during this period and often the temperature drops to only 24" C.
Day temperatures rarely exceed 35 C. Afternoon thunderstorms
are a common occurrence although they can be sporadic.
 Over the years, many accessions from around the world have
been evaluated and crosses were made to incorporate heat
tolerant fruit setting with more desirable horticultural traits. In
1983, a yield trial was conducted to evaluate some of the more ad-
vanced breeding lines. The lines tested were:
 1. 7104-1, a small fruited tomato with jointless stem, good
 fruit color and resistance to S and F2;
 2. 7105-1, a large fruited tomato with jointed stem and
 resistance to S and F2;
 3. 7106, a large fruited tomato with jointed stem and
 resistance to S and F2, and Ve;
 4. 7107-SBk, a large fruited tomato with jointed stem, good
 fruit color with uniform green shoulders and resistance to S
 and F2; and
 5. 7108-1, a cherry type tomato, with jointless stem, very
 good fruit color, and resistance to S and F2.
These lines were compared to C1 lid, a small fruited heat
tolerant accession from the AVRDC in Taiwan which has per-
formed well in the past, and 'Walter', a heat sensitive control.
Seed was sown on June 29, and transplanted to the field on
August 8, 1983. A completely randomized block design with
three block of ten plants per plot was used. Plants were spaced 6 cm
apart and staked on raised beds of Eau Gallie sand covered with
plastic mulch. Six harvests were made from October 6 to
November 9, 1983.

Parthenocarpy
 An attempt to combine parthenocarpy with heat tolerant genes
was done at Urbana, Illinois. Cl lid was crossed with
'Severianin,' a Russian variety which has the recessive par-
thenocarpic gene pat-2. Plants were selected for parthenocarpic,
heat tolerant fruit set in the F2 generation, and these selections
were further inbred. Five of these inbreds then were grown with
the two parent lines under the following three environmental
conditions: 1) Bradenton, spring; 2) Urbana, summer; and 3)
Bradenton, summer-fall (Scott and George, 1984). Weather con-
ditions are summarized in Table 1. In general environment 1 was
cool and wet, followed by moderate conditions; 2 was hot and
humid with some moisture stress; and 3 was hot and humid with
no moisture stress. Seed for the Brandenton spring experiment
was sown on January 4, transplanted to the field on February 18,
and four harvests were made weekly from May 10 to May 31,
1983. Seed for the Urbana summer experiment was sown on May
10, transplanted to the field on June 10, and four harvests were
made weekly from August 18 to September 8, 1983. Seeding and
transplanting dates for the Bradenton summer experiment were
as described for the breeding line experiment. Six harvests were
made weekly from October 2 to November 9, 1983. All ex-
periments used completely randomized block designs with four
blocks often plant plots. Spacing between plants was 61 cm at all
locations. Plants were staked in Bradenton but not at Urbana.

RESULTS AND DISCUSSION
 Of the germplasm evaluated, many genotypes with fruit size
>30 g have had good fruit set. One of the most reliable sources of
germplasm has ,been Cl 11d, which is prevalent in many of the
pedigrees of present heat tolerant breeding lines. Cl 1 Id also has
tolerance to bacterial wilt although this tolerance does not appear
to be acceptable under Florida conditions in the summer months
(Sonoda et al., 1978). Progress in development of lines superior
to C 1 1ld has been made, but the job has been difficult, as is evi-
dent by the data from the breeding lines tested in 1983 (Table 2).
Earliness of the small fruited lines was equivalent to C1 lid, and
the total yield of 7104-1 was similar to that of C1 11d (Table 2).


The larger fruited lines-7105-1, 7106, and 7107-SBK-tended
to be later in fruit set than C1 lid (Table 2). Early total yields of
the experimental lines tended to be greater than that of heat sen-
sitive 'Walter,' but differences were not significant for 7105-1 and
7107-SBK. By the end of the season one larger fruited line,
7105-1, had marketable and total yields equivalent to C1 11d and
better than 'Walter.' All lines had a rather large cull percentage,
including 'Walter,' which generally has greater percentages of
marketable fruit during cooler weather. Many culls were due to
catfacing or cracking disorders, which were prevalent under high
temperatures. These results did not inspire a breeding line release
at this point, and further testing of other lines is underway in
1984. Several of the newer breeding lines have a reasonably good
level of bacterial spot tolerance which is a major problem in
Florida during the summer.

 Hybrids between heat tolerant inbreds and larger fruited, crack
 resistant, smooth, heat sensitive, inbreds may be useful to help
 overcome some of the problems in attaining all these
 characteristics in heat tolerant inbreds. In work not presented
 here, it was found that such hybrids had yields comparable to the
 heat tolerant inbreds, but with greater fruit size (Scott andJones,
 1983).

 The use of parthenocarpy offers an alternative approach. Ex-
perimental inbreds, 645 and 646, had yields equal or greater than
Cl 1 Id and Severianin under all three environments (Table 3). In
the spring, fruit set of the C1 11d was relatively low when the
weather was cool and wet, but the other lines set well primarily
because of parthenocarpic expression. Moreover, the percentage
of parthenocarpic fruit set during the early spring harvests when
the cool and wet weather was prevalent was greater than that
shown in Table 3 for the season (Scott and George, 1984). Yields
are less for 645 and 646 during the summer seasons, but not
significantly different than Cl 11d. Line 645 had greater yield
than Severianin at Illinois, due to greater seeded fruit set,
presumably due to presence of some heat tolerance genes derived
from C1 lid.

 The above data indicate the advantages of combining par-
thenocarpy with heat tolerant lines. Fruit set can be enhanced
during both hot and cool, wet weather. Lines which have better
C 11ld type heat tolerance plus pat-2 than 645 and 646 could be
developed, although efficient selection methodology to obtain
both pat-2 and C1 11d type heat tolerance needs to be
elucidated. Much is still unknown about parthenocarpy in
tomatoes. Although pat-2 is a single gene, the expression of this
gene is quite variable. For instance, Severianin was crossed with
the heat sensitive cv. Hayslip, F2's were obtained, and seven selec-
tions were made for good parthenocarpic expresison during the
spring at Bradenton. When these seven lines were assayed for
parthenocarpic set during the summer of 1983, one line set well,
two lines segregated a small percentage of good plants, and four
lines set poorly. Preliminary data in 1984 indicated the good-
setting pat-2 line had early yields comparable to Cl 11d with
greater fruit size, and over 98% of the fruits were parthenocarpic.
Thus, it may be easier to use parthenocarpy without Cl 11d type
heat tolerance to improve fruit set under environments with
temperature and humidity stress. Both approaches in utilizing
parthenocarpy are presently being evaluated. All parthenocarpic
breeding lines, with and without C1 11d type heat tolerance, are
assayed for fruit set under high temperature and rainfall stress in
the summer. Lines which set well parthenocarpically under such
conditions will probably also set well under cold stress. Since cold
stress occurs only sporadically in central Florida, efficient selection
by an alternative method would be difficult.


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