In Miniature

My unnamed micro-tomato variety.

I've been growing miniature-sized tomato plants for several years. They first got my attention because I could grow them in a balcony-railing planter right outside my kitchen. Soon after I decided I wanted to breed new varieties that could grow in the same tiny spaces. A few years in, I'm stabilizing one new micro-tomato variety that produces larger fruit than any of the varieties I started with. (Later on in the growing season, I'll be able to illustrate the size difference in the fruit.)

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Breeding a plant to be shorter can allow it to direct more of its resources into producing the fruit or seeds we're interested in rather than the stems we find less useful. This reallocation comes at the cost of the plant being overgrown by weeds much easier, so the plants require our assistance to do well.

Efforts in the 1930s-1960s to breed wheat, barley, rice, and maize into shorter, more productive versions is part of what we now refer to as the Green Revolution. Though changes in crop production systems and agricultural inputs also were also developed during this period, the alteration of plant structure through breeding efforts is considered to have been a major factor responsible for increasing grain production during that time period.

There are efforts to produce dwarfed tomato varieties for field production, such as the Ground-Dew and Ground-Jewel varieties from the University of Minnesota. These are a size up from the micro varieties I've been working with.
Right now I have eleven plants of my micro-tomato variety growing in a two square foot planter. A single normal sized plant will occupy a much larger space. It will be interesting to compare the production of my micro plants vs. an individual normal sized plant in my garden by the end of the growing season.

Even if the micros can produce more mass of tomatoes for a given area than a normal sized variety, it doesn't necessarily mean such a small variety would be useful for field-scale production. In a small planter, I can keep ahead of weeds to a degree that would be cost-prohibitive in a field situation.

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Until recently, I hadn't thought about growing miniature versions of other crops. A few days ago I learned of a corn variety called, "Mini-Maize". It, like the first micro-tomatoes was bred for use as a research plant. The smaller size and shorter life-cycle allows more plants and more generations to be grown in the limited spaces available in a research biology lab. A plant biology researcher I interact with occasionally on Twitter has offered to send me some seeds for this corn, so maybe I'll be adding this crop to my balcony garden.

Unknown dwarfed sunflower mutant.

A few years ago I found this photo of a mutant sunflower that came out of some research program. I haven't been able to find any detailed description of it, nor can I currently find where the photo came from. Like the other dwarfed crops I've mentioned, I can imagine this plant might be more efficient at seed production with respect to area. I can also imagine how any weed pressure at all might negate those gains. I'd really love to have seeds from such a plant, as I can easily imagine growing them on a windowsill.

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What is it that makes a plant dwarfed? The classical story is of hormone production or response. Gibberellins are one group of plant hormones that , among other roles, are responsible for stem elongation. If a plant produces lower levels of these gibberellins, or the receptors that allow cells to respond to them, then the plant will have shorter stems than usual.

This can potentially happen without reducing the size of other plant parts, resulting in short plants with normal sized leaves and fruit. This ideal reallocation of energy resources in the plant to our goals doesn't always happen. In the real world, the fruit or seed cluster size is often reduced somewhat along with the overall size reduction because of a link between gibberellins and meristem size. A smaller floral meristem results in a smaller flower and then fruit. Recent research suggests stem elongation and fruit size are regulated by gibberellins via different pathways, so we may be able to resolve the issue in the future and thus further increase crop productivity.


References:

• Mini-Maize: http://www.genetics.org/content/early/2016/07/15/genetics.116.191726
• Tomatoes:
• Micro-Tom: https://www.totallytomato.com/P/00468/Micro+Tom+Tomato
• List of ten micro-tomato varieties: https://www.renaissancefarms.org/seeds/10-varieties-of-miniature-dwarf-tomatoes-under-8-inches-tall/
• Ground-Dew and Ground-Jewel: https://mnhardy.umn.edu/varieties/vegetables/tomatoes
• Dwarf Millet: http://www.caes.uga.edu/newswire/story.html?storyid=4701&story=Dwarf-millet-discovery
• Green revolution:
• https://geneticliteracyproject.org/2017/08/25/selective-breeding-shorter-plant-stems-contributed-green-revolution-yield-gains/
• https://www.learner.org/courses/envsci/unit/text.php?unit=7&secNum=4
• https://hubpages.com/education/The-Green-Revolution
• Biology of dwarfed plants:
• http://lifeofplant.blogspot.com/2011/03/hormones.html 
• Atkinson et al. "Ears, Shoots, and Leaves." Nat Plants. 2017 Sep;3(9):686-687. doi: 10.1038/s41477-017-0010-z (Pubmed link.) (Sci-hub link.)