Texas: Hot and Humid Nights Decrease Rice Yield and Quality
So far this season, I have had very few calls regarding rice insect pests. In fact, I have had many more questions about urban insects like termites, chiggers, honey bees, and garden and pantry pests. Late rice planting may be responsible for the lack of recent rice insect calls. But we can always hope our bad insect critters will be at a low ebb this year! Only time will tell.
Because of late plantings in Texas this year, we may expect more panicle blight problems which are associated with high day and night temperatures during flowering—so, later plantings flower later in the summer when temperatures are typically higher. In addition, more and more climatological data suggest climate change, whether caused by man or nature, is a cause for concern. We all know our planet experienced an Ice Age more than 10,000 years ago which was probably due to a small change in the rotational axis of the Earth. Obviously, this was not a result of build-up of greenhouse gases by mankind! Thus, climate change is simply a change in climate without regard to cause. Scientists—Drs. Abdul Razack Mohammed and Lee Tarpley—are conducting proactive research to develop management practices to ameliorate the effects of high day and night temperatures on our rice crops. If higher than normal temperatures occur in the future, the results of this research could be pivotal in dealing with this environmental change.
For scientists, a major challenge is to increase crop production to keep pace with an increasing global population. Furthermore, an increase in global temperature will decrease crop productivity thereby increasing pressure on world-wide food production and supply. As a result of climate change, night temperatures are predicted to increase more than day temperatures. The rice-growing region in the southern U.S., with its hot and humid summers, is susceptible to rice crop yield loss due to an increased frequency of periods with high night temperatures. In addition, southern U.S. rice milling quality is reduced by high temperatures, especially high night temperatures, and appears to be associated with an increase in chalkiness. Given the occurrence of such periods of high temperatures being implicated in rice yield and quality losses in recent years, a combination of altered crop management strategies and crop genetic improvement is needed to minimize both current and intermediate-term effects of climate change on southern U.S. rice production.
Under high night temperatures, rice plants release large amounts of “stress” molecules called “reactive oxygen species,” according to Drs. Mohammed and Tarpley, physiologists at the Texas AgriLife Research and Extension Center at Beaumont. They evaluated rice at a night temperature of 86 degrees Fahrenheit and found that the released oxygen molecules damaged leaf cell membranes and pollen. When plants produce less pollen, they don’t reproduce as successfully. They also found that once leaf membranes were damaged because of the high night temperatures, rice plants did not photosynthesize as much during the day; under high night temperatures, rice yields fell by 20%. The primary effects of high night temperatures on southern U.S. rice yield appear to be due to decreased production of photosynthates, increased consumption of photosynthates (respiration), accelerated rate of plant development, and decreased reproduction. All of these effects are interrelated—high night temperatures appear to trigger heat induced reactive-oxygen-species-mediated degradation of membranes and enzymes (i.e., oxidative stress). Oxidative stress is common to all organisms, underlying, for example, aging and sunburn.
One of the crop management strategies developed by Drs. Mohammed and Tarpley is the application of plant growth regulators at sensitive stages of rice plant development (4 leaf stage, 6 leaf stage and boot) to prevent yield loss. They used plant growth regulators which induce heat tolerance in rice plants by decreasing oxidative stress in various ways. In several studies, they applied the following plant growth regulators: 1-MCP, α-tocopherol, glycine betaine or salicylic acid, all of which increased yield by 10 to 15% under high night temperatures. According to Drs. Mohammed and Tarpley, application of these plant growth regulators helped increase production and decrease consumption of photosynthates while protecting leaf cell membranes and pollen. Certain plant growth regulators have the potential to be commercialized for use in preventing the effects of high night temperatures and other environmental stresses.
Research for the benefit of our rice industry must balance both basic and applied studies to solve both long- and short-term problems. The above research efforts are a good example of this balance.