'Dark Star' Zucchini John Navazio, PhD and Bill Reynolds, Farmer
Bill Reynolds and Donna Ferguson have marketed high quality organic zucchinis to the San Francisco market for a number of years. The preferred zuke for this market is dark green and not more than 8 inches long with a 2-inch diameter. Bill and Donna have relied heavily on the favored commercial variety for this market, ‘Raven’ from Rogers/Syngenta. However, they often had problems accessing this variety in the 1990s.
In at least two years there was a shortage of ‘Raven’ seed (presumably a Rogers production problem) and as is often the case when this occurs the seed was prorated to the distributors who in turn only sell to their largest customers. This often leaves smaller farms like Eel River with no seed of that particular variety. Over the years Bill and Donna also noticed that on occasion some of the seed lots of ‘Raven’ were erratic, with a greater number of off-type plants than would usually be expected from a major seed production and research company. These factors led them to try the older standard open-pollinated (OP) variety ‘Black Beauty’ in the hopes of finding a dependable, dark skinned, market class zucchini.
They found ‘Black Beauty’ to be typical of many OP vegetable varieties of cross- pollinated species that lack continuous selection. Although it is definitely a dark green type with many good features that meet their market criteria, they found too much plant to plant variation to make it an efficient, commercial variety for their market. Even though Black Beauty had a relatively high yield, they realized that they would need at least 3 to 4 times the number of plants to choose from when compared to ‘Raven’ to supply their needs for Grade A zukes. The obvious flaws in many fruits included thin necks, bottle shapes, curved shapes, and light to medium green color. Plant architecture in many of the plants was also a hindrance. Many ‘Black Beauty’ plants have “busy” or closed canopies, where too many leaves emanate from the main stem making it hard to see the fruit when cruising the patch and making it hard to harvest without scratching the fruits on the spines of the leaf petioles (stems). This is in contrast to most modern hybrid zukes that have fewer leaves and an “open” canopy that allows one to easily locate and harvest the fruit. Also the angle in which the fruit grow outward from the stem is often at a low angle towards the ground, making it harder to harvest and more easily damaged in the soil.
Initial Breeding Effort Seeking a variety that combined the best qualities of ‘Raven’ with the best qualities of ‘Black Beauty’ Bill started a breeding project. Starting with a large production field of both ‘Black Beauty’ and ‘Raven’ Bill started to save seed of the best plants from each variety. As zucchinis (Cucurbita pepo) are a cross-pollinated species much of this seed was a result of crosses between the two varieties. For the next 3 to 4 years Bill saved and replanted seed from the best plants derived from these crosses, mixing the seed from the best plants each year and replanting it the following spring. This technique, known as “mass selection,” has merit in that it retains much of the initial genetic variation that went into the cross that may be used in future generations to adapt the material to different challenges, environments, and markets. The disadvantage is that it is a slow, inexact breeding method and it can take many years to get a variety with any semblance of uniformity.The reason that mass selection is slow is that you don’t know the traits of the male parent or the recessive genetic traits of the female bearing the fruit you are selecting for seed. After four years this work did result in a new open-pollinated variety, which Bill and Donna named ‘Black Eel’. Despite its lack of uniformity it has a good percentage of dark green, well-proportioned fruits. ‘Black Eel’, which is available through Seeds of Change (SOC), has had good success as a variety for home gardeners. However, SOC soon realized that if they were to offer a zucchini that was commercially viable for the market farmers seeking organically grown seed, that they would have to ratchet up the breeding effort to produce a variety with the best traits of ‘Black Eel’ without the variability. SOC decided to fund a Participatory Plant Breeding project bringing together Bill and Donna’s advanced agronomic and market knowledge of zucchini culture with my expertise in breeding cross-pollinated vegetable crops for organic production methods.
Participatory Plant Breeding In the summer of 2003 we decided that in order to produce a more uniform, market class zuke a breeding technique known as “recurrent selection” would be coupled with Bill and Donna’s knowledge of market class zucchinis. Over an acre of ‘Black Eel’ was planted with border rows of ‘Raven’ as a means of comparison. The first step was for Bill and Donna to identify approximately fifty very good ‘Black Eel’ plants that had as many of the aforementioned desirable agronomic and market traits as possible and then self pollinate each of those plants. Knowing that very few plants in a field of this size would have a combination of all the sought after traits we agreed that plants with good examples of most traits and no serious flaws would be considered for a self-pollination.
Over 50 self-pollinations in the ‘Black Eel’ population were attempted by Bill and Donna but as many breeders come to realize, humans are not as successful at making pollinations as bees or other insect pollinators. Of the hand pollinations made 26 were successful and most of these produced ample seed. This seed was harvested, cleaned, and dried separately from each fruit and was placed into 26 individual envelopes for planting the following season.
2004 Progeny Testing In the summer of 2004 seed from each envelope was planted into a single “full-sib” progeny row. Hence the plants in each row were “full siblings” from single self-pollinated plants in 2003. By the time the plants in these 26 rows were fully fruiting I received a distressed call from Bill wanting to know what had gone wrong. It seems that at least 8-10 of the progeny rows had mostly vining plants (when he believed he had almost completely eliminated that trait.). Other progeny rows had a preponderance of “bushers,” while others had many bulbous fruit, both at a much higher than average rate. There were even a few plants scattered through the 26 rows with yellow summer squash fruit. He couldn’t believe his eyes and he was truly worried that he’d done something wrong. I assured him that in fact this was the perfect outcome and that this was precisely why we selfed the plants. We were revealing the genetically recessive traits that often are “hidden” behind the more prevalent genetically dominant traits that usually are the distinguishing characteristics of the variety. This recurrent selection breeding method with progeny testing and selection is indeed a way to reveal the full-sib families with a preponderance of deleterious (unwanted) recessive traits. “Full-sib families” are the off-spring population of a self pollinated plant. Not only are you revealing more deleterious traits per population through the selfing step and eliminating those plants, but you are also able to eliminate all the members of a full-sib family (even good looking plants) if there is a preponderance of poor plants in that family. Why? Because any closely related plant, even a good-looking plant, undoubtedly holds some of the same poor genetics behind a veneer of dominant genes.
The next step was for Bill and Donna to harvest the plot as a normal commercial field for 2 to 3 weeks to really get to know the rows and the kind of uniformity, shape, and color of fruit as well as the plant characteristics mentioned earlier. By the time I arrived 3 weeks later Bill and Donna had identified 4 to 5 five rows out of the 26 with both superior fruit and superior plants. They showed me the undesirable plant types first with viners and bushers and we all agreed these had to go. Then they showed me the in between rows with some favorable plants but enough fruit or plant flaws that it was understood they would be tilled under as well after a couple more commercial harvests. Then I witnessed the 5 best rows; each exhibited market quality fruit on open, bush plants, fruits borne at a good angle, and some even had very few spines on the petioles (leaf stems.) These rows had at least 70% good plants and the ~30% less favorable plants weren’t overly bad. Upon further inspection one of the 5 rows was not up to the standard. The decision was made to till the other 22 rows in the field and only allow the best 4 to intermate for the next generation of selected seed.
In summary, the 22 non-selected rows were tilled under. Of the remaining 4 selected rows, about 30% of the poorest plants were pulled and destroyed. Lastly all the fruit from the remaining plants in the four selected rows was harvested no matter the size so there would be no chance of a pollination event from the plants that had been eliminated. The best plants in the four rows were then allowed to intermate openly and set fruit. This method furthered the breeding progress by allowing for evaluation of the previous generation and intermating of the best offspring for the next generation in a single season. The intermated seed was harvested from the 4 rows separately into 4 bags. The idea was there would still be shared family characteristics within each row despite the out-crossing to the other rows. Indeed, the out-crossing was by design to reinvigorate each full-sib family with some genetic variation from the other elite rows after the selfing event of the previous generation. With this out-crossing between progeny rows these 4 families became half-sib families as the pollen source was unknown.
2005 Comparisons: ‘Dark Star’ Emerges In 2005 the seed from these 4 half-sib family rows was planted in two large blocks along with the original ‘Black Eel; and ‘Raven’. Each variety had 4 rows in each of two locations or replications [“reps”] in the field. Bill and Donna harvested this field as a crop while scrutinizing it for all of the agronomic and fruit traits heretofore mentioned. While all 4 families had a high percentage of superior plants and superior fruit only one of the 4 families really started to emerge as a consistently excellent type through the scrutiny of multiple commercial harvests. The half-sib family that traced back to hand pollination #41 (of the original 50+ attempted) was truly superior with an excellent plant type with virtually no bushers, a good angle for the fruit set, and a low degree of petiole spines. It also has a great fruit type that is dark green, cylindrical, and has a good length to diameter ratio for a uniform harvest. It was decided that this family was the only one worth advancing and so the other 3 families plus the comparison rows of ‘Black Eel’ and ‘Raven’ were tilled up with only the two blocks of #41 remaining in the field. These rows of #41 were scrutinized thoroughly. Any plants within this half-sib family with flaws was pulled and destroyed. Very few flawed plants were found. All remaining plants were allowed to intermate to produce seed of the prototype variety ‘Dark Star’ to be tested in 2006.
2006 Testing of ‘Dark Star’ Starting with a winter zucchini crop in Baja California, ‘Dark Star’ is being tested in several locations in 2006 to see if it is of commercial quality. In Baja it was planted in large blocks in an organic production field in January. Bill was able to see it over the course of the winter season and found it to be better than several standard hybrid zucchini varieties grown in nearby fields. It is also being tested at the Seeds of Change Research Farm in New Mexico and at Prescott College’s Wolfberry Farm in Arizona. Bill and Donna are producing a large crop for seed at their farm on the Black Eel River in Shively, California and depending on the percentage of off-types found in the population they will decide with Seeds of Change whether it is ready for release for the 2007 season.
John Navazio Organic Seed Alliance August 16, 2006
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They found ‘Black Beauty’ to be typical of many OP vegetable varieties of cross- pollinated species that lack continuous selection. Although it is definitely a dark green type with many good features that meet their market criteria, they found too much plant to plant variation to make it an efficient, commercial variety for their market. Even though Black Beauty had a relatively high yield, they realized that they would need at least 3 to 4 times the number of plants to choose from when compared to ‘Raven’ to supply their needs for Grade A zukes. The obvious flaws in many fruits included thin necks, bottle shapes, curved shapes, and light to medium green color. Plant architecture in many of the plants was also a hindrance. Many ‘Black Beauty’ plants have “busy” or closed canopies, where too many leaves emanate from the main stem making it hard to see the fruit when cruising the patch and making it hard to harvest without scratching the fruits on the spines of the leaf petioles (stems). This is in contrast to most modern hybrid zukes that have fewer leaves and an “open” canopy that allows one to easily locate and harvest the fruit. Also the angle in which the fruit grow outward from the stem is often at a low angle towards the ground, making it harder to harvest and more easily damaged in the soil.
‘Black Eel’, which is available through Seeds of Change (SOC), has had good success as a variety for home gardeners. However, SOC soon realized that if they were to offer a zucchini that was commercially viable for the market farmers seeking organically grown seed, that they would have to ratchet up the breeding effort to produce a variety with the best traits of ‘Black Eel’ without the variability. SOC decided to fund a Participatory Plant Breeding project bringing together Bill and Donna’s advanced agronomic and market knowledge of zucchini culture with my expertise in breeding cross-pollinated vegetable crops for organic production methods.
In the summer of 2003 we decided that in order to produce a more uniform, market class zuke a breeding technique known as “recurrent selection” would be coupled with Bill and Donna’s knowledge of market class zucchinis. Over an acre of ‘Black Eel’ was planted with border rows of ‘Raven’ as a means of comparison. The first step was for Bill and Donna to identify approximately fifty very good ‘Black Eel’ plants that had as many of the aforementioned desirable agronomic and market traits as possible and then self pollinate each of those plants. Knowing that very few plants in a field of this size would have a combination of all the sought after traits we agreed that plants with good examples of most traits and no serious flaws would be considered for a self-pollination.
In the summer of 2004 seed from each envelope was planted into a single “full-sib” progeny row. Hence the plants in each row were “full siblings” from single self-pollinated plants in 2003. By the time the plants in these 26 rows were fully fruiting I received a distressed call from Bill wanting to know what had gone wrong. It seems that at least 8-10 of the progeny rows had mostly vining plants (when he believed he had almost completely eliminated that trait.). Other progeny rows had a preponderance of “bushers,” while others had many bulbous fruit, both at a much higher than average rate. There were even a few plants scattered through the 26 rows with yellow summer squash fruit. He couldn’t believe his eyes and he was truly worried that he’d done something wrong. I assured him that in fact this was the perfect outcome and that this was precisely why we selfed the plants. We were revealing the genetically recessive traits that often are “hidden” behind the more prevalent genetically dominant traits that usually are the distinguishing characteristics of the variety. This recurrent selection breeding method with progeny testing and selection is indeed a way to reveal the full-sib families with a preponderance of deleterious (unwanted) recessive traits. “Full-sib families” are the off-spring population of a self pollinated plant. Not only are you revealing more deleterious traits per population through the selfing step and eliminating those plants, but you are also able to eliminate all the members of a full-sib family (even good looking plants) if there is a preponderance of poor plants in that family. Why? Because any closely related plant, even a good-looking plant, undoubtedly holds some of the same poor genetics behind a veneer of dominant genes.
The next step was for Bill and Donna to harvest the plot as a normal commercial field for 2 to 3 weeks to really get to know the rows and the kind of uniformity, shape, and color of fruit as well as the plant characteristics mentioned earlier. By the time I arrived 3 weeks later Bill and Donna had identified 4 to 5 five rows out of the 26 with both superior fruit and superior plants. They showed me the undesirable plant types first with viners and bushers and we all agreed these had to go. Then they showed me the in between rows with some favorable plants but enough fruit or plant flaws that it was understood they would be tilled under as well after a couple more commercial harvests. Then I witnessed the 5 best rows; each exhibited market quality fruit on open, bush plants, fruits borne at a good angle, and some even had very few spines on the petioles (leaf stems.) These rows had at least 70% good plants and the ~30% less favorable plants weren’t overly bad. Upon further inspection one of the 5 rows was not up to the standard. The decision was made to till the other 22 rows in the field and only allow the best 4 to intermate for the next generation of selected seed.
In summary, the 22 non-selected rows were tilled under. Of the remaining 4 selected rows, about 30% of the poorest plants were pulled and destroyed. Lastly all the fruit from the remaining plants in the four selected rows was harvested no matter the size so there would be no chance of a pollination event from the plants that had been eliminated. The best plants in the four rows were then allowed to intermate openly and set fruit. This method furthered the breeding progress by allowing for evaluation of the previous generation and intermating of the best offspring for the next generation in a single season. The intermated seed was harvested from the 4 rows separately into 4 bags. The idea was there would still be shared family characteristics within each row despite the out-crossing to the other rows. Indeed, the out-crossing was by design to reinvigorate each full-sib family with some genetic variation from the other elite rows after the selfing event of the previous generation. With this out-crossing between progeny rows these 4 families became half-sib families as the pollen source was unknown.
In 2005 the seed from these 4 half-sib family rows was planted in two large blocks along with the original ‘Black Eel; and ‘Raven’. Each variety had 4 rows in each of two locations or replications [“reps”] in the field. Bill and Donna harvested this field as a crop while scrutinizing it for all of the agronomic and fruit traits heretofore mentioned. While all 4 families had a high percentage of superior plants and superior fruit only one of the 4 families really started to emerge as a consistently excellent type through the scrutiny of multiple commercial harvests. The half-sib family that traced back to hand pollination #41 (of the original 50+ attempted) was truly superior with an excellent plant type with virtually no bushers, a good angle for the fruit set, and a low degree of petiole spines. It also has a great fruit type that is dark green, cylindrical, and has a good length to diameter ratio for a uniform harvest. It was decided that this family was the only one worth advancing and so the other 3 families plus the comparison rows of ‘Black Eel’ and ‘Raven’ were tilled up with only the two blocks of #41 remaining in the field. These rows of #41 were scrutinized thoroughly. Any plants within this half-sib family with flaws was pulled and destroyed. Very few flawed plants were found. All remaining plants were allowed to intermate to produce seed of the prototype variety ‘Dark Star’ to be tested in 2006.
