California Fruit and Vegetable

Tag: University of Florida

  • Results from New Citrus Rootstock, Scion Combination Experimental Grove on HLB Tolerance

    As citrus growers in the west dreadfully anticipate the arrival of the citrus killing disease Huanglongbing, researchers in the already severely impacted state of Florida are making significant strides in learning how to combat this disease.

    Early results from a groundbreaking, large-scale citrus trial looking for solutions to the devastating citrus greening disease have given early hope for growers in the Indian River District. The new UF/IFAS research shows tree size does not seem to affect citrus susceptibility to greening.

    In the trial, researchers are testing which citrus rootstock and scion combinations will tolerate citrus greening, a deadly global citrus disease that nearly decimated the Florida citrus industry.

    Martin Zapien on one of the Millennium Block citrus cultivar trial planting days in 2019.

    Martin Zapien, a graduate student at the University of Florida Institute of Food and Agricultural Sciences Indian River Research and Education Center (UF/IFAS-IRREC), presented data from the Millennium Block citrus cultivar trial in Fort Pierce, Florida. At his thesis defense, the information Zapien represented was research from a 20-acre grove with grapefruit, navel orange and mandarin cultivars on a wide range of newly released and commercial rootstocks. Planted in 2019, the trees grow in a region where citrus greening is now endemic.

    Lorenzo Rossi, UF/IFAS plant root biologist and Tom James, a local citrus industry veteran, supervised Zapien’s research. Advisors on the project were UF/IFAS plant improvement team faculty Fred Gmitter, Jude Grosser and William Castle.

    Nearly 80% of Florida’s grapefruit crop is produced by Indian River District growers, who export their crop to Europe and Asia. That’s why scientists study the fruit so closely, said Rossi.

    “One of our objectives is to evaluate and compare the early performance of several new grapefruit hybrids grown on three commercial rootstocks under citrus greening conditions,” said Zapien.

    In the first two years of growth, the researchers compared UF rootstocks and scions by measuring tree growth and the trees’ ability to tolerate citrus greening. They expect to collect yield and fruit data after the third year, Zapien said.

    Rossi said data sets were specific to tree size, bacteria amount, the severity of citrus greening symptoms such as irregular yellow patches in the leaves, and leaf and soil nutrient concentrations.

    “We have seen many rootstocks that promote large and small tree size, but we have not seen any correlation between tree size and susceptibility to citrus greening,” Zapien said.

    But so far, the research does not support a theory that tree size affects citrus greening susceptibility, but there is a trend in small trees showing less citrus greening symptoms, Zapien said.

    Zapien said published research findings prove that high-density plantings produce higher fruit yields by increasing yield efficiency — fruit number per green foliage. The researchers will evaluate if the trees correlate with the published work or if the larger trees in the test grove produce more fruit.

    ‘Ray Ruby’ grapefruit on UFR-15 rootstock promotes vigorous trees — the trees show the largest canopies and are already flowering. But for UF/IFAS researchers to recommend a particular rootstock and scion combination, more data are required. The experimental grove must be examined for up to four more years before UF/IFAS scientists can make reliable recommendations.

    “All trees in the Millennium Block are infected with citrus greening. However, some trees are thriving,” Zapien said. “Trees on sour orange have shown significantly fewer disease symptoms than trees on x-639 and US-942 rootstocks, but we have to consider that sour orange’s drawback is the susceptibility to citrus tristeza virus.”

    As to citrus greening severity, ‘Star Ruby’ grapefruit showed only 4% symptoms in the green foliage. In contrast, ‘US Seedless Surprise’ symptoms were 24%. The other varieties fall between the two.

    “The data we compiled is nascent as the trees were only two years old at the analysis,” said Zapien. “University researchers will continue to monitor the top performer combinations to determine if the early findings are consistent.”

    With research in the UF/IFAS-IRREC experimental grove, Zapien completed a master’s degree in horticultural sciences. Zapien recommends that researchers improve sampling methods to assess the bacteria as the trees mature to advance the research. Zapien and his colleagues will evaluate flowering patterns to determine when the fruit is ready to harvest and reveals market windows. A long-term goal is to measure the yield or the amount of marketable fruit each tree produces. — By Robin Koestoyo, University of Florida, Institute of Food & Agricultural Sciences

  • A New Way to Battle Powdery Mildew in Strawberry

    Strawberry farmers worldwide may get help from new University of Florida research that shows a way to battle one of the fruit’s fiercest foes.

    The key: combine genomic data with phenomics. The genome amounts to all the DNA in an organism. Phenomics is the study of plant growth, performance and composition. Through phenomics, scientists use DNA to measure plant traits. In a newly published study, UF/IFAS scientists found a new way to help strawberry growers battle powdery mildew.

    Ronald Tapia, a doctoral student at the Gulf Coast Research and Education Center (GCREC), led the research. Tapia worked under the supervision of Seonghee Lee, an assistant professor and Vance Whitaker, an associate professor, both in horticultural sciences.

    Ronald Tapia, a doctoral student in horticultural sciences, points a sensor at a strawberry plant at the UF/IFAS Gulf Coast Research and Education Center. Credit: Courtesy, Ronald Tapia, UF/IFAS.

    Prior research already showed this method detects diseases in other crops, Whitaker said.

    “We already have a lot of technology that helps us understand the genes in strawberries, but those genes still need to be connected to their actual effect on the plant – in this case how the plant resists powdery mildew disease,” said Whitaker. “That’s why we combined genomics and phenomics. Any technology that reduces the cost or increases the speed of evaluating any trait — like disease resistance — in our breeding trials can help us out.”

    Whitaker cautions this method is not guaranteed to work in all situations, but he’s hopeful.

    To reach their findings, Whitaker and his colleagues conducted a field trial of strawberry plants at GCREC. They took DNA from each strawberry and looked at its genes.

    Vance Whitaker, associate professor of horticultural sciences at the UF/IFAS Gulf Coast Research and Education Center. Credit: Tyler Jones, UF/IFAS photography.

    Then they rated the disease using two methods:

    • Their own eyes, which gives them a visual scale. The plants were evaluated the traditional way by eye, recording the severity of the disease, rated on a scale of 0 to 6 for each plant.
    • A handheld sensor. Whitaker and his colleagues used the device to detect wavelengths of light that you can’t see with your eyes. The wavelengths gave researchers data about the health and disease status of strawberry plants.

    “We showed that by combining the DNA information (genomics) and the spectroscopy information (phenomics), we can predict the visual rating of disease resistance surprisingly well,” Whitaker said. “In the future, we can eliminate the work of the visual rating.”

    The finding should help scientists assist strawberry growers globally as they look for powdery mildew in their crop. While Florida produces most of the nation’s domestic winter crop on about 11,000 acres, California produces strawberries nearly year-round. Nationwide, strawberries are valued at about $2.2 billion. — By Brad Buck, University of Florida, Institute of Food & Agricultural Sciences

  • AI Helps Detect Watermelon Disease Quickly, Accurately

    If you savor a juicy watermelon in the scorching summer heat, farmers toil to meet your tastes. But, like all farmers, those who produce watermelons seek ways to control diseases, so they don’t lose all or part of their crops. The needs of growers drive Yiannis Ampatzidis to use artificial intelligence to detect pathogens early and accurately.

    One such disease, downy mildew, spreads like wildfire, said Ampatzidis, an Associate Professor of Ag & Biological Engineering at the University of Florida.

    For a new study, Ampatzidis used AI to help find downy mildew.

    In newly published research, Ampatzidis used spectral reflectance —  the energy a surface reflects at specific wavelengths — of plant canopies and machine learning to quickly and efficiently detect downy mildew in several stages of the disease.

    Hopefully, farmers can take advantage of this technology.

    “If left unchecked, downy mildew can destroy a farmer’s entire crop within days. That’s why it gets the nickname ‘wildfire.’ It spreads rapidly and scorches leaves,” said Ampatzidis, a faculty member at the Southwest Florida Research and Education Center.

    Ampatzidis and his research team successfully detected downy mildew in several stages of severity.

    “Our most important result was finding downy mildew in its earliest stage, which is critical to growers’ ability to manage this disease,” he said.

    Ampatzidis and his research team developed two methods, utilizing hyperspectral imaging and AI — one in the laboratory and the other using UAVs (drones) for field detection.

    Downy mildew does not affect stems or fruit directly. But it can defoliate the plants, leaving fruit exposed to sun damage, making it unmarketable.

    As long as consumers continue to buy watermelon — and those who grow the fruit want to reap a good harvest — Ampatzidis will continue to find ways to find pathogens that could damage the fruit.

    As next steps in his research, Ampatzidis wants to develop a simple and inexpensive drone-based sensor to improve detection of downy mildew in watermelon plants. — By Brad Buck, University of Florida, Institute of Food & Agricultural Sciences

  • Are Finger Limes Just Another Fad?

    There has been growing hype around finger limes from citrus growers, the retail sector, and their customers. Growers are particularly interested in this market as disease pressure such as citrus greening and international competition have made other citrus and fruit markets less appealing. However, many are concerned that finger limes are just a fad and the markets will eventually crash as consumers move on to the next cool food trend. Our research at the University of Florida is examining these markets to determine the potential for growers in Florida and throughout the U.S. to take advantage of the emerging finger lime market.

    Finger limes are known as the “citrus caviar,” because of their unique compressed, round juice vesicles that are distinct from other citrus crops’ delicate, tear shaped fruit sacs. This feature combined with its bright colors and tangy flavor make finger limes a great garnish used in high end restaurants and as a perfect accent to a cocktail. As more and more chefs, bartenders, and suppliers in the hospitality industry become familiar with the fruit, they are falling in love with them and demand for finger limes is rapidly growing.

     Many growers and suppliers of finger limes are hopeful that the demand for this fruit will expand beyond the hospitality sector to mass markets, as consumers across the U.S. and around the world become more familiar with the fruit. Finger limes are not only resistant to greening that plagues orange and other citrus production but also have traditionally been grown using few agrochemical inputs. So, there are expectations that organic markets could provide an additional premium for this fruit. Some research has also pointed out the high prevalence of antioxidants in the fruit, providing finger lime growers and suppliers with potential to enter health food markets.

    This fruit, which is native to Australia, has only in the last several years become commercially available to growers across the US, after first having been cultivated in California in late 1960s. In fact, nearly all of the current production in the U.S. is in central and southern California and the big island of Hawaii. There are only about 15,000 trees, which are owned by less than a dozen growers. So, there is room to expand production especially by Florida growers, who supply East Coast markets. Prices are quite elevated for the fruit; for instance, during the spring of 2020 finger limes were priced at $32 for 80 grams or 8 limes on Amazon or $18 for 9 to 10 finger limes from one of the only suppliers in South Florida. Questions remain whether these prices will remain elevated as more and more growers enter the market.

    Over the next two years, we at the University of Florida will be exploring the potential for finger limes in these markets and how to develop inclusive supply chains to improve the participation of all growers in them. We will hold taste testing panels and interviews with suppliers, chefs, and bartenders at trade fairs to introduce them to the product, gauge their interest in the fruit, and estimate their willingness to pay for finger limes. The analysis of this research will allow us to estimate the potential demand of the fruit and how many growers could participate in this market. Additionally, we will examine the supply chain to determine which factors need to be addressed to improve growers’ access to these growing markets. Please be on the lookout for further updates as we examine the potential growers to tap into growing finger lime markets and determine what can be done to sustain the demand for them. — By Trent Blare (tblare@ufl.edu), Assistant Professor in Food Resource Economics, University of Florida

  • Fusarium Wilt of Watermelon 2021

    Last year we had a lot of watermelon fields infected with Fusarium from Winterhaven to Yuma, Wellton, and Mohawk Valley. Rain, and overwatering of fields when plants set fruits might have contributed to the disease development.

    Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum, is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult.

    Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields.

    Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting.  Wilting is followed by a yellowing of the leaves and finally necrosis.  The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time.  Affected plants that do not die are often stunted and have considerably reduced yields.  Under high inoculum pressure, seedlings may damp off as they emerge from the soil.

    Initial infection of seedlings usually occurs from chlamydospores (resting structure) that have overwintered in the soil.  Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge.  Infection may be enhanced by wounds or damage to the roots.  The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia.  Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen.

    Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management. — By Bindu Poudel, University of Arizona Extension