The best time to treat a stressed plant may be just before you can see it’s stressed.The trick is to know when that is. And a University of Georgia scientist may have theanswer.It’s a matter of light, said Chi Thai, a biological and agricultural engineeringscientist with the UGA College of Agricultural and Environmental Sciences.Plants, he said, are trying to tell us when they’re stressed. We just can’t see it.It’s not that we’re not trying. Seeing that plants are stressed earlier than wenormally do could save farmers millions of dollars. We just don’t have the rightequipment.Human Eyes Limited”Human eyes can see only at light wavelengths between 400 and 700nanometers,” Thai said. “For the part of light that gets through the atmosphere,the region of interest to our plant-health research is from ultraviolet wavelengths around200nm to near-infrared wavelengths around 2500nm.”The answer, as Thai saw it, was to improve the equipment. “We’ve built afield-portable spectral imaging system,” he said. “It contains two spectrometerssensitive from 300nm to 1700nm and is equipped with fiber optic inputs and continuouslytunable spectral video imaging capability.”Thai adds some Liquid Crystal Tunable Filters, then a virtual-reality goggle (because acomputer monitor is unwieldy in the field) to see plants in literally a whole new light.Reading Plants’ Chemical Signatures”This equipment allows human users to visualize chemical signatures of a plantwhich usually are beyond unaided human vision,” Thai said. The chemical signals letpeople see the plant’s earliest signs of stress.Thai took the process a step further, with an LCTF alternating between two fixedwavelengths, 692nm and 755nm. By plotting the average of the gray values of the pixelsforming the plant canopy image, he can directly estimate the chlorophyll and biomassamounts in plants.”The plant-health status was related to the degree of brightness of theimage,” Thai said. “A brighter plant is a healthier plant.” With his portable spectral imaging system, Chi Thai is able to see plant health in a whole new light. The black-and-white images resulting from Thai’s research show stark contrasts between the healthy plant on the left and the stressed plant on the right. Images: Chi Thai Photo Courtesy of Chi Thai Thai’s initial, encouraging research was on Bahia grass and bush beans. Now he’sstudying peanut plants inoculated with Tomato Spotted Wilt Virus.The biggest trouble so far has been getting the virus to infect the plants. “Forsome reason, what happens naturally very easily in the field has been hard for us to do inthe lab,” he said.Research Could Help GrowersIf the studies work, though, it could greatly help growers of the state’s $400 millionpeanut crop, said Albert Culbreath, a CAES plant pathologist in Tifton, Ga.”It would help first in research,” Culbreath said. “It would be anice tool for evaluating plants in greenhouse and small-plot studies.”Many plants don’t show symptoms right away but turn yellow and wilt late in the season.”Such a tool might enable us to know what’s really going on in those plants,” hesaid.”In epidemiological studies,” he said, “detecting infection beforesymptoms occur might help pinpoint when management actions might be taken to reduce the… disease.”Many Potential BenefitsSpectral imaging could help evaluate varieties and management practices, too. If itcould help farmers assess disease problems faster than they can by seeing symptoms, itcould help even more.”If we could come up with a chemical signal for assessing problems that could bedetected from a few feet above or a mile overhead,” Culbreath said, “it could beof economic value.”It may help farmers boost their yields, he said. And even if it can’t, it may be ableto better predict losses, which would help growers in their marketing.For the time being, all the scientists really know is the potential.”We don’t know what reality can be, or how much benefit,” Culbreath said.”There’s much work to be done, but new tools such as this can be of great importancein the future.”
A New Light.