Photos courtesy of Lara Brindisi

As popular as basil is with consumers, and given its economic importance to our industry, this culinary herb has yet to benefit from the intensive research treatment enjoyed by crops such as corn, wheat and soy.

It’s also no secret that the pipeline of new degreed or experienced talent simply isn’t flowing as freely as it did in years past. Recruiting new talent who have either the credentials or experience you need for your growing operation is only getting tougher.

So, I decided to hit two birds with one stone in this month’s column and introduce you to my ASHS Mentee, Lara Brindisi, a Ph.D. student at Rutgers University, and share one of our conversations. She is a basil breeder studying how to make basil that can better adapt to climate change, diseases and other abiotic and biotic stresses.

I’ve been working with Brindisi as a mentor to develop her professional goals as she works to finish her Ph.D. I’ve also gotten to learn a bit more about her fascinating basil research along the way.

Leslie Halleck (LH): Before we get into your background and the nitty gritty of your research, what applications from your research do you feel would be useful to growing basil under glass or in controlled environments?

Lara Brindisi (LB): My lab works directly with growers, both outdoor and indoor, to improve basil. New Jersey has a large acreage of outdoor basil production, but also several indoor controlled environment, vertical farming and glasshouse production systems. Personally, my work with the indoor growers in and outside of New Jersey has been on observing the changes in plant chemistry and nutrition and working with the Tepper lab to observe the changes in human sensory perception in response to altering the environment.

LH: Wait, human sensory perception?

LB: It’s very useful to understand how the environment changes aromas, flavors and the underlying chemistry of plants, because then growers can change the lighting or fertilizer regime, for instance, to drive basil to produce a more powerful and/or desirable aroma and increase their market potential.

LH: OK, that’s cool … What new or interesting developments are you seeing emerge from your basil research?

LB: We have made a ton of progress in a relatively short period of time. We recently sequenced a reference genome, for instance, and this will help us and other labs learn so much more about the genetics, which we can apply directly to improving basil varieties. I am also working on CRISPR/Cas9 editing for basil, which is an exciting technique to learn as it has an immense amount of potential for helping crops adapt to climate and disease.

LH: What’s new and exciting on the horizon for food producers/basil growers you want to make sure readers know about?

LB: The Simon lab is working on improving downy mildew resistance in basil without losing key aroma and visual attributes. Keep an eye out for improved DMR (Downey Mildew Resistant) sweet Italian basils and new Thai basil and lemon basil.

LH: Oh, that’s exciting, as downy mildew is such a significant problem for the industry these days. There are already several cultivars that have been released through your program (readers can find those here: bit.ly/BasilRutgers). I know you are also working on chilling tolerance in basil, which could increase its field production range, as well as potentially reduce input costs under glass. I’m a bit of a basil junkie myself. What is your favorite basil to grow and why?

LB: I’m growing at least two varieties at any given time. I grow ‘Rutgers Obsession-DMR’ for Italian- and American-style dishes. It’s my favorite of the Rutgers downy mildew resistant varieties with a floral sweet basil aroma. Sometimes I also grow a traditional Genovese variety for these dishes, but it doesn’t always make it if it gets downy mildew. For Asian-style dishes, I grow Thai basil like ‘Queenette’. We’re currently working on improving Thai basils for downy mildew resistance as well.

LH: Great to hear. So, what got you interested in the research program at Rutgers and what specifically attracted you to the research on basil?

LB: I initially joined the Ph.D. program in Plant Biology at Rutgers University because the Simon lab offered a unique opportunity to intersect all my deeply seeded passions (pun intended) including sustainable agriculture, medicinal chemistry and international development. I spent the first few years of my program working on the chemistry and nutrition of African indigenous vegetables and vertically farmed baby leafy greens. However, in that time, I learned so much more about the field of genetics through my teaching assignment and my courses that I decided to transition my work towards plant breeding and genomics and our basil breeding program offered a much better opportunity to learn those skills. Plus, I can’t deny the Italian heritage that loves sprinkling basil in every meal.

LH: I could talk basil with you all day, but we only have so much space and time to do so. To wrap up, are there any thoughts about your work or the impact you hope to make?

LB: Plant breeding has been a historically male-dominated discipline, but we are seeing a flux of women enter the field (myself included). I’m excited to see how my contemporaries and I transform the space over the next 10, 20, 30 years, especially because our work is becoming more and more important with growing threats to global food production. Most of the food chain is in the hands of women. Empowering women to be in positions to make decisions on how to adapt is crucial to finding solutions to these challenges

Agreed, it’s wonderful to see so many women, such as Brindisi, entering the field. And it’s been educational and inspiring for me to collaborate with her — she’s going to make a meaningful impact wherever she lands, be it industry or academia.

If you want to get a behind-the-scenes peak at Brindisi’s work, follow her on Instagram at @larabrindisi.

Let’s be real here: It’s going to feel freakin’ fantastic to wave goodbye to 2021 in a few weeks.

Travel restrictions, beloved local businesses faltering en masse, horticultural supply chain collapses precisely when you needed that sleeve of plastic 10” pots the most — it’s been a dredge and a slog and whatever other word you can toss around to describe such a depressing stretch of time.

That being said, I like to mostly keep it positive here (and in life), so let’s go ahead and state the obvious: it feels like the worst of it is now mostly in the rear-view.

Society is opening back up — the U.S. is now allowing (vaccinated and COVID-free) international visitors, a boon for our very much globally-connected horticulture industry — and people are getting comfortable doing business again the way we did it back when Corona was merely the brand name of a skunky-tasting, mass-produced Mexican lager.

I’ve just returned from a quick visit to local mega-greenhouse Green Circle Growers in Oberlin, Ohio, which is just under an hour away from our headquarters in the Cleveland metropolitan area. It was refreshing and exciting and mentally stimulating just to do what used to be so very routine — getting out of the office, away from the endless emails and Zoom meetings, and learning from the talented growers and impressive operations that make this industry so special.

Conventions and grower workshops and greenhouse tours are all returning in full force over the next year, and I’d encourage you (if you’re comfortable with it, of course) to get back out there and get some of that sweet, sweet travel #inspo back into your life. You never know where or from whom that next big idea that will transform your business will come from.

So, from our team to yours, Happy Holidays, and a very merry New Year to all!

Photo: ©Vectormine |adobestock

Produce Grower: What is Unfold and what do you do?

John Purcell: When I was heading R&D for Bayer vegetables, we were looking at the vertical farming space and thinking, what can we do to provide some products and solutions for that sector? We recognized that the best way to do that was to launch a separate company — Unfold. Bayer and a large firm out of Singapore, Temasek, provided $30 million to start Unfold with this idea that we’ll be 100% focused on providing seeds for the vertical agriculture sector. So that’s what Unfold is. We’ve been around for about a year now. We’re building our own R&D facility in Davis, California. We’ve also started trialing at a Bayer site near there and with external customers as well.

PG: What’s different about being a seed provider for vertical farms versus typical outdoor farms?

JP: When you’re breeding lettuce, for example, for open field production, a lot of your time is spent trying to provide a robust disease resistance package. So, one advantage of vertical farming is you’re indoors, so you dramatically reduce pest pressure. The other thing is when you’re breeding for outdoors, the weather conditions can change dramatically. So, you also have to build in a certain amount of reliability for that crop to thrive under diverse environmental conditions. But in indoor agriculture, you’re controlling that environment, so you don’t have to worry so much about if the plant will be successful under all these different conditions, which allows you to focus your breeding on quality traits at the consumer level.

PG: Where do you see the vertical farming industry going in the future?

JP: Most of the investments in vertical so far have been on the operational side. But now you’re seeing companies like Unfold trying to provide the raw materials and seeds that make vertical farms successful. So that’s one evolution that’s happening. Another is the portfolio of crops. Vertical farms are heavily focused on leafy greens like spinach and lettuce, and also microgreens, herbs and spices. But to reach its full potential, the industry has to make the leap to fruit crops. There are a couple of vertical farms looking at tomatoes, berries, peppers and cucumbers, and that’s a big shift. You have to grow the whole salad, not just the leafy greens.

This interview has been edited for length and clarity.

Figure 1. Six different LED lighting treatments delivered in a growth chamber.  Photos courtesy of Qingwu Meng and Erik Runkle.

The last two articles in this series discussed the role of broad-spectrum light-emitting diodes (LEDs) in indoor (vertical farming) lettuce production. This article centers around far-red light and its effects on indoor baby lettuce growth under different light intensities, or photosynthetic photon flux densities (PPFDs).

Far-red light is barely visible to the human eye but has great influence on how plants grow. Plants have light sensors, or photoreceptors, that are sensitive to far-red light. Phytochromes are the photoreceptors that plants use to detect red and far-red light. Direct sunlight has similar amounts of blue, green, red, and far-red light, with a red-to-far-red ratio of 1.2. Leaves absorb most red light but transmit or reflect most far-red light. As a result, the red-to-far-red ratio is as low as 0.2 under the canopy. This is a shade signal that makes plants develop longer stems and larger leaves to intercept more light. Taking this concept from nature, indoor growers may use far-red light to increase light capture, whole-plant photosynthesis, and harvestable yield.

The PPFD describes how many photosynthetic photons fall in one square meter every second (µmol·m^–2·s^–1). Traditionally, the PPFD is defined for photons at wavelengths between 400 and 700 nm, including blue (400 to 500 nm), green (500 to 600 nm), and red (600 to 700 nm) light. Although the traditional PPFD definition excludes far-red light (700 to 750 or 800 nm), recent research has shown that far-red light also promotes photosynthesis and thus could be included in an extended PPFD definition. In this article, we use the traditional PPFD definition (400 to 700 nm) and discuss how adding far-red light to red + blue light influences the growth of two baby-leaf lettuce cultivars.

Experiment protocol

We sowed seeds of green-butterhead lettuce ‘Rex’ and red-oakleaf lettuce ‘Rouxai’ in 128-cell inserts cut into 12-cell sections and filled with a peat-perlite substrate. All of the seeds germinated under transparent humidity domes in a growth chamber at 68 °F under continuous cool-white fluorescent light. Three days after seeding, we transferred seedlings to each of six adjustable LED modules in another walk-in growth chamber (Figure 1). We configured the modules to six different lighting treatments with three far-red photon flux densities (0, 30, and 75 µmol·m^–2·s^–1) under each of two PPFDs (180 and 360 µmol·m–2·s–1; 50% blue + 50% red). We used a high percentage of blue light (50%) because our previous research showed that the effects of far-red light on lettuce seedlings were weaker under lower blue light.

We grew the plants at 72 °F under continuous light. The photosynthetic daily light integrals (400 to 700 nm) under the two PPFDs were 15.6 and 31.1 mol·m^–2·d^–1. A recommended daily light integral for head lettuce production is typically no more than 17 mol·m^–2·d^–1 to avoid tipburn, which is a symptom of calcium deficiency that is exacerbated by high light. Baby-leaf lettuce is less susceptible to tipburn, so we attempted to maximize yield by applying high light to promote photosynthesis and growth. The high plant density in baby greens production minimizes light waste in non-plant areas and the lighting cost per plant. Therefore, the high light output is more justifiable for baby-leaf lettuce than head lettuce.

During the experiment, we sub-irrigated the plants daily with a nutrient solution made from a 13-5-13 fertilizer. We collected growth data 8 and 13 days after seeding for lettuce ‘Rex’ or 10 and 17 days after seeding for lettuce ‘Rouxai.’

Results

Green-leaf lettuce ‘Rex’

Growth trends were similar for plants harvested 8 and 13 days after seeding (Figure 2). Under the PPFD of 180 µmol·m^–2·s^–1, adding 30 or 75 µmol·m^–2·s^–1 of far-red light increased shoot fresh weight by 34% to 42%. However, far-red light did not affect shoot fresh weight under the PPFD of 360 µmol·m^–2·s^–1. Therefore, for lettuce ‘Rex,’ 30 µmol·m^–2·s^–1 of far-red light was worth adding under the lower PPFD, which is typical in vertical farms, but not under the higher PPFD.

Without far-red light, doubling the PPFD from 180 to 360 µmol·m^–2·s^–1 increased shoot fresh weight by 42% to 54%. With far-red light, however, doubling the PPFD did not affect shoot fresh weight. Therefore, considering both energy consumption for lighting and crop yield, the PPFD of 180 µmol·m^–2·s^–1 with 30 µmol·m^–2·s^–1 of far-red light was the best of our lighting treatments for lettuce ‘Rex.’

Increasing the intensity of far-red light increased leaf length under the PPFD of 180 µmol·m^–2·s^–1 and, to a lesser extent, under the PPFD of 360 µmol·m^–2·s^–1. However, the increase in leaf expansion was not always accompanied by a yield increase. Therefore, combining a high PPFD and high far-red light was not worthwhile for lettuce ‘Rex.’

Red-leaf lettuce ‘Rouxai’

Plants responded to the lighting treatments somewhat differently 10 and 17 days after seeding (Figure 3). On day 10, under the PPFD of 180 µmol·m^–2·s^–1, adding 30 µmol·m–2·s^–1 of far-red light increased the total photon number by 17% but increased shoot fresh weight by 46%, at least partly because far-red light increased leaf length by 26% for more light capture. Increasing far-red light further to 75 µmol·m^–2·s^–1 did not affect shoot fresh weight, although it increased leaf length. On day 17, increasing far-red light from 0 to 75 µmol·m^–2·s^–1 increased shoot fresh weight and leaf length linearly. The effects of far-red light on yield were generally similar under the two PPFDs.

On day 10 and 17, doubling the PPFD from 180 to 360 µmol·m^–2·s^–1 did not affect yield of lettuce ‘Rouxai’ in most cases. We only observed a 22% yield increase by doubling the PPFD in the absence of far-red light on day 17. Therefore, the yield of lettuce ‘Rouxai’ was efficiently maximized under the treatment with a PPFD of 180 µmol·m^–2·s^–1 and 75 µmol·m^–2·s^–1 of far-red light.

For red-leaf lettuce, yield was only part of the story; leaf color was also an important trait. A high percentage of blue light, such as 50% that we used, can intensify the red color relative to a low percentage of blue light. However, as shown here, 50% blue light produced lighter and less saturated and uniform redness under the lower PPFD than under the higher PPFD. The deep, rich, and consistent red pigmentation under the higher PPFD was similar to what can be obtained under direct sunlight. Since different degrees of leaf redness may be acceptable depending on the market, whether the higher PPFD is necessary is situational.

Take-home messages

Adding far-red light to red + blue light increased baby-leaf lettuce yield in some cases. The effects of far-red light depended on the lettuce cultivar, PPFD (red + blue light), and plant age. The yield of green-leaf lettuce ‘Rex’ was the highest under the PPFD of 180 µmol·m^–2·s^–1 with 30 µmol·m^–2·s^–1 of far-red light. The final yield of red-leaf lettuce ‘Rouxai’ was the highest with the addition of 75 µmol·m^–2·s^–1 of far-red light. Interestingly, doubling the PPFD had no statistical effects on lettuce growth when far-red light was added, but the higher PPFD intensified the red-leaf coloration of lettuce ‘Rouxai.’

Dr. Qingwu (William) Meng (qwmeng@udel.edu) is an assistant professor of controlled-environment horticulture in the Department of Plant and Soil Sciences at the University of Delaware. Dr. Erik Runkle (runkleer@msu.edu) is a professor of horticulture in the Department of Horticulture at Michigan State University (MSU).

Acknowledgments: We thank Osram Opto Semiconductors, MSU’s Project GREEEN, the USDA Specialty Crops Research Initiative, and horticulture companies that support vertical farming research at MSU.