TOMATO SEED PRODUCTION An organic seed production manual for seed growers in the Mid-Atlantic and Southern U.S

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Copyright © 2004 – 2010 by Jeffrey H. McCormack, Ph. D.
Version 2.9 July 19, 2010
1
TOMATO SEED PRODUCTION
An organic seed production manual for seed growers
in the Mid-Atlantic and Southern U.S.
Copyright © 2004 - 2010 by Jeffrey H. McCormack, Ph.D.
Some rights reserved. See page 16 for distribution and licensing information.
For updates and additional resources, visit www.savingourseeds.org
For comments, suggestions, or distribution information contact:
Jeffrey H. McCormack, Ph.D.
Saving our Seeds
www.savingourseeds.org
Charlottesville, VA 22911
Funding for this project was provided by USDA-CREES (Cooperative State Research, Education, and Extension
Service) through Southern SARE (Sustainable Agriculture Research and Education).

Tomato Seed Production
Copyright © 2004 – 2010 by Jeffrey H. McCormack, Ph. D.
Version 2.9 July 19, 2010
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TABLE OF CONTENTS
Botanical characteristics ..................................................................................................................... 3
Isolation distances ............................................................................................................................... 4
Minimum population size .................................................................................................................. 5
Cultural notes ....................................................................................................................................... 6
Selection ................................................................................................................................................. 7
Methods of seed extraction ............................................................................................................... 8
Insect pests ............................................................................................................................................ 12
Control of seed-borne diseases ......................................................................................................... 13
Seed disinfection .................................................................................................................................. 15
Seed storage .......................................................................................................................................... 15
Distribution and licensing information ........................................................................................... 16

Tomato Seed Production
Copyright © 2004 – 2010 by Jeffrey H. McCormack, Ph. D.
Version 2.9 July 19, 2010
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TOMATO SEED PRODUCTION
BOTANICAL CHARACTERISTICS
Botanical classification of cultivated species of tomatoes:
Family: Solanaceae (nightshade family)
Common tomato: Lycopersicon lycopersicum (formerly Lycopersicon esculentum)
Currant tomato: Lycopersicon pimpinellifolium
The common tomato produces fruits in a large variety of shapes, colors, and sizes whereas the
currant tomato, which has not been domesticated to the same degree, produces red or yellow fruit
approximately 1/4” to 3/8” in diameter. The common tomato will cross readily with the currant
tomato even though the two are different species.
Roots:
Left to grow naturally, tomatoes have a strong taproot which can grow as long as six feet, but
because tomatoes are normally transplanted, the taproot is broken and the plant develops a fibrous
rooting system. Most of the lateral roots develop 2 to 10” beneath the soil surface. The laterals can
grow out a distance of two feet before growing downward to a depth of four feet.
Flowers:
Tomato flowers are borne in clusters that resemble a raceme. Technically they are classified as a
monochasial cyme. Indeterminate varieties of tomatoes have a flower cluster that occurs at every
third internode along the main axis. Indeterminates grow indefinitely provided that environmental
conditions remain favorable. Determinates have flower clusters that occur at every other node, or as
frequently as every node. This growth arrangement continues along the axis until a terminal cluster is
formed and growth of that particular branch ceases. Determinate plants are short-vined, and are
sometimes termed “self-pruning.” Because they have a larger number of flower clusters per length of
vine, the plant tends to fruit and mature a crop within a briefer period of time.
In most varieties of tomatoes, the number of flowers in a cluster is typically four to five. In the
small-fruited cherry and currant tomatoes, the number of flower per cluster can range up to eight to
twelve. One of the more interesting varieties is ‘Riesentraube’ which can have dozens of flowers per
cluster, though not all of these bear fruit.
Pollination and fertilization
:
Pollination is the process of transferring the pollen from the male part of the flower (anthers) to
the female part, called the stigma (pollen-receptive surface of the pistil). Fertilization is the process of
union of the male gamete in the pollen with the egg to form the zygote which becomes part of the
seed. When the stigma becomes receptive to pollen, anthers do not shed their pollen until about 24 to
48 hours later. During this time, cross-pollination can occur, but after the anthers shed their pollen,
the flower is more likely to be self-pollinated. Tomatoes are predominately self-fertilized, but not
exclusively. A large amount of cross-fertilization can occur under the right conditions depending on
the environment, microclimate, and biodiversity in the growing area.
Pollen germinates (develops a pollen tube) when the temperature ranges from 50 to 100
o
F (10
o
C
to 38
o
C). The optimum temperature is 85
o
F (29
o
C). Pollen can be killed at 95
o
F (35
o
C) or above,
depending on the variety. Pollen tube development may also be impaired by high temperatures. Even
at the optimum temperature of 85
o
F (29
o
C) fertilization has been reported to take as long as 50 hours.
Some of the larger-fruited varieties of tomato do not set seed well during periods of extended hot
weather, in the mid-90’s or above, and especially if the night-time temperatures don’t drop below 70
o
F
(21
o
C). Some of the more well-known large-fruited heirloom tomatoes have difficulty setting fruit in
the hot arid Southwest or deep southern states. On the other hand, small-fruited varieties have a
significantly better tolerance to both high and low temperatures, and can be more successfully grown
at temperature extremes.

Tomato Seed Production
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Determinate and indeterminate varieties:
Determinate varieties are short-vined plants on which blossoms and fruit develop about the same
time. Indeterminate varieties are long-vined plants which bear fruit continuously. They should be
caged or staked as noted below. Some varieties are semi-determinate.
Seed:
Tomato seed develops in a mucilaginous gel which has germination inhibitors. During the process
of seed extraction and fermentation this gel is broken down. After the seeds are washed and dried,
the seeds are normally tan or light brown in color with a pubescent covering (fuzz). Tomatoes are
unique among the Solanaceae in that they are the only seed that is pubescent. The number of seeds
per fruit typically ranges from about 150 to 300 or more seeds per fruit.
Tomato seed germinates in the range of 50 to 95
o
F (10
o
C to 35
o
C). The optimum range is 60 to
85
o
F (16
o
C to 29
o
C), and optimum germination occurs at 85
o
F (29
o
C). The Federal standard for
germination is 75%.
ISOLATION DISTANCES
The subject of isolation distances in tomatoes has either been ignored in most seed production
guides, or the information is incorrect. The issue is also controversial. There are a variety of reasons
for the controversy, mostly stemming from a lack of understanding of what factors are important for
determining isolation distances. For an in-depth discussion of this topic, see the companion manual
devoted to the topic of isolation distances. The most important point for the seed grower to
remember is that isolation distances should be understood within the context of the environment in
which the crops are grown. The manual on isolation distances helps the grower understand that
context. In addition, the basic principles of pollination ecology are explained, along with practices
that can be used to modify isolation distances according to your growing conditions. It also contains a
chart of recommended minimum isolation distances, and factors to consider when making
modifications to the recommendations.
One key to understanding isolation distances in tomatoes is knowing that the tomato originated
in South America, largely in the area of Ecuador and Peru where it was (and is) a plant pollinated by
wild solitary bees. During the domestication of the wild tomato, it gradually moved out of its original
geographic range, and out of the range of native pollinators. For this reason, the tomato came under
increasing selection pressure to become self-pollinated. So, although tomatoes have been
domesticated to a great degree, and are now mostly self-pollinated, they retain some of their ancestral
capacity for cross-pollination, depending on the species and variety.
Traditionally, most seed saving guides indicate that tomatoes are self-pollinated. This is
essentially true for modern varieties, but under certain conditions for certain varieties, considerable
cross-pollination of tomatoes can take place. Even a small amount of cross-pollination over a number
of years can lead to the loss of one or more characteristics unique to a variety. Therefore it is
essential that varieties be isolated from each other in order to obtain pure seed.
There are many factors that affect the amount of cross-pollination. These include: (1) variety
characteristics such as flower structure; (2) environmental variables such as wind movement, light
intensity, day length, and carbon-nitrogen ratio; (3) types of pollinating bees present and their
behavior on the blossoms; (4) isolation distance; (5) presence of barrier plants; (6) planting patterns
such as row or block planting; (7) number of varieties; (8) number of plants of each variety; and (9)
regional or bioclimatic factors. Day length can effect the length of the style, as can heat and low
humidity. Long day length, periods of high temperature, and low humidity cause the style to elongate
which in turn favors cross-pollination.
Generally speaking, most modern varieties (introduced after 1950) can be isolated from each other
by a relatively short distance. This is because most modern tomato varieties have a blossom structure
in which the length of style does not exceed the length of the anther cone. This arrangement of flower
structure favors self-fertilization. Older tomato varieties, potato-leaf varieties, and large-fruited,

Tomato Seed Production
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Version 2.9 July 19, 2010
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beefsteak-type tomatoes (including varieties with double blossoms) tend to have an “exserted style,”
meaning that the style protrudes beyond the anther cone, typically by a millimeter or more. This
arrangement of reproductive parts favors cross-fertilization by pollinating wild bees. Some garden
tomatoes have retained some of the characteristics of their wild ancestors. These characteristics may
be found in many cherry tomatoes and currant tomatoes. These types have a blossom structure such
that the style protrudes considerably beyond the anther cone
If you are not familiar with the varieties you intend to grow for seed, you should be conservative
in establishing isolation distances until you know the variety characteristics. Also when growing
different varieties for seed, it is good to get in the habit of examining the flower structure of different
varieties so that you can begin to get an idea of the range of variation and the potential for out-
crossing.
Isolation distances are determined partly on the intended use of the seed. The chart below shows
recommended isolation distances for three different types of tomatoes:
Seed Crop Minimum
for home
use
Minimum
with barriers
Minimum
without
barriers
Comments
Tomato, modern variety 10’ 35’ 75’ Style length, and types and amount
of bees are an issue.
Tomato, large-fruited
heirloom variety
35’ 75’ 75-150’ Style length, flower structure, and
types and amounts of bees are an
issue.
Tomato, wild ancestry 40’ 75-150’ >150’ Style length is a large concern,
especially if wild bees are common.
These distances can be modified on the basis of variables such as the presence of other pollen
sources, or the presence of physical barriers.
Less separation is required if seed is collected only from plants in the center of block plantings. A
tall barrier crop such as ornamental sunflowers is recommended. Pollen-producing crops such as
squash and cucumbers are useful in providing bees with an alternate source of pollen, though this
pollen is available mostly up until mid-day. Borders of perennial flowers are very useful for attracting
bees, especially those flowers that have open, exposed nectaries, for example, members of the
Composite Family (for example daisies and coneflower).
In making decisions about isolation it is important to take into consideration plantings made in
neighboring gardens or farms. If a nearby garden or market garden is a problem for maintaining
isolation, consider donating the same seed variety to your neighbor.
MINIMUM POPULATION SIZE
Plants grown for seed can become subject to “inbreeding depression”. This is a condition where
the genetic diversity of a variety becomes so narrow, or bottle-necked that the variety loses some of its
vigor, fitness, and adaptability as a result of too few plants being saved for seed over one or more
generations. Generally speaking, inbreeding depression is generally not considered an issue in
“selfers” (plants that are self-pollinated). Because tomatoes are predominately self-pollinated they can
be treated as “selfers”, but even selfers can be subject to inbreeding depression if too few plants are
saved for seed.
Because population geneticists have varied responses to the question of the minimum population
sizes needed to prevent inbreeding depression, this topic needs more study. Like the topic of
isolation distances, the devil is in the details. A fuller discussion of the issues will be covered in a
separate manual. The minimum population size depends on the variables involved. That said, there
are some general guidelines. For plants such as tomatoes, no fewer than 20 plants should be grown
for seed, though for a highly uniform (homozygous variety) as few as 12 plants might be required (but
that would be an unusual situation). According to plant breeder John Navazio, as many as 80 to 100
plants should be the minimum population size for most selfers.

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Version 2.9 July 19, 2010
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If you are growing a fairly uniform variety of an established commercial tomato that is available
from a number of sources, 20 plants can be considered the minimum. If you are growing an
uncommon or rare heirloom variety that has more inherent genetic diversity, you should be growing at
least 40 plants, and perhaps as many as 80, if space and resources allow. The question to consider is:
“Who is maintaining the diversity of the stock seed?” If what you are growing represents a small part
of a larger genetic pool, the minimum population size can be smaller. The seed company that
provides the stock seed may be maintaining seed based on a larger population size or pooled lots of
seed or larger grow outs.
CULTURAL NOTES
Sowing seed and handling of transplants:
Sow seeds six weeks (for determinate varieties) to eight weeks (for indeterminate varieties) before
the last frost date in your area. The best planting medium is a sterile seed-starting mix. Good
drainage and aeration are important for starting seeds. Plant seed ¼" deep in shallow flats or cell
packs and maintain soil temperature in the range of 75-85
o
F (24-29
o
C). Under optimum conditions,
most varieties germinate in five to fourteen days, but under less than ideal conditions, germination
may take at least three weeks. When the seedlings have produced four leaves (two seed leaves and
two true leaves), transplant to 3" pots or large cell packs. Seedlings in plastic pots require much less
water than those in peat pots. After transplanting, keep seedlings at a lower temperature at night, 50-
55
o
F (10-13
o
C), to promote earlier flowering in some varieties. Day temperatures should rise to 75-
85
o
F (24-29
o
C) to promote rapid growth. Expose plants to light and air currents as much as possible
to harden the plants and promote stockiness. If fluorescent lights are used, keep the seedlings no
further than two to four inches below the lamps, otherwise seedlings may become leggy. To keep
seedlings stocky indoors, direct a gentle breeze from a low-speed fan toward the seedlings for several
hours a day. Water sparingly, but do not allow the growth to become checked. Fertilize with
complete, soluble organic fertilizer or fish emulsion if leaves become yellow and/or purple. Leaves
with a purple coloration may indicate phosphorous deficiency. Yellowed leaves may indicate nitrogen
deficiency. For transplanting to the garden, average soil temperature at 8 a.m. (4 inches deep) should
be above 60
o
F (16
o
C). To facilitate drought resistance and a larger root mass for nutrient absorption,
set the plants deep in the topsoil to encourage development of adventitious roots that develop along
the stem.
Culture methods (support of vines):
In the Mid-Atlantic and South it is not advisable to grow indeterminate (and some determinate)
tomatoes on the ground for several reasons. Ground culture promotes disease by placing foliage in
close proximity to soil-borne pathogens; interferes with good air circulation around foliage; promotes
fruit-rot (anthracnose); and subjects developing fruits to higher temperatures which could potentially
affect seed development. Plants should be either staked, caged, or trellised (for example, the Florida
weave system). Caging produces the best results, especially for tall indeterminate varieties. Cages
should be 18 to 24” in diameter, and at least 48” tall. Cages can be supported by fastening the cage to
metal electric fence posts, or 48” lengths of rebar which can be purchased at building supply stores.
Spacing of plants:
Recommended spacing distances depend on the variety and the support system used for the
vines. For cage culture, plants should be spaced 24 to 48” apart within the row. Rows should be
spaced three to six feet apart. Most indeterminate varieties are spaced 36 to 42” within the row and
five feet between rows. Closer spacing generally produces higher total yields than wide spacing, but
spacing which is too close may promote disease by interfering with air circulation. Before determining
spacing, you should be familiar with the width and height of the varieties you plan to grow. Certainly
soil fertility, water, tilth, and variety characteristics all have a relationship to the final plant size.
Factors affecting yield:
Too much mulch on the soil in the spring may delay growth by preventing the soil temperature
from rising enough to support active root growth. Starting at the middle or end of June, apply a deep

Tomato Seed Production
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Version 2.9 July 19, 2010
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mulch around plants to help conserve moisture and increase yield. High levels of phosphorus are
necessary to produce good yields, but too much nitrogen added after transplanting will delay
flowering. Pruning and staking increase earliness to fruiting at the expense of yield. Pruning of
determinate varieties should be avoided or kept to a minimum.
Diseases:
Early determinate varieties generally have poor disease resistance, however disease is not usually a
problem until mid-season. Thus disease resistant varieties should be planted for a sustained harvest.
Leaf blight diseases such as early blight and alternaria begin to appear about mid-July, and plants are
more susceptible once fruit production begins. To reduce or prevent disease problems, use resistant
or tolerant varieties and rotate tomatoes to different parts of the garden each year, using a minimum
three-year rotation. Tomatoes should not be grown in soil which has previously been used to grow
peppers, eggplants, or potatoes during the previous three years. Fusarium wilt, a disease caused by a
soil fungus, is common in the Mid-Atlantic region, during mid- to late-season. Where fusarium wilt is
present, a minimum six-year rotation is recommended. Do not plant eggplants, peppers, or potatoes
in wilt-infested soil during the rotation period. Use resistant varieties if space does not permit a six-
year rotation or if there is a history of fusarium in the soil. Avoid planting tomatoes near walnut trees
to avoid "walnut wilt.” Early blight and anthracnose are common in the Mid-Atlantic region, and are
favored by hot, humid conditions. Late blight is more common in inland regions at higher elevations,
especially during the spring and fall. Blossom-end rot is prevented by ensuring an adequate level of
soil calcium and steady moisture. Do not use fungicides. Fungicides may mask important information
about variety performance. When fungicides are absent there is a good opportunity to identify and
select plants which have greater resistance to disease.
Greenhouse and solar greenhouse notes:
Greenhouse-grown tomatoes require pollination for good fruit set: vibrate the blossoms with an
electric toothbrush or tap the flower cluster several times with a pencil. Fans can be used in the
greenhouse to vibrate the blossoms during the wintertime when greenhouses are not vented. The
daytime greenhouse temperature should not exceed 90
o
F (32
o
C), and night temperatures should drop
below 70
o
F (21
o
C), but not lower than 55
o
F (13
o
C). The optimum night temperature is 59-68
o
F (15-
20
o
C). At 40
o
F (5
o
C) some tomato varieties show tissue damage not readily visible to the eye.
Greenhouse tomato pests can be controlled with insecticidal soap up to one day prior to harvest.
Whiteflies, winged-aphids, and leaf miners are attracted to and trapped by sticky yellow traps.
SELECTION
Selecting the plants:
There is usually no need to rogue plants, provided the seed crop is being grown from well-selected
stock seed. However, in dealing with ethnic or heirloom varieties it is not unusual to see more
variability in a seed crop. Many ethnic groups and gardeners maintaining family heirloom seed do not
place the same premium on uniformity valued by the commercial seed trade. Variability in ethnic and
heirloom varieties is not necessarily bad. In fact the variability may be an important source of genetic
diversity. So, in general, you may expect to see more variability in ethnic and heirloom varieties, but
plants that are obviously off-type should be rogued. If you are growing seed of an ethnic or heirloom
variety that is new to the seed trade, the seed company should provide you with some idea of what
type of variation to expect.
Selection of seed plants begins at the seedling stage and continues before the plants have
flowered. Remove any weak plants or those with any off-type foliage before these can pollinate with
any other plants. Pay attention to the foliage of the plant and be aware of any increased or decreased
susceptibility to disease, insects, or environmental conditions. If you see a plant with some unusual or
potentially useful characteristic, you may want to transplant it and isolate it for future evaluation.
Once the plants begin to bear fruit, examine each one for trueness to type. Instead of focusing on
each individual fruit, you should look instead at the overall performance of each plant. Does each
plant have typical fruit color, shape, size, and internal fruit characteristics? If a significant number of

Tomato Seed Production
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Version 2.9 July 19, 2010
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fruits on a plant fail to meet overall performance requirements, the plant should be pulled, otherwise
it is too late for roguing plants once the fruit has been picked.
Selecting fruit on the plants:
In selecting fruit for seed, choose fruit which are true-to-type including typical color, shape, size,
and internal fruit characteristics. In other words, do not use off-type, misshapen, or diseased fruit.
Fruits which are bruised, or fruits which have small cracks are useable for seed, but plants which have
a lot of cracked fruit should be rogued before fruit is harvested, otherwise you may end up selecting
for cracking. It is okay to harvest both early and late fruit, but don't attempt to harvest fruit from
plants which are obviously in stress or decline. During seed processing, keep an eye out for fruit which
has undesirable internal qualities.
WHEN TO HARVEST SEED
Tomatoes should be harvested at the "dead-ripe" stage, but they should not be left on the vine so
long that there is evidence of decay. They should have developed full color, and the fruit wall will
have softened enough to have a slight "give." During very hot weather, I recommend harvesting
tomatoes about two days before they are dead ripe so that they can continue to ripen off the vine in
the shade. If your growing season is shortened prematurely by frost you can harvest the fruit and
allow it to ripen off the plant. Interestingly, seed harvested from immature fruit at the “breaker stage”
(when it shows the first blush of color) will often germinate well, but such seeds will not retain their
viability as well as seed harvested from fully mature fruit. If you do harvest seed from slightly
immature fruit, it should be labeled as such.
In the southeastern U.S. daytime temperatures can climb into the high 90’s. Once fruits are
harvested they should be kept in the shade because the effect of direct sunlight on the fruits for long
hours could potentially raise internal fruit temperatures high enough to damage the seed. When
tomatoes are grown for seed in the Deep South it may be useful to partly shade the plants from
intense afternoon sun. This can be done by growing them near a line of trees that have a large canopy
with few branches on the lower trunks.
Fruits ripening on the vine at temperatures above 90
o
F (32
o
C) may produce lower germination
seed. This problem most likely occurs in varieties that do not have good foliage cover. Normally, this
is not a severe problem and doesn't require corrective action, but may explain lower germination of
seed extracted during periods of hot weather.
METHODS OF SEED EXTRACTION
There are basically three methods of seed extraction: (1) juice and seed extraction, (2) acid
extraction which is not recommended, and (3) extraction by fermentation, which is the preferred
method. Fermentation is the preferred method because it is a natural process that is least harmful to
the seed and can destroy bacterial canker and other seed-borne diseases. Fermentation should be a
controlled process. Though not difficult to do, it can be done incorrectly, in which case the ferment
produces a bad smell and an overgrowth of white fungus which can stain and damage the seed.
Details of the proper procedure are described in the section below.
FERMENTATIVE EXTRACTION
The preferred method for producing commercial-grade seed
The best quality seed is obtained by fermentative extraction. The process basically consists of
breaking or mashing up the fruit into pulp, seeds, and juice, and then pouring the mixture (“mash”)
into a large container where it ferments for a period lasting usually three days. After fermentation is
complete the seed is separated by washing, and then the seed is dried. Though the process is quite
simple there are some important details for performing the process properly.

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Version 2.9 July 19, 2010
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Methods for mashing the fruits:
The first step in extracting the seed is to reduce the fruit to a coarse mash. Before starting this it
is sometimes useful to core the tomatoes first because the cores are heavier, they don’t break down
well during fermentation, and they don’t wash away easily during the washing process. Tomatoes that
have dirt or other debris stuck to the skin should be rinsed off before processing.
There are all sorts of methods that can be used for mashing the fruits, some more fun than
others. Be creative. There are lots of possibilities, and if you develop a new method let me know.
Some suggestions include the following:
 Bucket and masher method (preferred method):
This is the method that I now use routinely. Cut the tomatoes into wedges or sections
and add them to 5-gallon plastic buckets, filling the buckets no more than two-thirds full.
Lids are recommended to keep out fruit flies which can become a nuisance when
fermentation is done indoors. Five-gallon plastic buckets are available at most building
supply stores. Larger containers such as feed troughs are available at farm supply stores.
You may also want to purchase a hand mortar mixer which looks like an oversized potato
masher. This is useful for mashing up the cut-up sections. Alternatively you can mash up
the sections by squeezing them through your hands. If this seems too gross you can use
the mortar mixer to mash them. This secondary mashing method isn’t always necessary if
the tomatoes break apart easily, but the fermenting mash will get a better start and will be
more uniform if the fruits are well broken down at the outset. The advantage of this
method is that it is probably the easiest method for producing small lots of seed ranging
from two ounces to a few pounds. Make sure that you label the bucket with the tomato
variety, and remove old labels when the buckets are cleaned.
Wheelbarrow method:
This method was used by Glenn Drowns, one of our former growers, who used it for
extracting seed of sweet peppers. Fill a wheelbarrow about half-full and chop the
tomatoes with a hoe. Make sure the wheelbarrow is on level ground. The disadvantage of
this method is that the tomatoes may not be equally chopped. This method is for soft-
fruited, medium or large tomatoes: you can’t chop cherry tomatoes with a hoe. The
advantage of this method is that if you are allergic to tomatoes you don’t have to handle
them directly. Though rare, some people can develop rashes or allergies from frequent
contact with tomato fruit and vines. After the tomatoes are chopped, transfer the mash to
a fermentation container.
 Swimming pool method:
I have not used this method, but suggest it as a possibility to explore. This method has
been used successfully by a grower for a small southwestern seed company.
Fill a plastic swimming pool one-third full of tomatoes and step on the tomatoes as
though they are grapes to be smashed into wine. At the end of fermentation, water can be
trickled into the pool at a slow rate (so as to not agitate or float the seeds on the bottom).
The water will clarify, but pulp will need to be scooped or picked out. Alternatively, the
mash can be transferred to 5-gallon buckets or other large containers. This extraction
method can be a great activity for kids. The disadvantage is that the kids will need to
wash their feet and legs thoroughly before moving on to the next variety, and the pool will
need to be thoroughly cleaned. Without thorough cleaning, seeds and diseases of
different varieties can be mixed.
I used a variation of this method when my son was younger. He enjoyed stepping on
tomatoes in 5-gallon buckets. I have since learned that it is not necessary to have a fine
mash for the tomatoes to ferment properly, but it does keep the kids entertained and
involves them in the process.
 Hardware-cloth grater method:
Build a wood frame using two-by-four lumber and mount 1/4", 3/8” or 1/2" hardware
cloth on the frame. (The frame can serve double-duty as a soil sieve.) Place a large tub or
basin under the frame. If the tomatoes are soft, you can rub or grate tomatoes over the

Tomato Seed Production
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Version 2.9 July 19, 2010
10
hardware cloth. It may be necessary to cut the tomatoes first, halfway between the
blossom and stem end.
 Other methods (for processing small seed lots):
The following are other variations to consider, though for small seed lots I find it easy
enough just to cut tomatoes into sections, break them up, and ferment them in quart or
half-gallon jars.
Zip lock bag method:
This method comes courtesy of grower Merlyn Niedens who uses this method for
processing small amounts of seed. Purchase heavy-duty, freezer-quality, quart or gallon-
sized zip lock bags. Write the name of the variety on the side of the bag. Place the
tomatoes inside the bag and crush them. The bag or bags are placed inside a large basin
or 5-gallon bucket. These bags are massaged or squeezed at least twice daily to stir the
ferment. After squeezing the bag several times, partially open the top of the bags so that
gas can escape. Be sure to position or support the bag so the ferment doesn’t spill. When
fermentation is complete the contents are placed in the bottom of a bucket to be washed.
When done, wash out the bag and hand upside down to dry.
Food processor method:
This doesn’t offer an advantage over other methods, except that it can be useful for
cherry or currant tomatoes. It does reduce the mash to a finer texture, but the fine
texture is not necessary for good fermentation.
Use a food processor (not a blender) with a blunt plastic blade and set on a slow setting,
or process with a quick turn on/off motion. This is a very fast and efficient method for
processing small amounts of fruit. Be sure your food processor is equipped with a 1/8”
dull square-edge plastic blade. Do not use a metal blade which will damage the seed. Cut
tomatoes into wedges; drop into the food processor until about half full, and process at a
slow speed until the wedges are broken apart. Caution: although the method works well
and gives good results with little apparent effect on seed germination (when done
correctly), it is not recommended for seed production without first testing to see what
effect it has on germination.
Squeezo® strainer method:
Two products are produced by this method: the juice and the “pumice” which consist of
“dry” pulp, skin, and seeds. The seed is separated from the pumice by washing the seed
with water until the seed is clean. The advantage of this method is that you can save the
juice to drink, but the disadvantage is that it is a slower process, and fermentation isn’t
used (unless you save some of the juice for fermentation). There is a possibility seed may
be bruised by this method, so if this method is used, compare the germination of seed
extracted this way with seed (of the same lot) processed by the bucket and masher
method. Be sure to clean the strainer thoroughly between processing varieties. Seed may
become stuck in small crevices.
Corona grain mill method:
The Corona grain mill can be used to pulp tomatoes that have been cut into sections. The
important point to remember is that the milling plates have to be set far enough apart so
that they do not grind or abrade the seed. A disadvantage of this method is that seed can
become stuck in crevices of the mill plates or grinder and need to be cleaned out, a
concern if you are processing more than one variety.
Adding water to the mash:
If bacterial canker is a problem, it is best to not add water to the mash because dilution of the
mash reduces the effectiveness of controlling canker (see section on Control of Seed-Borne Diseases).
If canker is not a problem, it doesn’t hurt to add a small amount of water, usually not more than 10
percent of the volume of the mash. Adding water makes it easier to stir the mash, and allows more

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circulation of ingredients since the mash is less dense and the rising bubbles have an easier path to
the top of the liquid.
The fermentation process:
After the fruits are reduced to a mixture of sections, pulp, juice and seed, the next step is
fermenting the mash. This happens naturally without any intervention. The combination of naturally
occurring yeast and sugars in the mash is enough to start the process. Fermentation has begun when
small gas bubbles are seen rising from the mash, usually within twelve hours. Fermentation is
complete when gas production slows or stops, when the mucilaginous material around the seed is
digested, and seed has settled to the bottom of the container. A very important step, often not
mentioned in seed-saving literature, is that the mash should be stirred at least twice, and preferably
three times a day. This helps the ferment to work evenly, helps release the seed from the pulp and its
mucilaginous coat. More importantly, stirring prevents the growth of a white scum on top of the
mash. This white scum, often accompanied by a bad smell, indicates the overgrowth of a fungus
which can injure or discolor seeds. If you see this overgrowth you need to stir the mash more
frequently.
Fermentation temperature:
The speed of the fermentation process is largely dependent on the temperature. If the
temperature ranges between 75 to 80
o
F (24 to 27
o
C), fermentation should be complete within 48 to 72
hours. To control bacterial canker, the fermentation should last 96 hours (4 days). This requires a
temperature of about 65
o
F (18
o
C). This long fermentation can cause injury to the seed, such as
premature sprouting. Therefore as a compromise, tomatoes should ideally be fermented at close to
70
o
F (21
o
C) as possible. This may be difficult to achieve in practice during the summer unless
fermentation occurs in an air-conditioned environment or cool basement. At a minimum keep the
fermentation temperature below 80
o
F (21
o
C) because a fermentation temperature (temperature of the
liquid) in the high 80's can cause a 50% loss of germination in 48 hours. A fermentation temperature
in the 90's will cause a loss of germination in the majority of the seed. If fermentation occurs outside,
make sure that it is done in the shade.
When fermentation is complete, the mash has lost its frothiness when stirred, the good seeds have
sunk to the bottom, and much of the pulp has floated to the top.
Washing:
When tomato seed is processed on a large commercial scale, the seed is washed in a shaker
washer or flume. In small-scale seed production where seed is fermented in containers such as
buckets, the first step in washing is to stir the fermented mash, let it settle, and then scoop off much
of the pulp floating on top. Next, water is poured into the mash so that the volume is approximately
doubled. If you don’t add enough water, the specific gravity of the mash may be too high to allow
some of the good seeds to sink. Adding water lowers the specific gravity. This also clarifies the liquid
so that you can see the seed more easily. After water has been added, the mix is allowed to settle
again. The good seeds will sink to the bottom. After the mix has settled, the container is tilted and
the pulp and other debris are poured off the top. The pouring continues until most of the mash is
poured off. Lighter, low-density seeds of poor quality can be poured off with the liquid. This washing
process is repeated until the water turns clear. Typically it takes anywhere from three to six washings.
When the water comes clear, the contents are then poured into a large strainer (held over another
bucket). Excess water is expressed by pressing on the seeds with a large spoon while the seeds are in
the strainer. Next the strainer is flipped upside down over a cloth towel or rag. The seeds fall out into
a pile, and the pile is then spread and flattened with a large spoon until the patty is no thicker than ¼
inch. The towel itself is usually spread over a screen so that air can reach the patty from the bottom
as well as the top. The purpose of the towel is to wick water away as quickly as possible. The patty of
seeds doesn’t need to be turned or stirred provided there is a steady stream of air flowing over the
seeds.
Drying:
Once the seed has been washed and made ready for drying, it should be dried as quickly as
possible without heat. A fan is useful for this purpose. If the seed is not dried quickly it can sprout or

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mold. The seed should be relatively dry to touch within 24 to 36 hours. Drying should take place at a
temperature of less than 90
o
F (32
o
C). Once the temperature reaches 95
o
F (35
o
C) damage to the seed
can occur. For this reason, seed should not be dried in the sun when the air temperature is much over
80
o
F (27
o
C). Seed is best dried in an air-conditioned room with air circulated by fans.
Curing:
Curing is a continuation of the drying process. After the seed has been dried set it aside in a dry
environment with good air circulation to cure for two to four weeks. During this time the moisture
content of the seed is gradually reduced. Seed should be thoroughly cured before being placed in an
airtight container. If curing outdoors, make sure that mice cannot get into the seed.
Milling:
It is usually not necessary to mill seed after washing and drying since there will be little foreign
material with the seed. It may be helpful to screen the seed for size in order to discard small seed.
Seed yield:
Calculating seed yield is an optional step that can be useful for determining seed yields of
different tomato varieties. This is important information if you are a seed grower planning to sell
small lots of seed to seed companies. This only needs to be done the first time you grow a variety for
seed, provided that your growing conditions remain relatively the same from year to year and place to
place. To calculate seed yield, weigh the total lot of tomatoes to be extracted for seed, and then record
this information. After you have extracted, washed, and dried the seed, weigh the dry seed and
calculate how many pounds of fruit are required to produce an ounce or pound of seed. You will also
want to keep a record of the number of plants required to produce a given weight of seed so that in
the future, if you want to produce a pound of seed you will know approximately how many plants you
will need.
An acre of tomatoes raised for seed may yield an average of 35 to 160 pounds of seed depending
on the variety, the density of the planting, the amount of crop saved for seed, fertilization efficiency,
and growing conditions. One hundred pounds of tomatoes will yield approximately 4 to 10 ounces of
seed, but this number is strongly influenced by the fruit size, variety, and growing conditions. Seed
size and weight varies depending on variety, and averages about 11,480 seeds per ounce. The Federal
germination standard is 75%.
Labeling:
It is easy to lose a good batch of seed if you have not labeled your seed at every step from
extraction through drying. Never assume that you will remember which variety is which. The label
should travel with every step of the process from start to finish.
INSECT PESTS
An important thing to remember about insect pests is that just because an insect is feeding on a
plant doesn’t necessarily mean that there will be an adverse effect on yield. Some plants can
withstand quite a bit of defoliation without serious consequences, so a zero-tolerance policy is not
advocated. Instead, a policy of damage assessment based on cost-benefit is more ecologically
sustainable. Cost-benefit analysis involves awareness of what role the pest is playing in the ecosystem.
Generally speaking, if you have created a growing area with rich biological diversity, your pest
problems are likely to be minor.
Tomato hornworms (Protoparce sexta and Protoparce quinquemaculata):
Tomato hornworms can be controlled by Bacillus thuringiensis, though in most cases it is not
necessary to use this unless the outbreak is severe. Handpicking hornworms early in the season often
provides sufficient control. Incorporate biological diversity into the growing area. This encourages the
activities of small parasitic wasps to lay their eggs on hornworms. As the wasp larvae develop inside
the hornworm, the hornworm becomes lethargic or immobile, and shortly thereafter, the young wasps

Tomato Seed Production
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Version 2.9 July 19, 2010
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emerge from the caterpillar. Hornworms with the white egg cases of parasitic wasps on their backs
should not be destroyed because the wasps will hatch out and parasitize other hornworms in the
garden. It is worth noting that hornworms hatch out into night-flying sphinx moths which are
important pollinators of some flower and herb crops.
Fruitworm (Heliothis armigera):
Fruitworm, also known as the corn earworm can be controlled by Bacillus thuringiensis. Tomatoes
with thick skins, especially cherry tomatoes are much more resistant to fruitworm than varieties with
a thin skin.
Flea beetles (Epitrix cucumeris):
Flea beetles are rarely a serious problem. A simple control measure is to keep flats of tomato
seedlings several feet off the ground because the flea beetles have a more difficult time reaching the
plants.
CONTROL OF SEED-BORNE DISEASES
Tomatoes are prone to a number of diseases, many of which affect yields noticeably. There are
over 20 bacterial and fungal diseases which can affect tomatoes, plus others caused by insects, or non-
parasitic diseases, also called physiological diseases (for example, blossom-end rot). Sometimes more
than one disease may be present at a time. As a seed grower, the diseases that are of most concern
are those diseases which can be carried in the seed or on the surface of the seed coat.
Basic sanitation and prevention is always the first step. To control seed-borne diseases, it is
important to practice crop rotation, to clean up and compost all plant residues, to maintain adequate
nutrition, and to select and wash fruit before collecting the seed. Seed crops should be planted early
in the season, rather than late. By planting early in the season a seed crop may be produced before
the onset of warm humid conditions which favor fungus diseases. Plants which show disease should
be rogued as quickly as possible to minimize disease spread. Seed should be collected only from
healthy plants. Fruit which shows obvious signs of discoloration, fungus growth, mosaic patterns, or
other abnormal conditions should not be used for seed (unless there is a risk of losing the variety).
The ground should be mulched under the plants. This prevents rain from splashing disease spores
onto the plant.
Seed growers should be aware of several seed-borne diseases which may be carried on tomato
seed. The most important diseases for the Mid-Atlantic and Deep South are those listed below:
Bacterial canker (caused by the bacterium, Corynebacterium michiganense):
This bacterial disease is not widespread but can be destructive, and it is more common in
southern states. As a seed producer, you should be familiar with the symptoms. Fruits infected with
canker will show "bird's eye" spots. These are dark rough spots (usually tan or brown, about 3/16"
(3mm) in diameter), surrounded either by a water-soaked area, or white halo. Symptoms on foliage are
evident as an upward curling of leaves which turn brown and wither but do not fall off. Cankers may
develop at leaf nodes and spread downward. The cankers first appear as light streaks which darken
and crack; later small cankers may form along the length of the crack. The pith of the stem may
appear yellow and mealy. Canker disease can be eliminated by extracting the seed with fermentation.
To destroy canker by fermentation keep the temperature at or below 70
o
F (21
o
C) for a minimum of 96
hours. Canker may also be destroyed by acetic acid treatment. Moist, just-extracted seed is soaked
for 24 hours in a 0.8% solution made from pure acetic acid (1 ounce acetic acid per gallon of water). If
dried seed is being treated, use ¾ ounce acetic acid per gallon of water. If acetic acid is not available it
may be possible to obtain a 0.8% solution of acetic acid by diluting white cider vinegar (5% acid
strength) with 5-¼ parts water. (Note: I am not certain that white cider vinegar is as effective as pure
acetic acid diluted to 0.8%.) After acetic acid treatment rinse with water and dry as soon as possible.

Tomato Seed Production
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Tomato (tobacco) mosaic virus:
Tomato mosaic is most often seen on greenhouse-grown tomatoes and sometimes field-grown
tomatoes. The most common symptom is a mosaic or mottling of the leaves which shows as irregular
patches of yellow or light green mingled with green. Leaves may be distorted, blistered, curled,
dwarfed, or elongated like shoe strings, depending on the strain of the virus. Infected fruit may not
show any symptoms, or may show some internal browning or discoloration. Tomato mosaic virus may
be prevented by keeping smokers out of the garden (cigarettes may carry the virus), by dipping your
hands in milk each time you handle another plant (milk inactivates the virus), and by using disease-
free seed. I never let smokers into our seed gardens or into our seed packing facility – no exceptions!
Tomato mosaic virus doesn’t get into the seed embryo but is carried on the seed coat and is
difficult to remove or inactivate. Seed harvested from infected plants may produce up to 3% infected
seedlings. The virus can be attenuated or inactivated by storing dry seed at room temperature for
several months to a year. Seed which has been stored several months will usually produce normal
seedlings, though the virus may still be present in the seed coat. In addition to dry storage, the virus
may also be inactivated by treating seed with 10% trisodium phosphate for 10 minutes followed by 3
water rinses lasting 5 minutes each. Planting the seed directly without later transplanting will also
reduce the incidence of the disease.
Fusarium wilt (caused by the fungus, Fusarium oxysporum f. lycopersicae):
This fungal disease is fairly widespread in occurrence, and more prevalent in southern and warm
coastal states. Wilting is the most obvious symptom. Typically one stem may wilt, yellow, and die
back at the top, presenting a flag-like appearance, or yellowing and wilting may occur only on one side
of a leaf midrib. The infected stem may die back or wilt severely before other stems show infection. If
you suspect fusarium wilt, it can be confirmed by cutting the stem in cross section. The vascular
tissue of the stem will be discolored, typically showing as a brown ring. Plants showing fusarium wilt
should be pulled and the vines should not be composted. Instead they should be discarded in the
trash or a location far away from the growing area. The disease is fairly persistent in the soil, and
plants in the tomato family (Solanaceae) should not be grown in fusarium-infested soil for at least six
to eight years. Control measures include paying strict attention to crop rotation and growing wilt-
resistant varieties. Hot water seed treatment can be an effective treatment in some instances.
Anthracnose (caused by the fungus, Colletrichum phomoides):
This fungal disease is a fruit rot found on uninjured ripe tomato fruits, and is common in the Mid-
Atlantic and southern states. Another name for this disease is called “ripe-rot”. In the early stages of
infection, lesions on the fruit appear as small, sunken, circular spots that appear as water-soaked
indentations in the skin. These gradually grow larger, up to about ½” in diameter, and develop a dark
center because of the black fungus under the skin. The disease becomes more prevalent, especially in
August during hot and rainy weather. The disease organism is prevalent in the Mid-Atlantic and grows
best at 80
o
F (27
o
C), but it doesn’t grow above 95
o
F (35
o
C) and for that reason isn’t as much a problem
in the Deep South. Tomato varieties that are subject to defoliation by other diseases are also more
susceptible to anthracnose. Lesions also appear on the stem and foliage, but are easily overlooked.
These stem and leaf lesions may serve as infection sources for the fruit. This is why it is important to
remove plant debris at the end of the season. A crop rotation of at least four years is recommended.
Early blight (caused by the fungus, Alternaria solani):
Early blight is fairly common in the Mid-Atlantic, especially during periods of frequent rain.
Infection can occur in the seedling stage, but is most commonly observed on the older leaves of
established plants, frequently after fruits begin to set. Symptoms develop as dark spots with
concentric rings. The rings spread to surrounding tissue and as the infected leaves die, they become
dry and papery. In addition to causing a decrease in yield, the disease can be carried on the seed. The
disease is promoted by heavy dews and frequent rainfall. Maintaining good air circulation around the
plants can be helpful, as well as mulching the soil to prevent soil splashing of spores onto the leaves.
A minimum two-year rotation and removal of crop residues is helpful in controlling the disease. The
disease may be seed-borne, but proper fermentation of harvested seed helps to control the disease.

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Version 2.9 July 19, 2010
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SEED DISINFECTION
In most cases no seed disinfection treatment is recommended for disease control. Proper
fermentation of extracted seed will destroy canker and some other fungus diseases. Long-term dry
storage will attenuate tomato mosaic virus. If you find it necessary to harvest fruit from plants
affected by diseases such as wilts, blights, etc., and are concerned about the possible transmission of
disease you can use the following general seed treatment. Prepare a 10% solution of commercial bleach
and soak thoroughly dried seed for 10 minutes with frequent stirring. Pour off the bleach solution and
follow with three, 5-minute water rinses. Dry the seed as soon as possible. This treatment may have a
small adverse effect on germination. Note: any seed which has been treated with a chemical, no
matter how mild, should be labeled to that effect. In fact, Federal seed law requires that if seeds are
treated with any substance they must be labeled as such. Also, any seed which you suspect might be a
carrier of disease should be labeled. This is especially important if you exchange seed with others or
grow seed commercially.
Seed disinfection and organic certification:
Seed can be disinfected by hot water treatment. The process involves immersing the seed in water
hot enough to kill the pathogen, but not so hot that it damages the seed. This process is discussed in
a separate manual dealing with control of seed-borne diseases. Check with your certifier to assess the
different seed disinfection options available.
SEED STORAGE
Details of seed storage are available from many sources and are the subject of another manual in
this series. Just the basics are covered below.
Long-term storage:
It is very important that seed be thoroughly dry. Freshly harvested seed should be cured for a
minimum of three to four weeks before placing in long-term storage. At least one week before the
seeds are placed in airtight containers, they should be transferred to an air-conditioned or heated
room or other low humidity environment before being placed in a jar with a rubber-gasketed lid.
Thereafter the seed may be transferred to the refrigerator or other cool environment. Before opening
the jar, always allow the jar to warm up to room temperature. Try to do this on a dry day so that
humid air is not introduced to the jar. Note: never store seed in a closed container unless the seed
has been dried thoroughly first .
Short-term storage:
For short-term seed storage, it is not necessary to store seed in airtight jars. Seed can be stored in
large envelopes, paper bags, cloth bags, or other non-airtight containers. Porous containers are not
recommended for storing seed for long term unless the surrounding air remains cool and dry. Zip
lock bags and most plastics allow water vapor to pass through and therefore these materials are for
short-term seed storage only.
SHIPPING SEED
Just the basic information is included here. Before seeds are shipped, there should be labels on
both the inside and outside of the seed containers. Paper bags should be triple bagged. If a seed
container breaks open and mixes with other seed, the seed will be worthless. Any shipment of seeds
should be able to withstand a minimum ten-foot drop without damage to the container or its contents.

Tomato Seed Production
Copyright © 2004 – 2010 by Jeffrey H. McCormack, Ph. D.
Version 2.9 July 19, 2010
16
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