The Long Island Seed Project

Breeding Squash:  Pollinating and Selecting

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The Art of Selection and The Sprawling Zucchini

 August 2, 2007

The Art of Selection

When plant breeders talk about selection, they're generally discussing the merits of a plant from a scientific point of view.  I was asked by a graduate student doing a study on the effect of the Organic Seed Partnership on farm based breeding how my background as a geologist helped me breed new varieties for my farm.  I was at a loss because I think of plant breeding as an art, an almost lost art since it has almost disappeared as a government funded position except for a hand full of public supported breeders at the old "land grant" universities.   And with public supported breeders, it is an art.  I was drawn to geology by the beauty and diversity of the landscape, minerals brought up from the Earth, fossil life imprinted in rock and the desire to learn everything I could in order to understand what I saw.  The same kinds of things draw me to plants.  The beauty and the diversity and the desire to learn everything about them.

A cross between two zucchini with differing characteristics can produce variation in their offspring.  It never fails to cause me some astonishment when I grow the seed of those crosses.  It's like opening Cracker Jacks looking for the surprise at the bottom of the box.  I marvel at the colors, patterns and shape, most are like the unexpected  prize.  As a scientist though, I'm pragmatic and I know that I ought to be better at collecting the data for each of the offspring as I make decisions on what fruit I will collect for seed and which I will discard.  How is one better for my farm environment and my customers than another?  Geology also deals with real world applications such as the planning for geologic hazards and the conservation and sensible extraction of resources for the future.  Such is art and science.

Elizabeth Dyck who has directed the Organic Seed Partnership and works with Public Breeders, Jim Myers from Oregon State University and George Moriarty from Cornell University (above) to teach farmers how they can become more involved in the development of vegetable varieties adapted to their individual farms.  Both Jim and George look critically at each new plant from a cross.  Both take extensive notes on each.  Jim uses a PDA with EXCEL spreadsheet software, George uses index cards taking notes in the field like his predecessor, Professor Emeritus of Plant Breeding at Cornell,  Henry Munger.  Depending on the kind of vegetable, the criteria for evaluation differs.  To develop varieties for organic systems also requires one to look at a different set of criteria than for traditional systems.  Organic farmers and gardeners have a more diverse environment, a different soil biota and a new set of selection parameters since they work without the herbicides and pesticides commonly used in traditional farming.

With expert plant breeders assisting, a group of Long Island farmers participating in the OSP Workshop at Flanders Bay Farm select male and female parents to cross in a diverse planting of zucchini.  The night before, an equal number of mature male and female flowers ready to bloom the next day were taped closed with survey tape (twist ties or masking tape can also be used) to prevent insects from getting at them when they first open the next morning.  You can tell the cucurbits about to bloom because the buds show color the day before. 

On the above photo (left), the female bud (fruit attached) on the bottom is large but does not show color yet and is still two days from blooming, the one above it is ready to be pollinated.  The corolla is removed at the same time the tape is nipped off from both parents the next day and the male is used like a paintbrush to thoroughly coat the female pistil with pollen (right).  Given each row had a different kind of squash: zucchini, delicata squash, pumpkins, acorn squash, round and scallop squash and some bizaar oddities to work with, what guides the decisions you make when choosing the parents of a cross.  Since many squash and pumpkins belong to the same species, Cucurbita pepo, all the diverse squash that had blossoms ties shut could cross to produce viable offspring.  Most participants stayed within the row to preserve the characteristics of a specific kind of squash (find a male scallop squash to cross with this female scallop) and even opted to "self" a particular plant liking the characteristic of the one plant and wanting to preserve the characteristics .  Some noted the vining characteristics of some squash and opted to avoid any potential parent with vining characteristics wanting to maintain compact bush habit.  Most did not cross the aisle (mating pumpkins with zucchini for instance) except in an instance when it appeared that no other tied male blossoms were available!  I jokingly admonished them, "never cross the aisle to another row". 

Of course, I often do.  We have crossed very sweet acorn squash with zucchini to develop a nice sweet summer squash although the bizaar shapes are not about to find public acceptance.  Many immature acorn squash make outstanding zucchini substitutes, something that East End chefs should consider as they put in their orders with the farmer.  Oved Shifress, a Rutger's plant breeder until about 1970 who identified the precocious yellowing, B gene in squash was a strong advocate that Jersey Golden Acorn (which incorporated the B gene) be eaten as a summer squash for the best "sweet corn-like flavor" but the public unfortunately, just never "bought" the idea.

Sprawling Habit:  An unexpected trait from a Cornell Experimental Cross.

How do you select parents and what do you select for?  The sprawling zucchini is a selection from one of the Cornell Crosses.  The initial cross was to impart powdery mildew resistance into summer squash.  It is interesting in that the sprawling character was not anticipated.  But in the F2 generation, unexpected characteristics can appear as genes for various traits segregate.  This  unexpected sprawler starts out with a bush habit, bears it's first fruit at the center (as bush zucchini do) and then sends out laterals in all directions.  These laterals can sprawl several feet and produce a female fruit at almost every node.  The yield and flavor of the sprawling zucchini is considered by many to be superior to bush zucchini.  George Moriarty feels that it is all that extra leaf mass that helps improve the crop.

Vining and sprawling zucchini resulting from intentional or unintentional crossing with other pepo species occurs often.  Many farmers and gardeners would select against a sprawling zucchini.  They take up too much room and interfere with cultivation.  In Israel where hydroponics helps to "make the desert bloom",  this kind of characteristic was viewed as potentially useful.  Now, in hydroponic greenhouses in the mid-east and elsewhere, "sprawling" types of zucchini are trained vertically up support lines in the same way that European greenhouse cucumbers are grown.  In a greenhouse, profit is determined by productivity per square foot.  So, what one person selects against by yanking out of the row, others might flag as an important trait.

Such is selection, partly an art and partly a science.  Seeing new value that others might miss.  The scientist in me looks at yield.  I want a productive plant and my notes on the plants from a cross will reflect the yield.  I'm looking for disease resistance.  On the advise of Michael Glos from Cornell, I made a solution of powdery milder spores.  One handful infected "whitened" leaves (check your lilacs or jerusalem artichokes as a source of pm), one part water and a blender.  Spray over your seedlings.  Select the best of the survivors to plant in the field.  Ah, Darwinian selection at it's best.

I also notice that bean beetles and other insects are at work eating holes in my zucchini leaves and vine borers at the soil level are burrowing the life out of the stem.  Some zucchini are not affected.  "Put them on my note list",  my science training says.  Cross pollinate those squash.  Save the seed.  Plant them out next year (repeat the experiment).  Plant them next to a control (ordinary zucchini).  Observe.

When you hand pollinate a blossom (best in the morning when the flower is fresh and the bees are working), you will want to protect the female flower from other stray pollen that can be carried to the pistil by insects.  George Moriarty passed out the critical supplies at the OSP workshop and explained the technique.  One small paperbag placed around the pollinated blossom, fold corners down to seal the opening around the flower stem and then secure the folds with small bendible metal clips (or use a mini hand stapler).  Use a wire tie twisted around the stem of the pollinated fruit to identify it when the fruit ripens.  I use a piece of plastic survey tape and a "super permanent" ink Sharpie (permanent doesn't mean legible at the end of the growing season) to record the parentage of my cross and tie it around the stem (flower peduncle).

Oh yes, I normally do not bag my blossoms;  instead I tear off all the petals from a pollinated flower and hope that insects will bypass it, also I hope that there is enough pollen from my efforts covering the pistil and stray pollen will not effect the cross.  Lastly, I pollinate late (10 am) and so most pollen has already been cleaned out of the open blossoms by insects.  Does it work for me?  Yes and no.  Under normal field crop conditions I would say that it works pretty good.  In my gardens, it isn't unusual to have dozens of pepo cultivars within a few yards.  Under those extreme conditions, about 10% of my seed from a cross will reflect errant pollen.  If you can't accept that amount of contamination then please bag your blossoms.  For me, I like those odd offspring.  No, I don't know the male parent but sometimes I can guess.  Often,  I find something in an accidental cross worthwhile and for me, it may send me off on a new breeding trip. 

Sprawling Zucchini

Sprawling zucchini is a new plant habit.  It starts out with a bush habit, bears it's first fruit at the center (as bush zucchini do) and then sends out laterals in all directions.  These laterals can sprawl several feet and produce a female fruit at almost every node.  They are, however, more restrained than vining squash.  The yield and flavor of the sprawling zucchini is considered by many to be superior to bush zucchini.   Yield is amazing.

Last Modified:  August, 2007