- Author: David Karp
Talon, M.; Caruso, M.; Gmitter Jr., F.G. eds. 2020. The Genus Citrus.
Woodhead Publishing. 538
pp. ISBN 978-0-12-812163-4.
https://doi.org/10.1016/C2016-0-
02375-6
Information overload is a signature dilemma of our age. For example, Google
Scholar displays 35,000 results for “citrus” from the past year. How can anyone keep up? To the rescue comes The Genus Citrus, a hefty tome edited by Manuel Talon, Marco Caruso and Fred G. Gmitter Jr., and written by an international dream team of contributors, offering an up-to-date overview of 24 topics from genomics to economics.
Chapter 1, “The citrus genome,” describes the rapid progress made in the past two decades in sequencing ten types of citrus, how this allows scientists to distinguish pure from admixed species and a brief but intriguing account of the evolution and domestication of mandarins. It's largely comprehensible to general readers, although many may not be familiar with every word (“pseudomolecules,” “panmictic”).
Chapter 2 integrates recent scientific articles into a readable account of citrus origins – how citrus originated on the border of China, India and Myanmar; how, when and where the various citrus types evolved and spread; and how they're related to each other. Anyone with the slightest interest in citrus should find this fascinating.
Recent genomic discoveries have sowed taxonomic confusion by confirming that many important citrus types actually are admixtures of species. Chapter 4 proposes a new trinomial nomenclature that adheres to the genetic evidence, but also incorporates familiar usage. For example, orange, Citrus sinensis in the standard Swingle system, becomes Citrus × aurantium var. sinensis L. It makes sense and is easy to use, but the official rules of taxonomic nomenclature require strict adherence to precedent, and it remains to be seen whether this, or the new U.S. Department of Agriculture taxonomy or another system will gain traction.
Among the following chapters are authoritative accounts of scion and rootstock varieties, traditional and genomic breeding, biotechnology, fruit growth and development, pests and diseases, post-harvest, flavor chemistry and health effects. Most include plentiful literature citations. The book generally is well written but could have used a good copy editor to correct occasional typos and refine the writing of authors whose first language is not English. Overall, because of its scope and expertise, this is one of the most important citrus publications since The Citrus Industry (5 vols., 1967-1980).
The Genus Citrus is available in both print and online editions, the latter free to those who have access to the University of California library system at https://www.sciencedirect.com/book/9780128121634/the-genus-citrus
For those interested in volumes I and II and Chapter 5 of Volume V of The Citrus Industry check out: The Citrus Industry
- Author: Ben Faber
It turns out, specially trained dogs can find citrus trees infested with Asian Citrus Psyllid (ACP). Canine Detection Services in Fresno has a grant from USDA to provide dogs that will sniff out the insects. The grant runs until March 2022.
The dogs are trained to sniff out ACP using training aids which contain ACP scent which does not have the bacterium causing the disease. The dogs run a pattern within an orchard or along the perimeter of the orchard. Dogs will sniff all sides of the trees in a given pattern. Depending on the environmental conditions, the dogs can smell the psyllid within 22 feet of an infested tree.
Canine Detection Services is also working with CDFA inspectors in residential neighborhoods, according to Victoria Hornbaker, director of the Citrus Pest and Disease Prevention Division within the CDFA. In this instance, the dog handlers shadow CDFA inspectors as they survey residential citrus trees for the pest and disease.
Hornbaker says the dogs can be a valuable tool for state inspectors to survey neighborhoods more quickly. If a dog alerts on a tree, inspectors can investigate for ACP adults or nymphs, and collect insect samples. This is also done in conjunction with surveys for the HLB disease.
The dog team services are free to commercial growers in California, Arizona, and Texas through next March, according to Finke. To schedule a visit or for answers to specific questions, contact Lisa Finke by email at lisa@canine-detection.com.
- Author: Ben Faber
ARS Citrus Rootstocks: A Success Story
The United Nations General Assembly designated 2021 as the International Year of Fruits and Vegetables. This issue of Down on the Farm takes a look at one of ARS's major contributions to fruit production: citrus rootstocks.
Remember that old commercial that declared, "A day without orange juice is like a day without sunshine"? Thanks to the Agricultural Research Service (ARS), consumers can enjoy "citrus sunshine" whenever they like. Begun by USDA more than a century ago, the citrus research program has helped to ensure a bounty of not only oranges, but also grapefruits, mandarins, lemons, and more.
Orange tree leaves with symptoms of Huanglongbing (HLB), also known as citrus greening disease. (Photo by Tim Gottwald, D2259-1)
But that bounty was severely threatened in 2005 with the appearance of a new and destructive disease. Citrus greening, or huanglongbing (HLB), has caused Florida citrus production to plummet around 70 percent in the 15 years since the disease hit U.S. citrus groves. HLB, which causes low yields, yellowed leaves, and bitter-tasting fruit, is caused by a bacterium, Candidatus Liberibacter asiaticus. So far, there is no cure.
Like other crops, citrus crops are susceptible to a variety of diseases and pests. One reliable way to fend off those threats is to graft the fruit-producing part of a tree (the scion) to the lower trunk and root system (the rootstock) of a different tree that has been bred to resist the disease or pest. Rootstocks are also used to obtain specific tree sizes, yields, and fruit quality, among other goals.
A 6-year-old Owari Satsuma Mandarin tree on US-942 rootstock developed by ARS. In this trial, US-942 was the highest yielding rootstock, averaging more than 300 pounds of fruit per tree. (Photo by Jake Price, University of Georgia, D4632-1)
With ARS's long history of helping growers keep their groves healthy and productive, the agency had the expertise required when HLB appeared. To quickly address the problem, the ARS citrus breeding project was refocused in 2005 partly to develop new, HLB-tolerant, highly productive citrus rootstocks.
Led by Kim Bowman, a plant geneticist in the ARS Subtropical Insects and Horticulture Research Unit in Fort Pierce, FL, the team released 12 new HLB-tolerant citrus rootstocks between 2007 and 2018. Before and after the releases, Bowman conducted dozens of field trials to evaluate and validate the rootstocks' performance, providing the scientific data needed to demonstrate their potential and gain industry acceptance. These rootstocks, all with the prefix “US,” have since become a key component in the survival of the Florida citrus industry.
ARS plant geneticist Kim Bowman in front of 5-year-old Valencia orange trees on HLB-tolerant rootstocks he and his colleagues developed. (Photo by Diane Helseth, D4631-1)
Not surprisingly, demand for the rootstocks was extremely high, and growers also needed assurances that they'd be getting the real deal. Bowman arranged for the plant material to be certified disease-free by the Florida Department of Agriculture, paving the way for the rootstocks to be commercially propagated on a large scale.
Bowman and his colleagues have also done a great deal of research on rootstock propagation. Even though most common citrus rootstocks can be grown uniformly from seeds, it takes several years for a young tree to produce a lot of seeds, and the seeds of many new rootstocks don't grow into true-to-type plants. The scientists have shown that using plant cuttings or tissue culture is an acceptable alternative to starting new rootstock trees from seed, and it's a much faster way to create hundreds of thousands of plants.
The use of these alternative methods has dramatically increased propagation for some of the new rootstocks, so that nurseries are not limited by seed supply.
From 2018 to 2020, the HLB-tolerant "US" rootstocks were used to produce nearly 3 million new citrus trees, or about 37 percent of all trees propagated in Florida. These rootstocks have also proven effective in areas affected by other diseases besides HLB. The rootstock "US-942" demonstrated the most consistent outstanding performance in field plantings and was the most popular rootstock in Florida from 2018 to 2020, with about 1.8 million trees propagated during that 2-year period, or about 22 percent of all propagations.
For more information, visit Citrus Rootstocks.—By Sue Kendall, ARS Office of Communications.
A 6-year-old Owari Satsuma Mandarin tree on US-942 rootstock developed by ARS. In this trial, US-942 was the highest yielding rootstock, averaging more than 300 pounds of fruit per tree. (Photo by Jake Price, University of Georgia, D4632-1)
- Author: Ben Faber
Evolutionary ecology of climacteric
and non-climacteric fruits
Published:15 September 2021https://doi.org/10.1098/rsbl.2021.0352
Fleshy fruits can be divided between climacteric (CL, showing a typical rise in respiration and ethylene production with ripening after harvest) and non-climacteric (NC, showing no rise). However, despite the importance of the CL/NC traits in horticulture and the fruit industry, the evolutionary significance of the distinction remains untested. In this study, we tested the hypothesis that NC fruits, which ripen only on the plant, are adapted to tree dispersers (feeding in the tree), and CL fruits, which ripen after falling from the plant, are adapted to ground dispersers. A literature review of 276 reports of 80 edible fruits found a strong correlation between CL/NC traits and the type of seed disperser: fruits dispersed by tree dispersers are more likely to be NC, and those dispersed by ground dispersers are more likely to be CL. NC fruits are more likely to have red–black skin and smaller seeds (preferred by birds), and CL fruits to have green–brownish skin and larger seeds (preferred by large mammals). These results suggest that the CL/NC traits have an important but overlooked seed dispersal function, and CL fruits may have an adaptive advantage in reducing ineffective frugivory by tree dispersers by falling before ripening.
https://royalsocietypublishing.org/doi/10.1098/rsbl.2021.0352
/h1>/h1>- Author: Petr Kosina
New online course on diagnosing herbicide injury now available
—Petr Kosina, UC Statewide IPM Program
A brand-new online course on Diagnosing Herbicide Injury focusing on how an herbicide injury situation can arise, what information can help diagnose symptoms during field investigations, and what tools are available to you, is now available from the UC Statewide Integrated Pest Management program (UC IPM).
When unexplained damage is noticed on a crop or other non-weed plant, herbicides are often a primary suspect. That is no surprise because herbicides are very powerful and effective tools used to control weedy plants in a wide variety of locations. However, symptoms of many other plant stresses, such as diseases and nutrient deficiencies or toxicities, can closely resemble the injury symptoms caused by herbicides. Economic implications of herbicide damage can vary–in some cases visible injury may have very little direct economic effect while in others, even slight herbicide symptoms can affect the marketability of affected plants. In addition, the presence of an unregistered herbicide on non-target crops can result in illegal residues which could have both safety and legal consequences.
The new online course was developed by Dr. Brad Hanson and Dr. Kassim Al-Khatib from the Department of Plant Sciences at UC Davis, and UC IPM instructional designers. If you are a grower, pest control adviser, or pesticide applicator, then this course is a great opportunity to learn about how to approach crop injury investigation when herbicide is suspected cause. You will learn how herbicides injure plants, how long herbicide symptoms may last and factors that may influence the time that herbicide injury symptoms are visible, possible scenarios of herbicide exposure based on uniform and variable injury patterns observed in the field, how to prepare samples for the laboratory analysis and more.
The course content is free to anyone who wishes to view it. For those requiring a certificate of completion and continuing education units (CEUs), the regular cost is $30, but we are offering a reduced price of $15 through October 31, 2021. Diagnosing Herbicide Injury course has been approved by the California Department of Pesticide Regulation (DPR) for 1.5 continuing education units (CEU) of Other, Certified Crop Advisor (CCA) for 1.5 units (IPM), and the Arizona Department of Agriculture for 1.0 Credit.
If you are a DPR license or certificate holder with a last name beginning with letters M through Z, then this will be your year to renew. Now is a good time to check out the other UC IPM online training courses offered. All are 50% off the regular price through October 31st. DPR strongly suggests returning renewal packets back to them by October so that your license or certificate can be renewed before it expires. Many of our courses are accredited by DPR for continuing education hours and also by the California Structural Pest Control Board (SPCB), Certified Crop Advisor (CCA), the Western Chapter of the International Society of Arboriculture (WCISA), and the Arizona Department of Agriculture.