Sex and the Single Asparagus

When planting new asparagus fields, the advantages of choosing the newest Rutgers hybrid male varieties far outweigh the disadvantage of increased cost. We asked Steve Garrison, Rutgers Professor Emeritus, to discuss the benefits of these new, expensive varieties that will be increasingly offered by seed companies worldwide since Rutgers NJAES recently both licensed and sold its asparagus-breeding program. Finally, we test your memory of high school biology describing how 45 years of genetics and technologies research made hybrid all-male asparagus production fields possible.

Rutgers Hybrid Male Asparagus Variety Benefits

Asparagus spears emerging in a field of Rutgers NJAES all-male hybrid asparagus

Rutgers Hybrid Male Asparagus

According to Dr. Garrison, the best Rutgers hybrid males out-yield females by 15-25% over time – the differences increasingly apparent after the 2nd and 3rd years. One reason for this is that the male plants do not produce fruits (seeds) which would divert crop energy resources away from future stalk growth. Hybrid male asparagus emerge earlier in spring under colder soil conditions than females. In addition, hybrid male production fields are longer-lived. Compared with females, the hybrid male stalks fetch better prices due to a higher percentage of yield pack out of desirable USDA No.1 Grade diameters of medium and large. In asparagus, the larger diameter spears have superior culinary qualities of tenderness and sweetness.

Hybrid males have beneficial characteristics in the field: because they don’t produce seed, they don’t produce inferior volunteers that demand cultivation and herbicide weed management; and, unlike mature female plants weighed down by seed, hybrid males are less likely to lodge in rainy, windy conditions.

The Rutgers parent lines became a series of superior male hybrids recognized worldwide, with much sought after consistency. For these reasons, the more expensive Rutgers hybrid male varieties pay their way.

Hybrid Male Asparagus “Old School” Genetics and Tissue Culture Technology

If you had a penchant for wandering through asparagus fields you may have happened across Rutgers asparagus breeder Professor Howard Ellison on one of his many field explorations, as I did some three decades ago. Ellison had a keen eye and while scouting in the 1960s found a few vigorous surviving crowns among diseased plants on the Riggins family farm in Greenwich, NJ that displayed tolerance to Fusarium rot. On other scouting explorations, he found hermaphrodite asparagus – male plants with female organs. With physiological coaxing, these asparagus plants were successfully self-pollinated. What did this mean for asparagus breeding, you ask? It’s a long story that begins with a reflection back to your high school biology days.

A majority of crops are monoecious, for example pumpkin and corn, and have separate male and female flowers on the same plant. Other monoecious crops, such as tomato and soybean, have male and female reproductive parts within the same flowers (so-called “perfect” or bisexual flowers). Less common are dioecious crops, that have male and female flowers on separate plants. Asparagus is a dioecious plant, as is Cannabis. Humans too, most typically exist as separate male and female individuals.

While human and asparagus genetics of sex expression are not identical, determining sex expression ratios in offspring can be similarly understood. We can refer to the asparagus sex determination gene as xY. If a seed is homozygous xx, the plant is female. If it is heterozygous xY, the plant is male. Presence of one Y allele determines maleness, so maleness is dominant. We can predict the sex ratio of the offspring by using the Mendelian principal of segregation for simple inheritance, and construct a Punnett square table:

Male Parent
x Y
Female Parent x xx xY
x xx xY
Out of a large asparagus population, half (50%) the offspring are likely to be xx female and half (50%) are likely to be xY male.

The male hermaphrodite asparagus plants discovered by Dr. Ellison produced unique results when self-pollinated:

Male Hermaphrodite
x Y
Male
Hermaphrodite
x xx xY
Y xY YY
In a large population of self-pollinated hermaphrodite asparagus, we get a ratio of approximately one-quarter (25%) female offspring, and three-quarters (75%) male offspring. From the males that were YY, Ellison bred “Rutgers Supermales” parents.

The RU Supermale parent is crossed with a female parent with the following results:

RU Supermale
Y Y
Female Parent x xY xY
x xY xY
The seed generated from the RU Supermale and female parent line crosses result in 100% male F-1 Hybrid plants in the field. These hybrid male asparagus plants possess the beneficial characteristics discussed by Steve Garrison.

 
A problem remained: asparagus suffers from severe inbreeding depression (reduced biological fitness) which made the task of creating sufficient quality and quantity of seed impossible. Over the course of many decades, Rutgers Professor Chee-kok Chin discovered a method to clone asparagus plant tissue in culture. This discovery allowed sufficient quantities of pure supermale and female parent lines to become available for hybrid seed production.

Innovation Comes with a Price Tag

Rutgers hybrid male asparagus varieties are a culinary prize for consumers and an important commercial production advancement for farmers.

Asparagus-Garrison-Kinelski

Researchers Steve Garrison and John Kinelski
evaluate asparagus.

We depend on such innovation to solve agricultural problems. However, innovation is not possible without financial support to train skilled individuals, create and maintain research farms, and foster collaboration between scientists and farmers – a relationship facilitated by Cooperative Extension.

This particular innovation resulted from dedicated efforts by at least three ag scientists, spanning two generations over more than 45 years aided by technicians working in fields and labs. Other keen observers found male hermaphrodites as well, but it was the expertise of Rutgers investigators who knew more than anyone else in the world about the creative use of supermales that delivered the goods. Facilities also play their part, for none of this would have been possible without the use of two adequately funded, expertly staffed Rutgers Ag Experiment Station farms.

We live in a society that rails against private lab-based genetic modification of crops. That same society continues along the path of reducing funding for traditional public university field-based crop breeding. What’s the outcome when you say no to GMO’s and no to public breeding programs? You’re out of luck if your plan is to solve either local or global food problems through innovation.

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