Jacob Price, 2013 Friends of IPM Award Winner
Graduate Student, Ph.D. category

Jacob PriceFriends of IPM Graduate Student Award winner Jacob Price was a student employee working in the diagnostic lab at the Texas A&M AgriLife Research Center, Amarillo TX when he first encountered Wheat streak mosaic virus. Although he diagnosed other plant diseases, wheat streak mosaic seemed to prompt a question every time he diagnosed it for a grower: “Should I water?” It was very common for producers to state, “I thought it was drought stress, so I started irrigating and the wheat just died.”

Vectored by a tiny mite called the wheat curl mite, wheat streak mosaic is a serious disease of wheat that often blindsides producers in the arid conditions of northern Texas. The mite is so tiny that it can be seen only with a dissecting scope, so producers cannot scout for it. Once the disease begins to show symptoms, which include a mosaic yellow streaking pattern and stunting, nothing can be done to cure the infection and at this time it is unknown if any chemical applications can be used to limit the disease. Producers in Texas can lose $464.5/ha to $118.1/ha depending on the amount of irrigation applied and up to $60.1/ha during dryland production to the disease in a year (Velandia, et al., 2010). The mite and disease affect wheat production throughout the Midwest as well and often losses can be severe.

Because of the dry conditions in Texas, disease symptoms look similar to drought or nutrition stress, so growers usually increase irrigation and nitrogen inputs. We noted that wheat samples that had succumbed to the virus had a much smaller root system, said Price, leading him to question whether the diseased plants were even taking up the additional water added by irrigation. Further examination of the soil proved that they were not; the water was simply staying in the soil.

Price is the recipient of the Southern IPM Center’s first Friend of IPM Graduate Student award, Ph.D. category. He will be receiving his award next February at the Southern Regional American Phytopathological Society meeting in Dallas, Texas.

Price began his college studies in Biological Sciences at Amarillo College in Texas, and after he received his associate’s degree, he met Dr. Nabarun Ghosh from West Texas A&M, who introduced him to Dr. Charlie Rush, project leader in Plant Pathology at the Texas A&M AgriLife Research Center. Dr. Rush gave him a job in the diagnostic lab at Texas A&M AgriLife as a student worker. While working, Price finished his Bachelors and Masters at West Texas A&M and was promoted to Technician and eventually to Senior Research Associate. Price now is the plant disease diagnostician for wheat viral diseases in the Plant Diagnostic Clinic at the Texas A&M AgriLife Research Center in Amarillo, which is part of the Great Plains Diagnostic Network.

The question of water efficiency had never been studied, so Price dedicated his master’s work to explore how efficiently infected plants were using water, since one of the first reactions to disease symptoms was to shower the plant in water to counteract suspected effects of drought. In his experiment, he used two varieties, one susceptible and one resistant. He inoculated half of the plants with wheat streak mosaic and exposed them to one of three different water treatments: full irrigation, medium irrigation, and irrigation deficiency. During the study, Price found that once wheat became infected with wheat streak the root systems became stunted upwards of 50%. It was also found that after irrigation a large amount of water was left in the soil profile demonstrating that the stunted root systems of infected plants were not able to uptake the water as efficiently as healthy plants and the water was lost to production. “The loss of these additional inputs only increases the loss in return to wheat production,” said Price. The resistant variety was able to maintain root growth and water use during the experiment, however the variety used is not in production due to quality and threshing issues.

Jacob Price in labDue to a disease gradient that is created by movement of the wheat curl mite throughout infected fields, the future direction of this research is to determine the point at which irrigation becomes futile, so growers could use their irrigation more effectively on the portion of the field that would produce a yield. “We hope to be able to recommend to growers to limit irrigation on particular diseased areas of the field,” Price says.

Eliminating irrigation of infected plants could save farmers approximately $12,000 or 28.6 million gallons of groundwater per year.

He also studied the relationship of temperature and disease inoculation on different wheat varieties that were resistant to wheat streak mosaic. “In the northern Texas Panhandle wheat is typically planted early in the fall as a dual purpose crop for both grazing and grain production,” stated Price. The wheat streak resistance trait is temperature sensitive and becomes inactive when temperatures are above 75 degrees, so when growers plant their seed in the early fall, the temperatures were too high for the resistance trait to combat the virus. The wheat curl mite tends to collect on “volunteer wheat” during the summer, so when the new crop is planted in late August and early September, the mites move to the crop and infect the plants.

“We wanted to determine if these resistant varieties had the ability to recover during winter dormancy after initial infection in the early fall by infesting the different varieties with viruliferous wheat curl mites at high temperatures and then exposing them to low winter temperatures,” said Price.

None of the resistant varieties were able to recover after initial infection with the virus at warm temperatures, therefore they could not be used for early dual purpose planting in the fall. However, it is important to note that the resistance is temperature sensitive and the varieties do contain adequate resistance as long as the temperatures remain low.

An unexpected finding of the study, one variety--TAM 112--was found to be resistant to the curl mite. “We infested TAM 112 wheat with the wheat curl mite and found out that throughout the study it contained significantly less mites than the other varieties tested. This showed that TAM 112 contains an unknown resistance to the curl mite,” Price says. “We are now working with other departments to determine the source of the resistance found in TAM 112.”

The resistance to the wheat curl mite found in TAM 112 is critical to preventing a relatively new disease: Triticum mosaic virus, which displays symptoms identical to those of wheat streak mosaic but is not deterred by wheat streak resistant varieties. The disease was discovered in Kansas in 2006, during wheat streak resistance trials. But it is believed to have been in the US for much longer.

“If you use a wheat streak resistant variety, it’s still susceptible to Triticum mosaic virus,” says Price. “That’s why TAM 112 is so important, because if we can use a variety resistant to the mite, it’ll have less of a chance of getting either virus.”

Price and his colleagues are looking into ways to combine resistant varieties with mitacide applications. However, no mitacides are currently labeled for wheat curl mite.

Price is currently working on a Ph.D. through the Plant and Soil Sciences Department at Texas Tech University. His dissertation study involves movement of the wheat curl mite and disease spread of Wheat streak mosaic virus and Triticum mosaic virus.

In addition to doing virus diagnostics for the GPDN lab, Price holds workshops for farmers on wheat virus management, teaches farmers how to manage diseases and is a part time instructor in Biological Sciences at Amarillo College.

Reference:
Velandia, M. Rejesus, R. M., Jones, D. C., Price, J. A., Workneh, F., and Rush, C. M. 2010. Economic impact of Wheat streak mosaic virus in the Texas High Plains. Crop Protection 29:699-703.