Vertical Farms Bear Fruit
Cathryn A. O’Sullivan, C. Lynne McIntyre, Ian B. Dry,
Susan M. Hani, Zvi Hochman & Graham D. Bonnett
Nature Biotechnology volume 38, pages160–162(2020) Cite this article
Engineering perishable crops for use in indoor farms promises to expand the adoption of this high-yielding, efficient means of food production.
Climate-controlled farms, including vertical indoor farms and greenhouses, have the potential to improve food security for the growing number of city dwellers worldwide. However, only leafy greens and herbs are grown commercially in most indoor farms1. If indoor farming is to realize its potential to increase fruit and vegetable production globally, the diversity of crops that can be grown indoors must increase. In this issue, Kwon et al.2 showcases the application of genetic technologies to modify both plant architecture and flowering times in tomatoes and groundcherries. This is an important example of how to expand the diversity of crops that can be grown in vertical farms.
Urban farming includes conventional soil-based outdoor smallholder farms, rooftop farms, greenhouses, and indoor, light-emitting diode (LED)-lit vertical farms. Urban agriculture accounts for 5–10% of global production of legumes, tubers, and vegetables, and is, therefore, an important source of income for producers and of food for their consumers3. Urban farms occupy less land than traditional farms, partly because of the higher cost of urban land compared with rural land. Recently, investment in sophisticated climate-controlled farms has increased. The most advanced of these are indoor, vertical, soil-less systems that have hydroponics or aeroponics culture setups with temperature and humidity controls, LED grow lights, automated nutrient dosing, pH controls, and CO2 enrichment.
Urban farms (indoor, greenhouses, or netted areas) in which the growing conditions are controlled can achieve substantially higher yields per unit area (kg/m2) than field farms while consuming orders of magnitude less water4. Stacking plants vertically indoors further increases the yield per unit area. Climate control can enable year-round harvests of high-quality, locally grown produce out of season. Crops grown indoors are not exposed to extremes of heat or cold, frosts, hail, drought, or flood. Fully enclosed farms physically exclude pests and diseases, resulting in a reduction in the use of fungicides and pesticides. Finally, growing perishable crops closer to consumers can shorten supply chains, reduce transportation and the associated economic and environmental costs of food miles, decrease storage times and provide consumers with products that have a longer shelf life.
Leafy crops currently grown in vertical indoor farms are small in stature, have short times to harvest, have a high harvest index (all the aboveground biomass is harvested, unlike with fruits) and relatively low photosynthetic energy demand, and grow well in soil-less systems. These crops are also high in value per unit weight, which is a requirement for high-tech farms to be economically viable. Yet the value of leafy crops for food security is debatable. Most fruit and vegetable crops (including tubers and legumes) are not well suited to indoor, climate-controlled farms, and developing appropriate varieties will require optimization of several traits (Fig. 1). Indoor fruit crops need short life cycles, continuous flowering, low root-to-shoot ratio, increased performance under low photosynthetic energy input, and desirable consumer traits, including taste, color, texture, and specific nutrient contents.
In previous work, researchers have changed the architecture of grapevine by exploiting a naturally occurring mutation5 and of kiwifruit by applying gene editing6. In the present study, Kwon et al.2 engineered dwarf tomato and ground cherry plants by targeting a newly identified internode locus (SlER) and stacking this trait with mutations for compact growth habit and rapid flowering (SP5G) and for precocious flowering (SP). By editing three genes and using CRISPR–Cas9 for forward and reverse genetics, they rapidly altered a plant phenotype for indoor production.
The edited tomato varieties are well suited to indoor farming systems. Kwon et al.2 confirmed that the plants expressed the target traits of small stature, early yield, and rapid cycling both in traditional, soil-based field trials and in a commercial vertical farm under LED lights. They also found that, although the tomatoes produced were slightly smaller than for the wild type, each plant produced more fruit, and they had a similar sugar content (an important quality indicator) to the wild-type variety.
In this2 and previous5,6 reports on engineering dwarf crops, the plants exhibit continuous and/or precocious flowering, which greatly increases productivity and enables year-round production. Notably, different sets of genes were modified in tomato and groundcherry, grapevines, and kiwifruit to create the dwarf varieties. So, engineering indoor-farm-friendly plants of other species, such as pepper or cucumber, for example, may require different genetic changes. Even if there are several potential ways to engineer or breed dwarf, continuously flowering plants, the set of genes identified and targeted by researchers so far2,5,6 is likely to prove a useful starting point in a range of species.
For indoor farming to be broadly adopted, the capital and operating costs of climate-controlled farms must be reduced, or they will benefit only the wealthiest communities. These technologically advanced systems are capital intensive and out of the reach of most growers. The energy costs of crops grown in indoor farms far surpass those of field-grown crops7. The development of cheaper, more efficient LEDs was a crucial advance8, but other factors, such as linkage to renewable energy and waste heat reuse, are needed to further improve system economics. Urban farms are well placed to reduce waste by closing loops for water and nutrients, as well as energy, but more innovation is needed to make the recycling of urban waste into growing systems safe, efficient, and economical.
Agronomic research is required to assess how much climate control is needed to optimize crop management. In Australia, for example, greenhouses in peri-urban zones may be more appropriate than indoor farms in urban areas, because the climate is warm, with plenty of sunlight, and restrictions on available land are not extreme. In developing countries, research is needed to assess what capacity there is for smallholders in urban and peri-urban areas to benefit from intensifying production systems and what level of technology is appropriate. Advanced indoor farms are not likely to be feasible for many smallholders because of the associated costs, but there may be ways to use adapted crops in lower-tech, lower-cost systems, such as shaded structures with hydroponics, to increase yields and mitigate weather-related problems.
Although it is unlikely that indoor farms will provide all our staple dry goods (such as wheat and rice), they could increase the production of perishable fruits and vegetables, such as tomatoes, berries, capsicums, and spices. These horticultural products are a crucial source of vitamins, minerals, and fiber. Any plant that has high value and is eaten fresh could be grown indoors, but in many cases will be commercially viable only if genetic innovations such as those reported in Kwon et al.2 can be more broadly applied.
Fruits and vegetables that grow on bushes or vines (tomato, strawberry, raspberry, blueberry, cucumber, capsicum, grapes, kiwifruit) are likely to be most readily adapted for indoor farms, but high-value specialist crops (hops, vanilla, saffron, coffee) and medicinal or cosmetic crops (seaweed, echinacea) might be next.
One day, it is conceivable that even small trees (chocolate, mango, almonds) may be grown indoors. Importantly, the adaptation of a wide variety of plants for indoor cultivation could ensure that these crops can still be harvested in a future with an uncertain climate. Other products, such as medicinal cannabis, and insects and algae, which are used as alternative protein sources, are already being produced in indoor farms9.
Urban agriculture has existed for centuries, but the climate-controlled urban farming industry remains in its infancy. Interdisciplinary research in genetics, plant biology and physiology, agronomics, farming systems, engineering, and physics will be needed to improve the cost-effectiveness and productivity of modern urban farms. Broad-acre farmers and consumers have benefited from knowledge provided by agricultural researchers over centuries. Urban agriculture must receive similar support if it is to help feed growing urban populations in the face of increasing climate variability.
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CSIRO Agriculture and Food, Queensland Biosciences Precinct, St. Lucia, Queensland, Australia
Cathryn A. O’Sullivan, C. Lynne McIntyre, Ian B. Dry, Susan M. Hani, Zvi Hochman & Graham D. Bonnett
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Correspondence to Cathryn A. O’Sullivan.
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O’Sullivan, C.A., McIntyre, C.L., Dry, I.B. et al. Vertical farms bear fruit. Nat Biotechnol 38, 160–162 (2020). https://doi.org/10.1038/s41587-019-0400-z
Published14 January 2020
Issue DateFebruary 2020
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