Weather across southeastern Texas and Arkansas rice fields this year caused something other than the tasty grain to crop up – panicle blight.
The condition affects rice plants in the field, and while it does not pose a problem for human consumption, it does take a bite out of the harvest.
Two types of blight can affect rice, according to Dr. Ted Wilson, director of the Texas AgriLife Research and Extension Center in Beaumont. Panicle blight can be caused by environmental stress such as high temperatures and need not involve a plant pathogen, he said, while bacterial panicle blight is caused by bacteria.
"The bacteria that causes bacterial panicle blight exists in the environment. It's seed-borne," said Dr. Xin-Gen "Shane" Zhou, Texas AgriLife Research plant pathologist in Beaumont. "During years in which panicle blight is severe, losses in rice fields can be as high as 40 percent of the potential yield."
This year high nighttime temperatures accompanied by frequent rainfall and 95 percent humidity while the rice crop was heading and flowering sparked development of bacterial panicle blight.
"A number of rice farms in Jefferson, Colorado, Chambers and Wharton counties of Texas had significant losses due to panicle blight," Zhou said. "And that region accounts for about 60 percent of the total rice production in the state. Panicle blight was also found in various research plots and affected several different varieties of rice."
Zhou said bacterial panicle blight, which was first described in Japan in 1967, is now known to exist in China, Korea, Latin America, the Philippines and Vietnam as well as the U.S., where it was first identified in 1996. It is caused by the bacterium Burkholderia glumae.
The disease form of panicle blight occurs sporadically on individual plants, Zhou said, or can appear in circular or oval patterns across a field. Florets infected with bacterial panicle blight are discolored from light green to light brown on the base then reddish-brown in the middle. The upper portion later turns straw colored. The disease can cause linear lesions on the sheaths and lead to sheath or stem rot.
Bacterial panicle blight spreads primarily by splashing and wind-blown rain, he added.
"The bacterium invades germinated seeds, inhabits the roots and lower sheaths, and moves up the growing plant," Zhou said. "The bacterium colonizes and multiplies in spikelets quickly by using the sugars developing in the grains."
Because the disease does not occur in yield-cutting levels most years, little is known about the disease’s cycle, treatment or prevention methods, Zhou said.
The plant pathologist conducted two trials this season and has begun culturing the disease in his laboratory in hopes of learning more about the organism.
"At this time, there is no chemical control, though seed can be treated," Zhou said. "Proper cultural practices, including early planting or use of early maturing varieties, can help by avoiding the hottest part of the growing season."
Zhou also said not planting excessive amounts of seeds per acre and reducing nitrogen rates have helped reduce damage from this disease.
Ultimately, he hopes additional preventive and treatment methods will be found through his lab experiments to help farmers in years when climatic conditions prompt the occurrence of bacterial panicle blight.