2k
75
68
1957
(V. darrowi x V. ashei) x (V. darrowi x
41
ko
300
150
1957
(V. darrowi x V. ashei) x (NHB x: V, darrowi) 299
288
1500
800
NHB
Earliblue,
NHB-1
Ga. 23-46 (Dixi x Hildebrandt) pollen was used.
NHB-1)
Blue Crop,
Berkeley, Angola,
1200
1500
1160
702
or Ivanhoe varieties
Hildebrandt was selected in
Georgia
NHB-2
Seedlings of Ga. 23-46 (Dixi x Hildebrandt)
NHB-3
Seedlings of U.S.
39 x U.S.
37 or U.S.
37 self,
seed furnished by Dr.
Darrow.
These selections are from the cross of U.S. 17 (Walker x V. tenellunQx
Earliblue or Berkeley,
thus are essentially only half northern highbush.
Walker is a rabbiteye variety, V. tenellum a 24-chromosome southern species.
HARKNESS: AVOCADO BORON DEFICIENCY
the seedlings had light blue fruit of 14 to 16
mm. diameter, and fairly good quality but
tending to be quite seedy. Hybrids such as the
NHB-2 x NHB shown in Table III broke dor
mancy poorly, but most of those with as much
as one-fourth V. darrowi parentage broke dor
mancy well at Gainesville in 1959. It is im
possible to say at this time if any of the
present seedling material will be good enough
for naming but some individuals appear about
as good as the first commercially-grown varie
ties of northern highbush. A more careful
evaluation will be possible as the bushes come
into heavier fruiting. Since further rapid im
provement can be anticipated in breeding, it is
considered undesirable to be too hasty in re
lease of new varieties until material is ob
tained that compares favorably with the newer
commercial highbush varieties.
Breeding Rabbiteye Blueberries in Florida
The search for suitable parents of the rabbiteye species began in 1948 with observation
of several old plantings in the Gainesville area.
Eighteen selections were obtained from among
the 7000 seedlings examined. These were
propagated in 1949 and tested along with
Myers, Coastal and Calloway varieties and
three unnamed selections from the Coastal
Plains Experiment Station, Tifton, Georgia.
Since then, superior new varieties of this
species have been released and no doubt will
continue to be released from the excellent
program being conducted by the Tifton Sta
tion in cooperation with the U. S. Department
of Agriculture. Many of the named varieties
311
break dormancy poorly at Gainesville after
mild winters, so some breeding has been done
to obtain better adapted selections for Florida
conditions.
From 1952 to 1958, 4000 seedlings have
been fruited at Gainesville, half from con
trolled crosses and the balance from openpollinated seed of some of the better unnamed
Tifton selections. Twenty-three selections have
been saved for further evaluation and possible
increase. All of these ripen fruit relatively late
in the season, usually from late May through
June. A few of the selected plants have shown
excellent dormancy break after the mildest
winters. These were used in a few crosses
in 1959 and about 400 seedlings were ob
tained. Some additional breeding of rabbiteye
selections is planned as soon as present selec
tions can be further evaluated for adaptation
and fruiting characteristics.
Summaby
Crosses have been made between diploid,
tetraploid and hexaploid species to obtain blue
berries with low cold requirement for Florida.
Fertile lines involving all three species
types have crossed readily with each other
and with the tetraploid northern highbush
varieties.
Progress in fruit improvement has
been rapid and satisfactory.
(1) Coville, F. V.,
LITERATURE CITED
1937.
Improving the wild blueberry,
U.S.D.A. Yearbook of Agr.: 559-574.
(2) Darrow, George M., D. H. Scott, and Haig Dermen,
1954.
Tetraploid blueberries from hexaploid x diploid
species crosses, Proc. Amer. Soc. Hort. Sci. 63: 266-270.
(3) Sharpe, R. H., 1954. Horticultural development of
Florida blueberries, Proc. Fla. State Hort. Soc. 66: 188-190.
BORON DEFICIENCY AND ALTERNATE BEARING
IN AVOCADOS
Roy W. Habkness
The alternate bearing test was started in
1951 on two rows of 30 trees each that were
Sub-Tropical Experiment Station
Homestead
Alternate or biennial bearing is a common
characteristic of many avocado varieties. This
article is a report of an experiment designed
to study that behavior in the Booth 8 variety.
It also includes some additional notes con
cerning the effect of boron on avocados.
Florida
No. 983.
Agricultural
Experiment
Station
Journal
Series,
planted in 1940. Each year the fruit from
the south row was picked as soon as mature
while that on the north row was allowed
to remain on the tree two or three months
longer. A weekly record was kept of the drops
from the north row after the south row was
picked.
From 1951 to July 1956 the fertilizer and
spray program was uniform on all the trees.
Then 3 pounds of sulfate of potash magnesia