Christina Cowger, Small Grains Pathologist

Dr. Cowger investigates the biology, epidemiology, and population genetics of economically important small grain pathogens. Her goal is to contribute to improved, sustainable management practices. Her program interacts closely with breeders, extension personnel, and other pathology and population genetics groups in the U.S. and beyond.

Lab members March 2021

Dr. Cowger has expertise in pathogen adaptation to host resistance; host genotype diversity and its effects on pathogen populations; small-grain disease diagnosis and management; and epidemiological and management implications of pathogen population structure.  Her group conducts research in the laboratory, greenhouse, and at multiple field locations. The lab uses molecular techniques to investigate species identity, phylogeny, population structure, and host-pathogen interactions. Classical field-plot research are also carried out.Three examples of current research:

*A novel discovery was made concerning wheat powdery mildew resistance gene Pm1a.  This gene provides resistance to Blumeria graminis f. sp. tritici (Bgt), the fungus that causes wheat powdery mildew. Pm1a has had greater-than-expected durability in the U.S., and when virulence to it has appeared, it has been surprisingly short-lived.  A study of virulence to Pm1a was conducted using 216 Bgt isolates from six countries.  It revealed that a single previously identified effector gene (AvrPm1a) on Bgt chromosome 6 was insufficient by itself to explain global patterns of virulence and avirulence to Pm1a.  A genome-wide association study revealed a second effector locus on a different Bgt chromosome that also interacts with Pm1a.  Mutations at both loci are necessary for virulence.  This highly unusual discovery was confirmed by a co-expression experiment, and the results were published in New Phytologist.  The two-effector model for virulence to Pm1a is likely at least a part of the explanation for the greater durability of Pm1a in the U.S.  Machine learning is being examined as a way of studying the two-gene model.

*Fusarium head blight (FHB), also known as scab, is a fungal disease that attacks small grains, contaminating the grain with the mycotoxin deoxynivalenol (DON), a toxic compound also known as vomitoxin. For barley, the most common grain used to make malt for beer and spirits, even a small amount of DON can cause crops to be rejected by purchasers.  In a four-year study, the Raleigh PSRU team assessed three different fungicides for FHB reduction. They also evaluated the level of DON in mature winter barley heads following a fungicide application at one of three growth stages – half heading, full heading, and six days after full barley head emergence.  The latest fungicide timing reduced DON significantly more than the early timing for all three fungicides tested. Applying fungicide before all heads were emerged did not significantly reduce DON in winter barley as compared to not spraying at all. If scab is threatening, growers should wait about six days after barley heads have all appeared before applying fungicide. The results were published in Plant Disease and ARS put out a media release.

*In North America, FHB is primarily caused by Fusarium graminearum. Conventional management relies on moderately resistant wheat cultivars and fungicides, while efforts to identify an effective biocontrol agent (BCA) have not met with commercial success. A previous study showed that Fusarium poae, a weak pathogen, reduced DON accumulation by more than 50% in bread wheat when applied before inoculation with F. graminearum in a growth chamber. We are testing the effectiveness of F. poae and another weak pathogen, F. acuminatum, in decreasing FHB symptoms and DON in winter wheat when the weak fusaria infect wheat in the greenhouse or the field simultaneously with F. graminearum or two days prior. Initial results in both settings are promising.