Early warning devices seen for citrus diseases

Plant scientists and engineers are developing early warning devices to signal diseases and pests of plants in the same fashion as canaries were once used to alert coal miners to harmful gasses.

But unlike the birds that simply stopped chirping and died in the presence of small amounts of methane or carbon monoxide, the new “smart” technology lives on to reveal much.

One of the researchers, Abhaya Dandekar, professor of genetics at the University of California, Davis, spoke on the concept during a recent seminar for citrus growers at Exeter.

The detection is based on genetic responses used by host plants to communicate stress caused by diseases or pests. The responses are measured by highly sensitive, electronic devices which read the “biomarkers,” or volatile organic compounds, released by plants when they are under attack.

Plants also emit scents when under stress from environmental problems, such as excessive heat and cold, or inadequate nutrients.

Dandekar and colleagues at UC Davis are refining a device known as a differential mobility spectrometer. A compact, economical, and artificial “nose” to sniff out the volatile organic compounds, it uses the same principle as equipment used in the oil industry, explosives and narcotics detection at airports, and biological-chemical warfare.

Another type of device analyzes prepared samples from the host plant to identify stressors.

The hardware exists, so now the task is to learn to recognize responses by the plant, in this case — citrus. USDA scientists at Beltsville, Md., are making progress in detecting responses to citrus canker, huanglongbing, and other serious diseases in isolated laboratory settings. Practical applications are anticipated within a decade.

Dandekar said researchers intend to decipher host plant symptoms at the molecular level, “so we can detect a disease at a much earlier stage for better control of it.”

He conceded, with some diseases, once symptoms are evident, it may be too late to save the plant. However, in the future, robotic devices may even be able to detect the volatile organic compounds released by insects that vector plant-threatening pathogens or feed on plants.

The “electronic nose” technology promises to be a major breakthrough for disease management, and Dandekar said integrating genetic responses with electronics and robotics could also provide “much smarter” robot devices used for various tasks.

Also on the program was a progress report on vision-based robotic harvesting of citrus from Tim McConnell, project manager with Vision Robotics Corp. The San Diego-based company deals with robotic equipment for agriculture, consumer, and military applications.

McConnell’s developmental work, in partnership with the Citrus Research Board, includes an experimental robot citrus harvester.

It is keyed to mounting attention to solutions for labor and immigration issues. “The sooner we can get dependable machines in the field, the sooner we will have stability.”

Robots, he said, are dependent on a vision component, and the sharply lower prices of digital cameras have aided the industry substantially. Software developed for electronic games has also advanced the science.

“You need a system that knows where it is at all times and has the intelligence to find its way to all the spots it needs to get to. That’s where the vision side of Vision Robotics comes in,” McConnell said.

For agriculture, the equipment must find the fruit in the trees and make its way from tree to tree. Using stereoscopic vision, the citrus harvesting gear is being developed to map all the fruit on a tree first and then select which fruit on that tree is to be picked.

Early designs of robot citrus harvesters picked the fruit that could be seen, but not the fruit obscured by foliage. It would get only part way through the tree and then turn back to harvest any previously unseen fruit, causing delays as it searched for fruit.

“The answer is to use a scout robot that goes through ahead of the picker to map the location of all the fruit on the tree. It then plans the pathway of the following picking component to get all the fruit. Pickers will have several arms coordinated by a program to get all fruit as quickly as possible,” he said.

This two-phase concept was first used for apple harvesting prototype equipment, and it can also be applied to vineyards for pruning, spraying, or thinning.

But growers who’ve learned of the equipment have suggested additional tasks could be done by the scout component all through the growing season, not just harvest time.

Potential uses include counts and sizes of fruit to estimate yield, and locating portions of an orchard that need more water or fertilizer.

Observers have expressed interest in combining research on sensors for volatile organic compounds. The result might be, McConnell said, robots with such sensors on their arms to gather all sorts of information about tree health or pest control. Much of the research is done with computer simulation software to save costs.

Integration of GPS technology is planned to guide the robots precisely thorough groves with virtually no supervision.

The economics of robotics are also being evaluated, and he said indications are that there is strong potential for them to be as reliable and economical as hand labor.

The importance of only using clean budwood only was underscored during the seminar by Georgios Vidalakis, director of the California Citrus Clonal Protection Program (CCPP) at UC Riverside.

The industry already faces serious exotic pests and diseases such as citrus canker, huanglongbing, brown citrus aphid and Asian citrus psyllid; another half-dozen or so could rush in quickly without safeguards.

He reminded growers not to try to bypass the program because doing so will harm everybody. Among potential threats from Brazil alone are sudden death, which causes an estimated $40 million in losses each year, and citrus canker and black spot, which each cause $10 million in damage every season.

“Diseases don’t fall out of the sky,” Vidalakis said. Introduction of infected plants can occur virtually overnight with rapid transportation, and the citrus industry, particularly because the crop is perennial, needs to be vigilant to these incurable diseases.

Established more than 50 years ago, the CCPP includes disease diagnosis and pathogen elimination which is later maintained by true-to-type, primary citrus propagation material for leading scions and rootstocks.

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