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United States Department of Agriculture

Agricultural Research Service

Research Project: CHARACTERIZATION OF HOST-PATHOGEN INTERACTIONS IN BARLEY AND WHEAT Title: Identification of Pyrenophora teres f. maculata, Causal Agent of Spot Type Net Blotch of Barley in North Dakota

Authors
item Liu, Z -
item Friesen, Timothy

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 28, 2010
Publication Date: March 5, 2010
Citation: Liu, Z.H., Friesen, T.L. 2010. Identification of Pyrenophora teres f.maculata, Causal Agent of Spot Type Net Blotch of Barley in North Dakota. Plant Disease. 94(4):480.

Interpretive Summary: Net blotch of barley is caused by the fungus Pyrenophora teres and can be differentiated into two forms, net form net blotch (NFNB) and spot form net blotch (SFNB) caused by P. teres f. teres and P. teres f. maculata, respectively. Recently, epidemics of SFNB have occurred in Australia, Canada, and Europe. The North Dakota/Northwestern Minnesota agricultural region leads the United States in barley production with 2 million metric tons produced in 2008. Among the isolates collected from this barley region, one isolate collected in Fargo in 2006 (FGOH06Pt-8) and one isolate collected in Langdon in 2008 (LDNH08Pt-4) were identified as P. teres f. maculata. A pathogenicity test of all isolates was performed on regional barley cultivars and induced typical spot-type lesions but much larger than those produced by other spot type net blotch isoltes, suggesting a higher level of virulence. To our nowledge this is the first report of P. teres f. maculata in the North Dakota/Northwestern Minnesota barley growing region. Resistance to SFNB should now be considered in local barley breeding programs and cultivar releases.

Technical Abstract: Net blotch of barley (Hordeum vulgare L.), caused by the fungus Pyrenophora teres (anamorph: Drechslera teres) can be differentiated into two forms, net form net blotch (NFNB) and spot form net blotch (SFNB). The pathogen forms causing the two different symptoms are P. teres f. teres and P. teres f. maculata, respectively. Recently, epidemics of SFNB have occurred in Australia, Canada, and Europe (1). The North Dakota/Northwestern Minnesota agricultural region leads the United States in barley production with 2 million metric tons produced in 2008. Diseased barley leaf tissue was collected annually from 2004 to 2008 in Fargo and Langdon, ND. Leaves were plated on water agar and incubated at room temperature for 24 h in the dark and 24 h in the light to promote sporulation. Ten monocultures each year from each location were isolated. Among the isolates collected, one isolate collected in Fargo in 2006 (FGOH06Pt-8) and one isolate collected in Langdon in 2008 (LDNH08Pt-4) were identified as P. teres f. maculata. Conidia from the two isolates were similar to other P. teres f. teres isolates. A pathogenicity test of all isolates was performed on the regional barley cultivars Tradition, Robust, and Lacey as well as barley lines Rika and Kombar (3) as previously described (2). Net form isolate 0-1 and spot form isolate DEN2.6 (obtained from Brian Steffenson, University of MN) were inoculated as controls. 0-1 produced typical net type symptoms on all barley lines except the resistant line Rika in which only small dark resistant spots were observed. DEN2.6 produced pin-point spot-like lesions with an extensive yellow halo on Robust, Lacey, Rika, and Kombar, but without chlorosis on Tradition. The two newly identified isolates induced elliptical spot-type lesions measuring 3 × 6mm, much larger than those produced by DEN 2.6, suggesting a higher level of virulence. The internal transcribed spacer (ITS) region was obtained from all isolates using primers ITS1 and ITS4 (4). Additional ITS region sequences from P. teres and P. tritici-repentis (4) were downloaded from NCBI Genbank for analysis. In the sequenced 522-bp region, FGOH06Pt-8 and LDNH08Pt-4 were identical and only a single base pair differentiated DEN2.6. FGOH06Pt-8 and LDNH08Pt-4 grouped in one cluster along with other P. teres f. maculata isolates, while 0-1 grouped with other P. teres f. teres isolates. However, all isolates tested were close genetically, while they were separated from P. tritici-repentis. To our knowledge this is the first report of P. teres f. maculata in the North Dakota/Northwestern Minnesota area. Resistance to SFNB should now be considered in local barley breeding programs and cultivar releases.

Last Modified: 10/21/2014
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