Recently, I read an article in "Fresh Plaza" about the arrival of large amounts of 'Kinnow' mandarin fruit from Pakistan. http://www.freshplaza.com/article/117470/Discover-Pakistani-kinnow-mandarins-at-Fruit-Logistica-2014#SlideFrame_1
This is a country that is surrounded by countries with huanglongbing. It's also the country where Mark Hoddle, Biocontrol Specialist from UC Riverside, collected Tamarixia radiata , the tiny wasp that is helping control Asian Citrus Psyllid. Pakistan has invested heavily in juice plants just for this industry which was established with this selection that came out of the Citrus Research Station breeding program in the 1930's. It makes me wonder if there might be a significant tolerance to this citrus disease in this mandarin variety. There has been a lot of work by both USDA and U. of Florida evaluating citrus varieties for tolerance to HLB. A wide range of tolerances have been noted. Fred Gmitter along with others are involved with this work and find that under different climatic conditions, resistance can vary. In the 'Kinnow' variety, it looks like there is hope in finding a variety that can be used to breed tolerance into other varieties. The fruit itself is noted for its juiciness and sweetness. But as you can see from the photo, it's got a lot of seeds.
|USDA Creates Multi-Agency Emergency Response Framework to Combat Devastating Citrus Disease|
|USDA Providing $1 million to Jump Start Citrus Response Framework|
WASHINGTON, December 12, 2013 - The U.S. Department of Agriculture today announced the creation of a new, unified emergency response framework to address Huanglongbing (HLB), a serious disease of citrus that affects several U.S. states and territories. This new framework will allow USDA and its many partners to better coordinate HLB resources, share information and develop operational strategies to maximize effectiveness.
"USDA listened to the citrus industry's request for more urgency and greater coordination on the response to HLB and is implementing an emergency response structure," said Secretary Tom Vilsack. "To jump start this initiative and affirm our commitment to industry, USDA is also providing $1 million to be used in support of research projects that can bring practical and short-term solutions to the growers in their efforts to combat this disease. Through the Specialty Crop Research Initiative of the Farm Bill, USDA has provided $9 million in research to blocking the ability of insects to spread HLB to healthy trees. We need Congress to quickly pass a new Farm, Food, and Jobs Bill that continues to support this kind of research to protect a crop worth more than $3 billion in the last harvest."
The new framework will bring together USDA's Animal and Plant Health Inspection Service (APHIS), Agricultural Research Service (ARS) and National Institute of Food and Agriculture (NIFA), along with state departments of agriculture and the citrus industry into a Multi-Agency Coordination (MAC) Group for HLB. It will provide industry with a single contact for all the federal and state entities that work on citrus issues and better enable the collective to collaborate on policy decisions, establish priorities, allocate critical resources, and collect, analyze, and disseminate information.
The HLB MAC Group will also help coordinate Federal research with industry's efforts to complement and fill research gaps, reduce unnecessary duplication, speed progress and more quickly provide practical tools for citrus growers to use.
HLB, also known as citrus greening, is named for the green, misshapen, and bitter-tasting fruit it causes. While this bacterial disease poses no danger to humans or animals, it has devastated millions of acres of citrus crops throughout the United States and abroad. In the United States, the entire States of Florida and Georgia are under quarantine for HLB, and portions of California, Louisiana, South Carolina and Texas are also under quarantine for the disease. The U.S. Territories of Puerto Rico and the U.S. Virgin Islands are under HLB quarantines as well.
You can find more information about HLB and the HLB MAC Group on USDA's Multi-Agency Response to Devastating Citrus Disease website.
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The weather is perfect for looking for Asian Citrus Psyllid. There is new flush and that is where the adults go to lay their eggs and feed. This is also the tissue where aphids and scale crawlers will be found, as well.
ACP has been active all this winter, but now is when they are going to be the most noticeable. Get out there and look and alert the CDFA Exotic Pest Hotline to confirm a find, 1-800-491-1899.
ACP adult and nymphs with waxy exudate from nymphs.
At a recent conference on Postharvest Technology Advances, Cristina Davis from the UC Davis Department of Mechanical and Aerospace Engineering presented information on the development of a device that can smell out trees infected with Huanglongbing (HLB).
Scientists at UC Davis are refining a mobile chemical sensor that can detect diseased citrus trees by sniffing their volatile organic compounds (VOCs). VOCs are emitted by all types of plants and contribute to their distinctive odors—such as the perfume of orange blossoms and pungent scent of garlic in the air. VOCs must exist at very high levels for humans to smell them, and there are some VOCs people cannot smell at all. The machine is able to figure out the signature smells of HLB infected trees, sort of the way people evaluate wines with terms like “grassy”, “plum”, or “austere”, and distinguish them from healthy or trees infected by other diseases.
Finding HLB-infected trees and eliminating them before Asian Citrus Psyllid (ACP) picks up the disease and spreads it to neighboring trees is a major challenge. The pathogen in the tree cannot be detected by leaf testing for three to nine months after infection, and the symptoms don’t show up in the tree for a year or more after infection. Meanwhile, the disease can be spread by ACP. Research is under way to develop early HLB detection so that infected trees can be rapidly removed. Early detection will also allow researchers to more rapidly assess treatment programs for controlling not only the spread of the disease, but also possible cures or rootstocks or scion varieties that might have some resistance to the disease.
HLB infected tree showing mottling in one part of the canopy
This February there was a four day international conference in Orlando, FL that attracted 467 people from 21 countries, including about 20 from California. There were 87 oral presentations and over 80 posters that covered all aspects of Huanglongbing, the insect vector (Asian Citrus Psyllid or ACP), disease detection, insect control and monitoring and a whole lot of information on the genome of the bacteria, how it compares to other infectious bacteria and what can be done to exploit its genetics to control the disease. To learn more, the proceedings and agenda can be found at: http://irchlb.org/hlb/schedule.aspx.
To start off, this is an amazing example of coevolution among a plant, a bacteria and an insect. It appears that the citrus tree may give off an odor which at low concentrations acts as an attractant, but at higher concentrations is a repellant. The infected tree also gives off volatile organic compounds (VOCs) that can be used to identify affected trees. These chemicals are not pheromones which are social odors emitted by some insects which act to affect insect behavior, such as mating or causing aggregation. Being able to use these new odors will allow for better methods of monitoring the insect with lures. We currently use blunder traps which are not a very good indication of whether there are ACP present.
Currently the most commonly used technique for identifying infected trees is the use of the polymerase chain reaction (PCR) method which is a biochemical technology that identifies the presents of the bacterial DNA. This method was used on the leaves of trees since that is what the psyllid feeds on and where the bacterial infection starts. Results have been erratic and inconsistent and often would not give results until many months after the infection started.
The bacteria clog the phloem tissue which carries sugar to the roots and on which the psyllid feeds. The higher concentration of sugar accelerates the development of the insect and it can lay more eggs. The bacteria travel down the stem at measured rates of one centimeter per day and accumulate in the root system. The root tips are the growing points and where the plant directs sugar to feed the new root growth. It is from the roots that the bacteria go out to all points of the canopy where it can then be picked up by uninfected psyllids which can then go on to find a new tree to feed on. By measuring root tips, rather than leaves, the detection is more rapid and much more consistent, since the bacteria levels are higher in the tips than the point of infection. Disease detection is now being improved by better understanding of the biology of the infection process and thereby allowing faster determination of whether a treatment works.
The ability to evaluate what treatments work has allowed researchers to determine such things as what rootstocks and scions might be most vulnerable, what spray programs are the most successful and how better to lay out trials. It turns out that there is an edge effect during a psyllid invasion and that the first affected trees are right on the perimeter. By focusing spray programs in this area can slow the movement of the insect to the middle of the orchard.
Actual economic control of this pest and disease are still some time away, but with this new understanding of the disease process we will be closer to finding a solution.
Fruit drop and defoliation associated with HLB