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The OSP made a small number of seeds of this interesting second
generation lettuce cross from USDA-Salinas to a number of organic
farmers several years ago. Last year we multiplied the lettuce
seed on our farm (a simple job) and this year we're selecting for
vigor, taste, texture and bolt resistance. You can see some of
the diversity in the plants . Apparently, the seed was been
sitting around in Salinas, California for a while without generating
much interest since this is clearly not a lettuce for distance
shipping. It is; however, resistant to leaf miners and combines the
flavor of the old French heirlooom with the texture and heat tolerance
of Salinas. And for that reason, the folks at Salinas thought
that it might be of interest to the organic farming community and
passed it on to OSP and through the partnership, to us.
These are the four primary phenotypes that appeared in the F3 of the
Salinas cross. Fine flavored and with a definite bolt resistant
population, we are enjoying this loosehead lettuce which has enough of
a heavy texture to please my finnicky niece.
We always grow a few types of lettuce. I've grown different varieties
side by side in hopes that some would just cross but they never
do. So how is it that the professional breeders develop new
Lettuce is in a group of plants called composites, like daisies,
sunflowers, zinnias, dandelions and scores of other plants. They
produce a flower which technically is actually better called a "head"
since it consists of many flowers or florets. Some of those florets can
be ray flowers, they are arranged in a concentric way around the
outside of the head as a single circle of petals each attached to the
ovary or fruit which ripens to contain a single seed. Ray flowers may
extend inward from their outer ring to a series of rings which gives
the flower head a distinctive doubling effect (double marigolds, for
example). Inside there may be disc flowers, often dozens crammed
together making up the central part of the head. These little florets
don't have the conventional showy petal attached like the ray flowers
do but they are attached, each to an ovary which can also mature into a
single seeded fruit called an achene. Unless you eat sunflower seeds
you probably won't notice that seed of a composite like lettuce is
actually contained in a shell-like fruit.
Lettuce flower heads are more like a dandelion than a sunflower and
consist of a multitude of densely packed ray florets which open at the
same time. As the florets open, the central stigma pushes through a
crown of stamens and automatically is pollinated. Therefore, lettuce
tends to be self pollinating. In fact, hand crossing lettuces is as
tedious as hand crossing peas. There are some very effective insect
pollinators that can cross lettuces, I am told. Therefore, you will
want to separate varieties by a few meters if you are growing seed
crops and want to maintain the purity of a variety.
So how does one hybridize two lettuces to combine the characteristics
and have a new pool of traits to select from?
That was a quiestion that I asked George Moriarty of Cornell who has
worked with lettuces. He explained that what he does is find an
unopened flower bud on the lettuce that will be the female
parent. This bud has to be within a day of opening.
Remember that the bud opens into a head of many small flowers and that
the stigma of each tiny flower pushes through the stamens above which
the pollen. Cut off the top half of the flower bud (which removes
the male stamens). Then find a fresh, open flower from your selected
male parent. Place a drop of water on the remaining exposed base
of the female flower head and then swab the male into the water to
release the pollen into the film of water. Tag the blossom.
This special blossom with all your hand labor is the one that you will
watch ripen and produce seed. Each of the dozen or so florets on
the head will produce a seed.
The seed is now F1 hybrid. Actually, there is a good possibility
that some stray pollen contamination was introduced and so not every
seed in that head will be a hybrid. George says though, that the
hybrid vigor of the F1's will be apparent when the seed germinates and
that you should select those to grow out.