Research update

Conventionally bred papaya
still possible, even in California

UC researchers believe there may be a market for papayas grown in California as an annual crop.

Commercial papaya production worldwide has
been hurt by the plants' high susceptibility to papaya ringspot virus (PRSV), a disease transmitted by aphids that has swept through the tropics, beginning in India and Puerto Rico in the 1940s, moving to the main Hawaiian growing area in the 1970s, and Australia in the 1990s.
In the mid-1990s, scientists took a single gene from the virus itself and inserted it into the papaya's genetic code. That tiny change prevents the virus from making copies of itself and stops the disease from damaging fruit and killing the plants. Papayas are often held up as a classic success story for agricultural biotechnology (page 92). However, planting genetically engineered papayas is not the only way to skirt PRSV.
Last year, six UC Cooperative Extension farm advisors traveled to the Mexican state of Veracruz to gain a better understanding of Mexican production techniques, insect- and disease-control methods, and import-export issues in the tropical region. They found farmers using an unconventional papaya-production practice to successfully grow fruit that has not been genetically engineered.
At Rancho Neveria, a small farm near the city of Cardel, papaya is grown as an annual crop rather than a perennial tree, to manage the virus. Agronomist Honorio Fernández described the ranch's annual papaya-production system, from the soil mix for seedlings to plant spacing in the field. The plants are started in a screen house (an enclosure to screen out insects) to protect them from disease-transmitting aphids. About 1,225 seedlings are transplanted per acre in the field, he said. Before harvest, a quarter of the plants are pulled due to viral infection. Nevertheless, the approximately 900 remaining plants produce a profitable crop before succumbing to disease.

At a Mexican farm, Honorio Fernández explains how papaya is grown as an annual crop in order to manage the papaya ringspot virus. Thousands of seedlings are started in a screen house, above, and the survivors are transplanted to the field.

Although California lies well outside the papaya's favored climate zone between the Tropics of Cancer and Capricorn this approach to papaya production could be profitable for the state's small-scale farmers.
UC Cooperative Extension farm advisor Manuel Jimenez is studying papaya production at the UC Kearney Research and Extension Center near Parlier. A typical San Joaquin Valley winter will kill the unprotected plant, squeezing the growing season between February and November. That time frame only allows the fruit to reach unripe maturity, but unripe papayas are suitable for cooking and popular with consumers of Asian descent. The unripe fruit may be baked like winter squash or pumpkin, or used for chutney. A group of marketers who visited KREC last year thought the locally grown fruit was good quality for the "green" market.
"We had Hmong, Burmese, Mexican, Japanese and Laotian papaya marketers prepare green papaya salads," Jimenez says. "They all prepared the papayas differently, but they were all delicious."
Jimenez grew several varieties of nongenetically engineered seed, and lost nearly all of the cultivars from Hawaii to PRSV. He said the Chinese plants showed more natural resistance. He was only able to harvest the green papayas for 3 weeks, not long enough for a fruit marketer to abandon the tropical papaya provider.
"Papaya is very inexpensive to grow," Jimenez says. "We can plant an acre for $20 of seed, compared to several hundred dollars an acre for traditional vegetables. Papayas may be a crop for growers who direct-market their produce."
In fall 2004, Jimenez will try to protect the plants from cold weather under movable "hoop houses." If they survive the winter, the papaya fruit on those plants might ripen the following season, giving potential growers greater harvest flexibility and, perhaps, making papayas commercially viable for California small-scale farmers.

— Jeannette Warnert Back to top

UC researchers evaluating
genetically engineered alfalfa

When the herbicide glyphosate is sprayed over the top of Roundup Ready alfalfa, it kills the weeds and a very small percentage of plants that do not possess the glyphosate-resistance gene. Photo: Steve Orloff.

UC Cooperative Extension farm (UCCE) advisors and researchers are growing genetically engineered (GE) alfalfa in small experimental plots to determine whether the technology will be beneficial to California farmers.
"We would like to be ready with research-based answers when this technology is introduced," says Steve Orloff, Siskiyou County farm advisor. "It's somewhat controversial, but providing unbiased research results will enable growers to make intelligent decisions about it for themselves."
Although final results are not yet in, the UC scientists believe that the new varieties, which have been genetically engineered for resistance to the herbicide glyphosate (Roundup), could be an important new tool for alfalfa growers.
"It won't be a silver bullet for all farmers," says Kurt Hembree, Fresno County weed science advisor. "Glyphosate is weak on some important alfalfa weeds, like malva, nettle, hairy fleabane and filaree. Successful weed control with this technology will depend a great deal on the ability of the growers and pest control advisers to accurately identify their specific weed problems before treating."

The untreated control (right) is clearly weedy; a plot treated with conventional herbicides (left) is better but there is crop injury; and the glyphosate-resistant alfalfa (back) is the least weedy with no observable crop injury. UC Cooperative Extension farm advisor Steve Orloff and student assistant Josh McCollam (on tractor, top) inspect alfalfa at the Intermountain Research and Extension Center.

Alfalfa is grown on more acres in California than any other crop and is the third most valuable crop in the United States. But because it is used primarily for dairy feed and is a few steps removed from the dinner plate, the general public does not often recognize its importance." Alfalfa is ice cream in the making," quips UC Davis alfalfa specialist Dan Putnam.
In anticipation of a possible 2005 commercial release of gyphosate-resistant (Roundup Ready) alfalfa, UCCE farm advisors and specialists are evaluating it in the Intermountain Region and throughout the Central Valley. "We rate the trials blind," Orloff says. "We don't favor one approach over others."
Weed control a challenge
Weed control is a major challenge for alfalfa growers. Alfalfa contaminated with too many weeds may be unpalatable to livestock and less nutritious. In California, lower-quality alfalfa hay is worth an average of about $44 per ton less than premium hay. With the Roundup Ready alfalfa plant, growers can spray glyphosate over the crop after the alfalfa and weeds have emerged, eliminating nearly all the weeds. Later herbicide sprays may be unnecessary as the alfalfa grows vigorously and shades later-emerging weeds.
Reducing pesticide use in alfalfa could provide environmental benefits. "Alfalfa growers are working closely with state agencies to prevent runoff of insecticides and herbicides into streams and rivers," says Mick Canevari, San Joaquin County farm advisor. "This new technology may reduce the amount of pesticides that are needed to grow the crop, and thereby reduce the risk of pesticide runoff with some of our winter-applied herbicides."
However, concerns remain. Canevari has seen a "weed shift" in his experimental plots in Stockton, where glyphosate-resistant alfalfa has been grown for 3 years. "When we started this study, there were four or five stinging nettle plants on this end of the field," Canevari says. "Now you can see nettle all along the field. We're seeing more and more nettle each year."
Another worry is the development of herbicide-resistant weeds. Certain weeds such as ryegrass over the years have developed resistance to glyphosate. "At this point, we already have glyphosate-resistant corn and cotton. Alfalfa is being studied and I have a project with Roundup Ready wheat. If you were to rotate between these crops, I wouldn't recommend growing Roundup Ready crops successively," says Ron Vargas, Madera County farm advisor. "That's really setting yourself up for weed resistance."
Financial viability unknown
The economic feasibility of growing glyphosate-resistant alfalfa has not yet been studied because Monsanto has not announced the pricing formula for the alfalfa seed. Unlike most other Roundup Ready crops, alfalfa is perennial and does not need to be reseeded each year. An annual lease on the glyphosate-resistant trait or a price premium for the seed that takes into consideration multiple years are being considered. The UC field trials should assist growers in making an economic evaluation of the technology, since comparative yields, application rates and weed-control efficacy are being studied.
UC researchers are also considering the potential market acceptance, since growers will want to know whether buyers will purchase GE alfalfa hay. Putnam says he does not expect much resistance from the dairy industry, since it has already absorbed a number of similar technologies. Most cheese, he points out, is currently made from rennin from
GE microorganisms. However, he says, there might be some consumer resistance to the GE alfalfa in markets that import California hay, such as Japan.
"In my discussions with exporters, there will likely be initial resistance from the export market, since some Japanese consumers are reluctant to purchase genetically engineered foods. That will likely moderate over time and will be price dependent," Putnam says. "Organic producers will reject the technology, as they do all herbicides. Some horse owners may also initially balk at the use of genetically engineered alfalfa, but they may also quickly realize the benefits, since a number of horses die each year from poisonous weeds that could be easily removed through this technology."
For more information, go to: http://alfalfa.ucdavis.edu.

— Jeannette Warnert Back to top

Pollen movement studied
UC scientists are studying the movement of honeybees that are commonly used to pollinate alfalfa seed fields in California. Seed production methods in alfalfa are receiving renewed attention with the likely introduction of Monsanto's glyphosate-resistant (Roundup Ready) trait in alfalfa.

Photo by Larry R. Teuber

Alfalfa varietal purity is affected by unintended gene flow, the movement of genes that can occur when a bee carries a pollen grain from a distant source, pollinates a flower and a seed is formed. A field study that measured alfalfa gene flow was conducted during 2003 by UC Davis professor Larry R. Teuber, alfalfa geneticist in the Department of Agronomy and Range Science; Shannon Mueller, Fresno County farm advisor; and Allen Van Deynze of the UC Davis Seed Biotechnology Center. The researchers used the experimental Roundup Ready trait as a pollen-marking tool to maximize the sensitivity of the gene flow detection method and they isolated the test plot from other alfalfa by 6 miles.
The pollen source plot (6 acres) was tenfold larger than each of the pollen trap plots (0.55 acres each). First-year results indicate that under these conditions, at 900 feet (foundation class isolation) the amount of honeybee-mediated gene flow was about 1.5%. This amount was five times greater than that previously reported at 900 feet, when leafcutter bees were used as pollinators. For seed growers wishing to minimize the adventitious (unintended) presence of off-type genes, modifications to current pollination or isolation practices may be needed.
"These studies are confirming what we have suspected, but until now we did not have the research tools available to conduct such a precise study," Teuber says.            — Editors