Leaf


	Issue 106 Prairie Grains


	Prairie Grains is the official publication of the Minnesota Association of Wheat Growers, North Dakota Grain Growers Association, Montana Grain Growers Association and South Dakota Wheat, Inc.




	2010 University of Minnesota - Special Report


	Bacterial Leaf Stripe of Wheat:


	An Emergent Problem in Need of Solutions


	Carol A. Ishimaru1, Deborah Samac1,2, and Ruth Dill-Macky1

Bacterial leaf streak (BLS) of wheat has been evident in Minnesota, North Dakota and South Dakota in the past three cropping seasons. While generally sporadic in nature, the levels of BLS observed suggest that this disease may be of increasing concern for wheat production. As little research has been conducted on BLS, preliminary research is necessary to establish the severity of the problem, determine the impact of BLS on grain yield and quality, and develop the tools to work effectively with the pathogen. It is essential that we undertake this research before committing resources to a long-term effort in disease control, including plant breeding.

Bacterial leaf streak, caused by Xanthomonas translucens pv. undulosa, results in distinctive symptoms on leaves and glumes. Although BLS can be severe, the impact on yield and quality is not well understood. As with most plant diseases, breeding for resistance is likely to be the most effective and economic control strategy, however preliminary research is essential to develop the techniques to work effectively with this pathogen system and to establish the importance of BLS to wheat production in the Upper Midwest.

Several possible explanations could account for the noticeable upsurge of BLS within the region. One compelling possibility is that newly released varieties may have inadvertently introduced susceptibility to the disease. Other explanations for the disease increase could be that the pathogen itself has evolved, becoming better adapted to the region and current varieties. There also might be other pathogens associated with the disease symptoms, which can be grouped generally into cereal leaf streak disease. Changes in crop residue management may also be influencing the situation by creating greater reservoirs of inoculum. The recent reductions in fungal diseases have likely enabled better detection and yield loss estimates for BLS. This project will provide resources for examining some of these possibilities while advancing longer-term disease management strategies.

Since its initiation in summer 2009, most of the focus and progress has been on obtaining a representative collection of virulent strains of the BLS pathogen from Minnesota. Wheat samples were collected from seven locations in Minnesota. Bacteria were isolated on either nutrient agar or a semi-selective medium (XTS). A total of 66 strains were purified and stored for further characterization and pathogenicity studies. Further bacterial collections will be made in 2010.

Pure strains of bacteria from wheat plants were tested using a PCR assay for the presence of a DNA sequence in the ribosomal DNA that is specific to cereal leaf streak pathogens. Of 39 strains tested, 13 strains were positive by the PCR assay. The 16S ribosomal DNA from the 13 positive strains was amplified, sequenced, and used to search for the closest matches in GenBank. The closest related sequence was to Xanthomonas translucens pv. poae.

A quantitative real-time PCR assay using SYBR Green was developed to quantify any cereal leaf streak bacteria. The assay is based on amplifying and quantifying the ribosomal sequence specific to cereal leaf streak bacteria. DNA was isolated from two strains of CLS bacteria and used in the assay. The assay reliably detects as few as 10 bacterial cells. The range and sensitivity of the assay was retained in the presence of wheat DNA. These results show that the assay will be useful in detecting and quantifying CLS bacteria from infected wheat plants. Experiments are in progress to compare results of the quantitative real-time PCR assay to traditional agar plate counts of bacteria isolated from infected wheat leaves.