It's the winter avocado harvest at the University of California's orchard in Lindcove, and the fruit jumbled in the back of Eric Focht’s SUV are a palette of earthy tones, some rough and flecked with frosted tips, others green and smooth. The horticulturist selects three miniature fruit, bright green and rotund, which together fit easily in the palm of his hand. “We were thinking of calling it the Lunch Box,” says Mary Lu Arpaia, who oversees the avocado breeding program at the orchard. But for now it’s just an experimental variety, officially known by a string of numbers. It’s too soon to tell if “Lunch Box” will ever be released to the world.

Chances are you haven’t eaten—or perhaps even heard of—an avocado other than the Hass, which makes up 95 percent of the US market. Beloved in guac or trendy on toast, Americans ate 2 billion pounds of them last year, more than quadrupling consumption 15 years ago. But for California avocado growers, that astounding growth is limited by climate and geography. Twenty years ago, a thin coastal corridor in Ventura and San Diego counties met nearly all of the country’s demand for the finicky, water-intensive fruit. Now the region supplies around 10 percent, overtaken by a flood of imports from Mexico and South America as California’s spigots run dry and planted acreage wanes.

The California avocado industry grew on the back of its star variety, and consumers continue to demand more. But Arpaia envisions a time when the avocado will be more like an apple, with unique varieties harvested in different seasons and across an expanded geography—perhaps even here in the stifling heat of the San Joaquin Valley, hundreds of miles north from the coastal epicenter of US production. “If we want to stay on the game as California avocado growers, we need to bring diversity back,” she says. For 70 years, the university’s breeding program has worked in close partnership with the avocado industry, which pays for the care of Lindcove’s experimental trees. But today, in these boom times for the Hass, it’s unclear if the industry is willing to gamble on anything else.

Ripe for Tonight

The Hass avocado (which rhymes with “pass,” by the way) was an accidental discovery—a seedling of unknown parentage planted in 1926 by its namesake, postman Rudolf Hass. Farmers heralded the productive and compact tree, and shoppers loved the buttery, nutty fruit. But it wasn’t perfect. “Its single disadvantage is its black color which has been associated in the minds of the public with poor quality fruits,” said a report in the 1945 yearbook of the California Avocado Society. Avocados of the time came in many shapes, sizes, and colors—and the most popular variety, called Fuerte, ripened green.

Shoppers, already skeptical of this exotic, big-seeded snack of Pleistocene megafauna, couldn’t discern unripe from rotten. So in the 1970s, the avocado industry looked to the banana for inspiration, which had perfected the art of pre-ripening fruit for the shopper. Hass fruit has the benefit of hanging for months on the tree—a kind of natural storage—and once off the tree, a carefully controlled supply chain can see the fruit darken just as it reaches grocery shelves. Black skin, to quote a 1980s marketing campaign by the California Avocado Commission, told wary shoppers that a Hass was “ripe for tonight.”

Once demand for the fruit exceeded the output of the brief California harvest season, the US opened its market to Mexican avocados—but only to the Hass, which had been individually cleared as hosts of invasive pests. Since the mid-1990s, imports have dominated the market, enabling packers to streamline year-round supply chain carefully tuned to the Hass’s preferred temperature and humidity. In years when California’s drought-stricken farms fail to produce—as the Avocado Commission expects next year, when yields are expected to plummet by half—they can easily fill the difference. “They give you something that’s very predictable,” Arpaia says.

Just as predictable, however, are the downsides of a Hass monocrop. The explosive growth of Hass acreage represents a petri dish for pests. “In history the worst case of famine and epidemics are because of monoculture” says Patricia Manosalva, a plant pathologist and biochemist at the University of California-Riverside. She points to laurel wilt, a disease spread by an invasive beetle that has felled vast stands of redbay trees, which share the Persea genus with avocados. The disease has gradually spread west from Georgia to Texas—not far from Mexico, the avocado’s ancestral homeland, and a natural germplasm of native relatives. “We may be looking at a nuclear bomb for the industry."

The Experimental Orchard

Lindcove sits on the eastern edge of the San Joaquin Valley, where California’s vast expanse of farmland abruptly rises into the chalky yellow foothills of the Sierra Nevada. A northern outpost of the University of California-Riverside, the avocado breeding program here is funded by the California Avocado Commission. Tonight, the first freeze warning of the season is in effect, and workers test out a wind turbine that will blow a gentle breeze over the vulnerable trees. As we walk through the orchard, Arpaia pauses by an early victim—a drooping tree with leaves browned by cold air rushing downhill.

“The industry wasn’t really too keen about me putting a site here,” she says with a shrug. “But I’m stubborn and that’s why it’s here.” Summer in the San Joaquin Valley is even more dangerous. At around 90 degrees, the stomates on Hass leaves begin to close—any warmer and they’ll begin dropping their flowers and fruit. Temperatures at Lindcove regularly climb beyond 100 degrees.

The area could be well-suited to avocados in other ways, Arpaia contends: Despite the drought, water remains cheaper here and salinity—a bane of avocado roots—is less acute than in Southern California, where farmers increasingly rely on recycled water. Each year the program plants three new varieties here and at three other locations in the heart of avocado territory, keeping careful watch for outliers that perform well at extreme temperatures. “We can look at the role of environment and what it does to fruit development,” she says. In addition to experimental varieties—commercial growers call them “telephone number” varieties—the orchards also include heirlooms, like Fuerte.

Arpaia has also planted the industry standard Hass, both to see how to improve its tolerance and as a control. “It’s a very high standard,” Arpaia says. Only a few varieties have surpassed it, and none have caught on commercially. The current prodigal scion is Gem, which was patented and released six years ago. It’s more compact and less water-intensive than the Hass, says Rob Brokaw, who sells seedlings at Brokaw Nursery in Ventura County. “A few years ago, I would have said a new variety no matter what its virtues would have had no chance,” he says. But now he hopes to get ahead of the industry by teaming up with like-minded farmers and a packer to market the fruit through specialty retailers.

Unseating the Avocado King

The experimental program’s slow progress is largely due to the painstaking process of classical breeding. For avocados, hand pollination is impossible—a single tree can produce more than a million blossoms, but just a few hundred will ever bear fruit. “So you just have to leave it open to whatever is going to come in,” says Focht. Although the breeders try to keep track of the potential dads whose pollen blows through, that’s also tricky because the avocado flower can act as male or female depending on the time of day.

But the real trouble lies in the avocado’s murky genetics. Avocados are remarkably heterozygous, meaning that selection by phenotype can yield surprises—good ones, like the unplanned wunderkind Hass, but mostly frustrations. “You can pick two parents that have a small tree architecture and hope that you’ll get small tree architecture out of it,” says Focht. “But then you get big trees and little trees out of it.” So once seeds are achieved, the team raises hundreds of seedlings—of which about 1 to 2 percent of which are worth keeping—to see what shape they’ll take and what fruit they’ll bear. The entire process, from pollination to patent, typically takes at least 17 years.

The breeding process, in many ways, is out of a different time. “We’re probably 20 years behind the apple industry at this point,” says Arpaia, which underwent its own transition from Red Delicious domination to the dozen or so varieties seen in grocery stores today. A complete avocado genome was only just sequenced in Mexico, and is not yet publicly available. Marker-assisted breeding—mapping phenotypic traits to specific molecular markers in the avocado DNA—is seen as the way to speed up selection, explains Manosalva. But she cautions that selection for complex, polygenic traits related to avocado fruit production likely remains far away.

In the meantime, progress is slow and expensive—prohibitively so, if you ask the program’s funders in the avocado industry. In 70 years of searching for new varieties, the breeding program had failed to produce a new variety that could best the Hass. So in 2014 the industry cut funding to a bare minimum—enough to keep the orchard’s vital germplasm going, but not to plant new varieties. Tim Spann, research program director at the California Avocado Commission, says the industry is concerned about long-term diversity and pests like laurel wilt. But there are more immediate worries for farmers, like the Hass’s tolerance to salinity and common pests like root rot. “We decided we can’t fund everything,” Spann says.

Arpaia acknowledges the program needs to evolve—there’s talk of sequencing the genome at the university and making it public. But she also plans to begin planting more trees at Lindcove this spring with traditional breeding, using a funding source from outside of the industry. And while she has high hopes for the nascent Gem variety, she still holds out hope for something that could truly thrive in the heat of the San Joaquin Valley. “That’s the dream,” she says, gazing across her wayward northern orchard. “Do we have anything out here that’s going to achieve that dream? I’m not so sure.”