Test-tube Berries
The Recorder. March 7 2015. Story by Tom Relihan & Photos by Micky Bedell
Emptying a bowl full of fresh strawberries, raspberries and blackberries into the blender, slopping in a spoonful of vanilla yogurt and jabbing the “mix” button with your finger to make that morning smoothie, there’s no way, you may find yourself thinking, that the fruit you’re using came from a local farm this time of year.
And that’s probably mostly true. Mostly, but not entirely.
Though the sweet and sour berries now traveling up your straw may first have traveled to Franklin County from as far away as California, there’s a slight chance that the plants they were plucked from got their start locally, in the greenhouses of Whately’s Nourse Farms.
Tim Nourse, along with his wife, Mary, and son, Nate, have owned and operated the berry farm on River Road since 1968, when they purchased it from a friend and relocated it to Whately from Andover. Prior to that, Nourse, who grew up on a dairy farm, was working as a chemical and fertilizer salesman but knew he wanted to own his own farm.
“Growing up on a dairy farm, I knew I didn’t want to milk cows for a living, so it was an opportunity to grow crops and something that was of interest,” he said, of the purchase.
For the past three and a half decades, the farm has been producing dormant, bare-root berry plants through a plant propagation method known as tissue culture, the process of growing full plants from plant tissues on a sterile nutrient medium in a controlled environment — no soil needed.
According to Dr. Mark Bridgen, a professor of horticulture at Cornell University and the coauthor of a book about the method, “Plants From Test Tubes,” tissue culture was originally developed by orchid breeders in the 1950s to improve the odds that their seeds would produce full plants — orchids do not have endosperms, one of the key parts of germination, so only a few of the thousands of seeds each plant produces will sprout in nature. By manufacturing the optimal conditions for growth, it almost guaranteed each seed would produce a viable plant. By the early 1970s, he said, the method had caught on commercially.
Nourse was an early adopter of the process, which allowed him to exercise a greater amount of control and precision in how his plants were produced and ensure a disease-free stock.
“In 1980, I went to a conference where they talked about making plants from bits and pieces, and for me, it was the introduction to tissue culture,” Nourse said. “We presumed this could be an important step for us to take to increase our quality and competitiveness, with all the science to do it better.”
By the end of that year, Nourse had opened the farm’s first tissue culture lab as a pilot program to see how it worked out, and, when it showed promise, expanded it in 1982. After practicing tissue culture for nearly 30 years, Nourse built a new, larger lab in 2010 to keep up with increased production.
Designing out disease
That lab, a large red building off the north side of the farm’s main office, incorporated a disease analysis and diagnostic lab on site, which allowed the farm to identify viruses in its stock plants at a very early stage — often before they even begin to show symptoms or characteristics — through a variety of modern diagnostic methods. It’s the first, and one of the most important, steps in the Nourse’s production process, he said.
Prior to the installation of the lab, Nourse said the farm used simple screen cages to cover the plants and prevent disease-carrying insects, such as aphids, from getting to and infecting the plants.
“There’s a whole list of viruses that can affect the plants,” he said. “Aphids are insects that we have all around us all the time, but they’re vectors, and when they bite the plants, they spread the virus.”
By switching to tissue culture, Nourse gained the ability to intercept the viruses between the time the plant was infected and before propagation began.
The first test the lab uses analyzes the plant’s DNA through a diagnostic method known as polymerase chain reaction, or PCR. The test, Nourse said, involves running the sap from the plant’s leaves through an electrical field to separate the proteins and provide a photographic “fingerprint” of the DNA, along with any viruses that have infected the plant. The picture is then compared to a reference picture of known viruses to check if any are present.
“A virus like tomato-ring spot virus, for instance, has a specific fingerprint, and if that shows up in the test results, then that indicates a positive for the virus,” he said.
The second diagnostic method the lab uses is known as enzyme-linked immunosorbent assay, commonly referred to by its acronym, ELISA.
Nourse said that process provides results in about two days — much faster than the leaf-grafting method the farm used prior to opening the lab, which could take several weeks. According to the Mayo Clinic, the same process is commonly employed within the medical industry to identify substances or pathogens in blood and urine, like HIV, Lyme disease and the Ebola virus, and also to test for allergies or the presence of drugs.
“It’s very accurate, and gives a very early detection in just a couple days,” Nourse said.
After the viruses are identified, measures are undertaken to eradicate them, including baking the plants in a special heat treatment unit. The process usually kills the plant as well, but as long as enough healthy material remains, the tissue can still be harvested for propagation, Nourse said. The lab also has its own ventilation and heating systems to contain the viruses and make sure they don’t spread to the facility’s production area.
“That’s a very important part, making sure the materials in the system remain clean,” said Nourse.
Having the capability to easily spot and destroy viruses within the plant material before cloning new plants from the clean meristematic tissue — groups of plant cells harvested from plants that have the ability to divide and form new tissue — gives the farm the advantage of being able to ensure that all the plants the farm produces are grown from the best, healthiest source.
“The primary motivation for tissue culture with strawberries and raspberries is that, with all the diseases they have — particularly the viruses — there’s a process of growing those plants and taking meristematic tissue that ensures that we can produce the highest quality material,” Nourse said.
To ensure that the test results taken at the lab are reliable and accurate, the farm participates in a certification program under the state Department of Agriculture, which sets test standards and monitors the results by taking samples of the plants from the farm’s fields. In order for the plants to be shipped across the country or around the world, Nourse said, they must receive a phyto-sanitary certificate through the program.
To further ensure accurate testing, the farm also sends samples of all of its stock plants to a third-party lab every three years.
Liquid soil
Once the plant material is free of contamination, the propagation process can begin in earnest. At the beginning of each growing season, enough stock plants are removed from the greenhouse to supply the farm with enough material to produce the plants it will need two years in the future.
Carefully, the meristematic tissues — often no bigger than a single millimeter — are removed from the plants under a dissecting microscope and placed into autoclave-sanitized containers or test tubes with a layer of gelatinous growth medium on the bottom.
The medium, mixed daily on a stirring plate in the lab, is based on a substance called agar, which consists of a mix of sugar, all of the nutrients that are needed for the plants to begin growing without being planted in any kind of soil, and growth regulators, to ensure the plants grow correctly.
“It’s got all the components of soil in a liquid solution,” Nourse said.
For some plants, charcoal is also added to the mix, acting as a natural filter to prevent unwanted chemicals from building up in the medium.
Sealed and secured with plastic wrap to avoid further contamination, the containers are placed on metal racks and bathed in fluorescent light in the lab’s growing room, where the tissue inside establishes itself and begins dividing into tiny plantlets.
When the plantlets have grown into clusters, each is separated by lab technicians, fingers working deftly with tweezer and scalpel under special laminar hoods, which use flowing air to keep contaminants out.
After they’ve been separated, the plantlets are placed on new media formulated to help them further divide and proliferate. This stage makes up the bulk of the process and is performed over and over until the desired number of plants are produced.
“That part is about 80 percent of what the lab is doing,” Nourse said.
The third phase involves changing the growth regulators in the media to prepare the plants to be planted in soil and moved into the farm’s greenhouses. During the fourth phase, the plants are finally plucked from their containers and the media is washed off of their roots before they’re placed into tiny cubes of soil.
A sea of green
Once inside the greenhouses, the plants are kept in conditions designed to promote each stage of growth. Each of the greenhouses are separated from each other and the atmosphere in each, including the temperature, humidity, and watering schedule, is independently controlled through sensors and computer systems. The system even uses retractable screens on the ceiling to provide shade for the plants during the peak of the summer or insulation in the dead of winter.
Take a quick walk between the long greenhouses and the difference is apparent: stepping out of the cold and through the door of the first greenhouse, glasses and camera lenses fog up almost instantly, blocking from view the sea of green produced by hundreds of plant-filled plastic trays on racks running the length of each unit.
Pass into the next greenhouse and vision clears just as quickly as it was obscured: this unit is kept much cooler, closer to the temperature of the air outside, and is used to harden the plants so they’ll survive being stored in 28-degree temperatures before being shipped.
As the sun sets, a series of purple lamps on the ceiling flick on, casting a violet glow on the fledgling berry bushes.
To further prevent bugs and diseases from getting to the plants, the greenhouses are equipped with devices that trigger when the door is opened and prevent outside air from flowing in, similar to the laminar hoods.
“Some of the bugs transmit the viruses and that keeps them from infecting the plants,” said Nourse. “These are state-of-the-art stock houses, they’re required for the certification.”
An unusual operation
According to Bridgen, farms practicing tissue culture in the way Nourse does are relatively uncommon in New England. Most of the country’s largest tissue culture labs and micropropagation facilities are located in the south, mostly in Texas or Florida, and concentrate on producing ferns or other foliage, not berry plants.
In the industry at large, tissue culture isn’t particularly common in the United States, he said, with most propagation routinely outsourced to overseas facilities because of their lower labor costs.
Today, Nourse’s berry plants are purchased by farms all over North America, including some in California, Colorado, Mexico and Canada. “Raspberries will grow in almost any state in the country, and we ship to most of them,” Nourse said.
He travels constantly to monitor trials of new varieties to see how they perform and set up sales. He said people who purchase Dole brand berries can expect that some of them were probably picked from plants that got their start at Nourse.
And if they’d like their fruit picked closer to home, some of the plants are planted in its fields throughout the growing season so people can get strawberries, blueberries and raspberries though the farm’s pick-your-own operation which is priced by weight.
Nourse said his farm is one of only about five in the country that are using the process to produce fruit and berry plants. Today, it employs between 70 and 100 people, depending on the season. The farm also produces rhubarb and asparagus, though not through tissue culture.
“I think we were one of the first entities in the U.S. doing tissue culture in strawberries and raspberries,” he said. “The whole concept and the propagation of the plants has probably allowed us to stay in business and maintain our competitiveness and growing quality.”
On the Web: http://noursefarms.com/
