- Author: Emily C. Dooley, UC Davis College of Agricultural and Environmental Sciences
Strawberries selectively bred for Fusarium wilt resistance and high yields
The University of California, Davis, is releasing five new strawberry varieties that are resistant to the soilborne disease Fusarium wilt, have high yields and improved fruit quality.
UC Eclipse, UC Golden Gate, UC Keystone, UC Monarch and UC Surfline will be available for sale to California nurseries from Foundation Plant Services in April.
Roughly 88% of strawberries grown in the nation come from California. Fusarium wilt is one of the most common reasons for crop loss and death and yet 55 to 59% of cultivars planted in the state since 2014 have not been resistant, according to UC Davis research.
This is the first release from the UC Davis Strawberry Breeding Program where all the cultivars have Fusarium wilt resistance. They are meant to replace susceptible plants on the market such as Monterey, UCD Royal Royce and UCD Valiant.
Monarch was also developed specifically as a prototype for mechanical harvesting – another first out of the breeding program, which dates to the 1930s and has released 72 patented cultivars over the decades.
“These provide the same yield or better and they are Fusarium resistant,” said Steve Knapp, a Distinguished Professor in the Department of Plant Sciences and director of the UC Davis Strawberry Breeding Program. “They have a better collection of traits. They're superior.”
Knapp is a faculty member based in the College of Agricultural and Environmental Sciences at UC Davis and shares the UC Agriculture and Natural Resources land-grant mission of the Agricultural Experiment Station.
Dangerous pathogen
Fusarium wilt didn't present much of a danger to strawberry crops until after the fumigant methyl bromide was phased out of use in the United States in 2005. But the pathogen had always been in the soil, and cases of wilt appeared a year later and increased over time, leading to concerns that a Fusarium wilt pandemic could destroy the crop in California.
“The disease has taken off fast and we need to react quickly to address the need,” said Glenn Cole, a breeder and field manager with the Strawberry Breeding Program.
Knapp said the program tries to “encourage people to consider things like disease resistance” and routinely invites growers and other experts to events showcasing research breakthroughs and improved cultivars.
Varieties for the seasons
The new strawberry varieties each have improved flavor and characteristics that allow for near year-round growing around California, where about 1.8 billion pounds of the fruit are harvested each year. Some of the cultivars are adapted for production in the southern part of the state while others do well under the long daylight hours of summer along the coast.
Eclipse, a “summer plant” cultivar, has the potential to increase grower profitability as it produces in the fall and winter, and yields during research testing were 54% higher than similar cultivars. “We expect this cultivar to have wide commercial appeal,” Knapp said. “Eclipse is going to eclipse them all.”
Golden Gate and Keystone are “day neutral.” Those type of cultivars grow throughout the summer on about 60 percent of strawberry farming acres in the state. The “short-day” plants Surfline and Monarch are resistant to Verticillium wilt and Phytophthora crown rot.
Surfline and Eclipse are firmer and promise longer shelf lives. Monarch provides growers with improved fruit qualities relative to other mass-producedcultivars and has characteristics needed for advances in mechanical harvesting, Knapp said.
Genetic tools
Breeding program experts have long been researching ways to improve strawberry cultivars so the crop can withstand pests, disease and other stressors. To find plants that had Fusarium wilt resistance, they obtained the DNA of thousands of plants in field studies. The scientists also developed genetic tools to screen the plants and identify the genes that have resistance to the Fusarium pathogen.
Knowing that information allowed the team to breed resistance into and develop new cultivars, at a faster rate than previous efforts. “These tools have allowed us to sweep out the susceptibility and bring in resistance,” Knapp said.
/h2>- Author: Emily C. Dooley, UC Davis College of Agricultural and Environmental Sciences
Resistant varieties to be released later this year to growers
Strawberry losses from Fusarium wilt could become less of a threat after researchers at the University of California, Davis, discovered genes that are resistant to the deadly soilborne disease.
The findings, published in the journal Theoretical and Applied Genetics, are the culmination of several years' work, and the discovery will help protect against disease losses, said Steve Knapp, director of the Strawberry Breeding Program at the college.
“What we've accomplished here is important and it's valuable for the industry and it's going to protect growers,” Knapp said.
Strawberries are a key crop in California, where about 1.8 billion pounds of the nutritious fruit are grown each year, making up roughly 88% of what is harvested in the United States.
Finding the genes could prevent a Fusarium wilt pandemic.
“The disease has started to appear more often up and down the state,” said Glenn Cole, a breeder and field manager with the Strawberry Breeding Program. “Once the wilt gets in, the plant just crashes. You have total die out.”
Searching for resistance
UC Davis scientists screened thousands of strawberry plants in the college nursery and took DNA samples. They then used genetic screening and developed DNA diagnostics to identify genes that are resistant to the primary race of Fusarium wilt.
“The genes have been floating around in the strawberry germplasm for thousands of years,” Cole said, but no one worked to identify them.
This latest development brings “strawberry into the 21st century in terms of solving this problem,” Knapp said.
Protecting future crops
This work means breeders can introduce the resistant gene into future strawberry varieties. This fall the program will release new cultivars that have the Fusarium wilt resistance gene. And the DNA diagnostic tools will help breeders respond to new Fusarium wilt variants that develop.
“There will be new threats and we want to be prepared for them,” Knapp said. “We want to understand how this works in strawberries so that as new threats emerge, we can address them as rapidly as possible.”
“If you don't have fusarium resistance, you're done,” Cole said. “The disease could be around more than you think.”
Fusarium wilt hasn't traditionally been an issue but when the fumigant methyl bromide was phased out in 2005, things changed. The disease was in the soil and without the fumigant, instances of wilt increased, especially in areas where crops weren't rotated.
Breeding new varieties
Knapp and Cole have informed the industry about current strawberry varieties that have the resistance so they can select plants with that added protection. The new resistant varieties coming out later this year will be suitable for several growing seasons.
“It's a big deal,” Cole said. “Everything is incremental in plant breeding, but it's a big deal.”
Plant scientists have been breeding strawberries at UC Davis since the 1930s and they have released more than 60 patented varieties through the public breeding program.
All of the work happened at UC Davis. Dominique Pincot, Mitchell Feldmann, Mishi Vachev, Marta Bjornson, Alan Rodriguez, Randi Famula and Gitta Coaker from the Department of Plant Sciences, and Thomas Gordon from the Department of Plant Pathology contributed to the research, as did Michael Hardigan and Peter Henry who are now at the U.S. Department of Agriculture Agricultural Research Service and Nicholas Cobo who is at University of La Frontera in Chile.
The research was funded by UC Davis and grants from the USDA National Institute of Food and Agriculture Specialty Crop Research Initiative.
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By Susanne von Rosenberg, UC Master Gardener of Napa County
Some gardening advice seems so sensible or obvious, or has been repeated so often, that we “know” it to be true. As gardeners, we need to be careful about falling prey to myths. In this column, we'll explore some widespread gardening myths, although perhaps I should call them confusions.
We are usually told that wilting leaves indicate that a plant needs water. This is often the case, and you can check to see if your soil is dry. But there are other reasons that a plant's leaves could be wilting.
If the soil is waterlogged, the oxygen that roots need to grow is replaced with water. This happens often to plants in containers without drainage. Plants may also become waterlogged in compacted soil that doesn't drain well. When roots lack oxygen, they can't supply water to the rest of the plant. The leaves continue to photosynthesize and to use water. By forcing roots to shut down, waterlogged soil leads to wilted leaves.
Fungal or bacterial disease can also cause leaf wilt. Fusarium and verticillium are common in local soil. These fungi block the plant's water transport structures, causing leaves to wilt even when there is plenty of soil moisture. Often the entire plant dies.
Keeping your soil too moist can promote fungal disease. Another culprit for wilting leaves is animal damage to the roots. Gophers, nematodes and other insects feed directly on roots, and other animals may create tunnels that drastically reduce root contact with surrounding soils.
Another possible cause of wilting is overfertilizing or excess salt in the soil. Always follow the directions on any packaged fertilizer, and be aware that steer manure is relatively high in salt.
You may have heard that bark chips are a better mulch for your perennial woody plants than tree chips. Some say that tree chips could contain disease-causing organisms or compounds that inhibit the growth of other trees.
Neither of these concerns has been documented as a significant issue. Conversely, bark chips, while a more attractive mulch than tree chips, have poor water retention. Tree bark is designed to prevent water loss. It contains a waxy compound, suberin, that repels water.
Tree chips, on the other hand, consist mostly of inner wood, which has the capacity to absorb and hold moisture. Depending on where the logs were stored before the bark was collected and chipped, bark chips can also contain weed seeds. Tree chips are more environmentally friendly, too, because they are local. By using them, you are reducing the amount of material that needs to be processed in a composting facility.
While we're talking about mulch, let's explode the myth that there is any permanent solution for weed control other than paving over your yard. Landscape fabric, which differs from black plastic mulch in having small holes for air and water exchange, is often touted as a permanent solution. It is used in commercial vegetable and ornamental plant production, where it is successful at keeping weeds out. It can also be easily removed and replaced each year.
However, landscape fabric is not good for permanent weed control around perennials. If left exposed, the fabric can degrade in a year. If you cover it with mulch or allow plant debris to accumulate on top of it, weeds will colonize the plant material or mulch and grow through the fabric, making it difficult to remove.
You can cover the fabric with gravel, but you'll still need to keep removing the weeds that manage to colonize gravel-covered fabric. Your plants may also grow into the fabric, so when you remove the fabric, you damage their roots.
As the fabric degrades, you'll have a clean-up and aesthetic headache, with lots of shredded bits. (I know this from personal experience.) Gophers can exert so much pressure building mounds under the fabric that the fabric rips. If it doesn't rip, you end up with exposed landscape-fabric-covered mounds.
Unfortunately, there is no magic bullet for weed control. You can reduce them, but you still need to remain vigilant no matter what method you use. Organic mulches are best as they improve soil texture and health and can be replenished as needed. Couple them with targeted watering.
If you want to learn more about garden myths, Dr. Linda Chalker-Scott, an extension horticulturist and associate professor at Washington State University, has a wonderful website that discusses all sorts of common Horticultural Myths.
Food Growing Forum: Napa CountyMaster Gardeners will present a discussion of “Perennial Vegetables, Garlic and Alliums” on Sunday, October 10, from 3 p.m. to 4 p.m., via Zoom. Register here to receive the Zoom link.
Free Guided Tree Walk: Join Master Gardeners of Napa County for a tree walk in Fuller Park in Napa on Tuesday, October 12, from 10 a.m. to noon. Limited to 12 people per walk. COVID safety protocols will be followed. You will be asked health questions and asked to sign in. Face masks and social distancing are required. Register here.
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to mastergardeners@countyofnapa.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email. For more information visit http://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County.
- Author: Michelle Leinfelder-Miles
In early June 2019, I visited some contiguous garbanzo bean fields in southern San Joaquin County, at the request of the grower. The grower observed that plants were yellowing and dying (Fig. 1) and wondered what might be causing the problem. The grower did not figure that he would be able to do anything about the problem in this year's crop, but he was thinking ahead for future cropping. He doesn't have reliable water at this site, so his cropping options (i.e. rotation options) are limited. He would consider growing garbanzos in these fields again next year unless diagnostics revealed a disease problem.
My observations of the field were that there were patches of several nearby plants with symptoms, but across the three contiguous fields, the patches were widespread. I suspected a vascular disease because of what appeared to be a progression of the disease from yellowing to necrosis to eventually plant death. I submitted samples to the plant pathology lab at UC Davis, and they diagnosed Fusarium oxysporum f. sp. ciceris, which is the Fusarium wilt pathogen for garbanzos. Fusarium wilt (also called Fusarium yellows) has the external symptoms previously described, but in addition to these symptoms, splitting the stems may reveal reddish-brown streaking in the vascular system at the center of the stem (i.e. xylem). The roots won't show discoloration with Fusarium wilt like they will with Fusarium root rot. Fusarium wilt should not be confused with yellowing caused from virus, which will exhibit discoloration in the phloem. Fusarium wilt can reduce yield by reducing seed quantity and size.
In general, cultural practices are the only ways to manage this disease. Luckily, the Fusarium wilt pathogens are crop-specific, so this pathogen will only infect garbanzos. The pathogen, however, can survive for a long time in the soil (upwards of 6 years or more) because it can survive under wide temperature and pH ranges. Therefore, crop rotation is an important management practice. Crop rotation will help to slow the proliferation of the disease, but it generally won't eliminate it. Growers should plant certified disease-free seed. They should not save seed for planting because Fusarium wilt (and Ascochyta blight) can live externally on the seed. Growers should also consider planting UC-27, which has disease resistance and is adapted to the Central Valley. Disease management may also include cleaning soil from equipment when moving from an infected field to a non-infected field. In some studies, soil solarizaton has been shown to reduce Fusarium wilt in subsequent garbanzo crops, but to my knowledge, there hasn't been any work on soil solarization in California garbanzos.
Garbanzo beans are an important crop worldwide for human and animal nutrition. In California, they are grown during the winter months, like small grains, and provide growers with another crop choice that can be winter rain-fed. Because they are a legume, they can fix atmospheric nitrogen to fulfil some of their nitrogen needs. Garbanzos also are more tolerant of soil salinity than common beans and limas. In California, we annually grow approximately 10,000 acres of garbanzos. California garbanzos are generally a high-quality product grown for the canning industry. More information on garbanzo production in California can be found in the UC production manual.
This article was originally posted in the UC Dry Bean Blog.
- Author: Michelle Leinfelder-Miles
My observations of the field were that there were patches of several nearby plants with symptoms, but across the three contiguous fields, the patches were widespread. I suspected a vascular disease because of what appeared to be a progression of the disease from yellowing to necrosis to eventually plant death. I submitted samples to the plant pathology lab at UC Davis, and they diagnosed Fusarium oxysporum f. sp. ciceris, which is the Fusarium wilt pathogen for garbanzos. Fusarium wilt (also called Fusarium yellows) has the external symptoms previously described, but in addition to these symptoms, splitting the stems may reveal reddish-brown streaking in the vascular system at the center of the stem (i.e. xylem). The roots won't show discoloration with Fusarium wilt like they will with Fusarium root rot. Fusarium wilt should not be confused with yellowing caused from virus, which will exhibit discoloration in the phloem. Fusarium wilt can reduce yield by reducing seed quantity and size.
In general, cultural practices are the only ways to manage this disease. Luckily, the Fusarium wilt pathogens are crop-specific, so this pathogen will only infect garbanzos. The pathogen, however, can survive for a long time in the soil (upwards of 6 years or more) because it can survive under wide temperature and pH ranges. Therefore, crop rotation is an important management practice. Crop rotation will help to slow the proliferation of the disease, but it generally won't eliminate it. Growers should plant certified disease-free seed. They should not save seed for planting because Fusarium wilt (and Ascochyta blight) can live externally on the seed. Growers should also consider planting UC-27, which has disease resistance and is adapted to the Central Valley. Disease management may also include cleaning soil from equipment when moving from an infected field to a non-infected field. In some studies, soil solarizaton has been shown to reduce Fusarium wilt in subsequent garbanzo crops, but to my knowledge, there hasn't been any work on soil solarization in California garbanzos.
Garbanzo beans are an important crop worldwide for human and animal nutrition. In California, they are grown during the winter months, like small grains, and provide growers with another crop choice that can be winter rain-fed. Because they are a legume, they can fix atmospheric nitrogen to fulfil some of their nitrogen needs. Garbanzos also are more tolerant of soil salinity than common beans and limas. In California, we annually grow approximately 10,000 acres of garbanzos. California garbanzos are generally a high-quality product grown for the canning industry. More information on garbanzo production in California can be found in the UC production manual.