IZU, Japan — For three decades, Mitsuyasu Asada has proudly maintained the same lush mountainside terraces where his father and grandfather grew wasabi, the horseradish-like plant with a fluorescent green hue and sharp pungency that unmistakably symbolizes Japanese cuisine.
But at just 56, Mr. Asada is already thinking about retirement, exhausted by the many threats facing this indispensable condiment who graces plates of sushi and bowls of soba.
Rising temperatures make his crops more susceptible to mold and rot. He worries about unpredictable rainfall, flooding and more intense typhoons. The dense cedar forest that covers the mountain overlooking its rice paddies – a result of post-war timber policies – has compromised the quality of the spring water the wasabi needs to grow. Wild boars and deer increasingly attack his fields, which are driven down the mountains at higher elevations due to lack of nutrition.
And his two grown daughters are married and have shown no interest in succeeding him on his five acres in Izu, a town in Shizuoka Prefecture, about 90 miles (145 kilometers) southwest of Tokyo.
“If no one takes over,” Mr. Asada said, “it will end.”
Mr. Asada is just one of several growers in Shizuoka, one of Japan’s largest wasabi-growing regions, facing the mounting challenges of global warming, the legacy of unmanaged forests and demographic decline.
These dangers have already put an end to the ancient culture of wasabi in the area and have jeopardized the future of one of the prefecture’s main agricultural products and a mainstay of its tourist activity.
According to the Ministry of Agriculture, Forestry and Fisheries, the volume of wasabi produced in Shizuoka has decreased by nearly 55 percent over the past decade.
“I have a sense of crisis,” said Hiroyuki Mochizuki, president of Tamaruya, a 147-year-old company in Shizuoka that processes wasabi for sale in tubes, as well as salad dressings, flavored salts, pickles and even nostril-ticking chocolate.
“To protect Japanese food culture,” he added, “it is important to protect wasabi.”
The wasabi that comes in tubes and packets that many guests know is actually a mix of wasabi and horseradish dyed green – or contains no wasabi at all. In Japan, chefs at higher end sushi, soba or grilled beef restaurants grate fresh wasabi onto the counter so that customers can experience the acute attack on their nostrils and the unique taste that lingers on the tongue for just a moment.
For hundreds of years, wasabi grew wild in the mountains throughout Japan, thriving near forests and huddled along streams. About four centuries ago, growers in Shizuoka started growing wasabi as a crop.
Wasabi plants germinate in spring water that flows down from the mountains, helping to promote degrees of tartness and hints of sweetness. The most famous Shizuoka variety, called mazuma, tends to sell 50 percent more than wasabi from other parts of Japan.
According to local growers, the quality of the spring water has deteriorated over time due to an abundance of cedar and cypress trees.
In an effort to provide Japan with a burgeoning source of timber to rebuild after World War II, government planners seeded mountain regions exclusively with Japanese cedar or cypress.
But when cheap timber imports supplanted Japanese timber in the 1960s, the cedar and cypress continued to grow, displacing other types of plants that better contain and nourish the mountain resources that wasabi needs to thrive.
“People are talking about climate change and how there is less water,” said David Hulme, a retired Australian journalist who now grows wasabi in Okutama, about 50 miles (80 km) from central Tokyo. “But the real problem is that the hills don’t hold the water long enough.”
Global warming has further disrupted the balance. The delicate wasabi plants, which take more than a year to mature, do best in conditions no higher than about 70 degrees Fahrenheit. In recent years, heat waves in Japan have regularly pushed temperatures into the 90s and even above 100 degrees, causing more stems to rot.
On a recent afternoon, Masahide Watanabe, 66, a fourth-generation grower, stepped into one of his rice paddies in blue waders. With a small hoe, he dug up a wasabi plant from the mud and discovered a pockmarked green rhizome that sprouted leaves in the shape of water lilies.
He rinsed the plant in running spring water and chopped off the leaves and a tangle of roots, inspecting the remaining body for stains.
“Sometimes the plant lacks the stems growing out of the top,” he said. “We call it ‘headless syndrome’.” Other times, he said, he discovers what look like tumors on the roots. Such illnesses, he said, have become more common as temperatures have warmed.
Government researchers and local growers have begun experimenting with hybrids in an effort to develop sturdy wasabi varieties that will thrive even in the rising heat.
The challenge is that, unlike other crops such as cucumbers or tomatoes, extracting seeds and growing seedlings from wasabi requires advanced technology. Most growers rely on specialized companies to clone seedlings in labs and greenhouses. Crossing new varieties involves complicated pollination efforts, and most importantly, time.
“It could take five, six, or even ten years to figure out the whole process and figure out what’s best or strongest,” said Susumu Hisamatsu, director of the wasabi production technology division at the Shizuoka Research Institute of Agriculture and Forestry. .
Even if the hundreds of experiments by government researchers produce a variety that can withstand the heat better, there’s no guarantee it will taste good or sell well.
Kichie Shioya, 65, whose family farm dates back to the 1800s and who heads the Federation of Wasabi Cooperatives in Shizuoka Prefecture, said that when he tried one of the new hybrids developed by the prefectural research center, the plants ” did not grow well, or got diseases.”
Some experts who study wasabi say modern growers have already narrowed the ability to develop eco-friendly plants because they’ve focused on a small cluster of varieties for so long.
“Now one variety of wasabi dominates the market,” said Kyoko Yamane, an expert in wasabi cultivation at Gifu University. That makes it difficult to produce healthy hybrids.
Growers may not stay in the business long enough to try the new hybrids. As farmers approach retirement age, some are left without successors to continue the wasabi growing tradition.
Mr. Watanabe, the fourth generation grower, reluctantly returned to Izu from Tokyo 40 years ago after graduating with a degree in chemistry. He said his son, who is currently enrolled at a university in Tokyo, will likely look for a job in the city.
“There is a risk that wasabi could disappear,” said Mr. Watanabe.
Hope may yet come from the likes of Haruhiko Sugiyama, 44, who recently started his own wasabi cultivation operation in Izu. He leases half a hectare of rice from a retired grower whose own son does not want to join the family business.
Ten years ago, Mr. Sugiyama, the son of supermarket owners, decided he wanted to work outdoors. A high school friend descended from a long line of wasabi farmers introduced him to another farmer who needed help.
But to get to the point where he could start his own business, Mr. Sugiyama proves his worth to the local growers’ association, which controls access to wasabi fields. In the 12 years he worked for another grower, Mr. Sugiyama, he never took a day off learning every step of the local wasabi growing techniques.
“In a sense, it’s a closed society, made up of people who have been growing wasabi for generations,” said Sugiyama, who was eventually allowed to take over abandoned rice paddies. “If I were not recognized by the association, they would not help me or grow me on favorable land.”
As a sign of the bond he has built with fellow growers, his high school friend and another farmer recently helped cut down a 9-meter-tall cypress tree that had blocked sunlight from reaching some of Mr. Sugiyama’s rice fields. .
As the growers winched the fallen tree onto the bank of a stream that opened into Mr. Sugiyama’s rice paddies, he gazed down at two empty terraces, the clear waters of which now reflect the blue sky above. “Next month,” he said, “I’ll plant them.”