|HABIBI, A. - Washington State University|
|TOBIN, PEEVER - Washington State University|
|WONYONG, KIM - Washington State University|
|CHILVERS, MARTY - Michigan State University|
|Kaiser Jr, Walter|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2015
Publication Date: 9/29/2015
Citation: Habibi, A., Tobin, P., Wonyong, K., Chilvers, M., Chen, W., Kaiser Jr, W.J., Muehlbauer, F.J. 2015. First report of Ascochyta blight of Spotted Locoweed (Astragalus lentiginosus) caused by Ascochyta sp. in Idaho. Plant Disease. 99:1446.
Interpretive Summary: Fungal pathogens in the genus Ascochyta cause Ascochyta blight on many important crops, particularly legumes. Generally they have narrow host ranges, with a few exceptions infecting species of a plant genus or closely related species. Realizing the wide occurrence of Ascochyta blights on crops and wild plant species is important for diagnosing plant disease and for studying disease cycle, to develop management strategies. In this study, Ascochyta blight was identified in the wild plant species spotted locoweed (Astragalus lentiginosus) in the Pacific Northwest. Lesions were similar to those induced by Ascochyta spp. on other wild and cultivated legumes, i.e. small circular tan colored lesions with a dark margin. Fungi isolated from the diseased lesions were identified as Ascochyta sp. based on morphology and partial DNA sequences of three genes, the glyceraldehyde-3-phosphate-dehydrogenase gene, the translation elongation factor 1-alpha and chitin synthase. Inoculation onto 3-week old plants of faba bean (Vicia faba), pea (Pisum sativum), alfalfa (Medicago sativa), and spotted locoweed resulted in characteristic Ascochyta blight lesions on the original host spotted locoweed, 6 days after inoculation. A few scattered lesions were seen on faba bean and a slight yellowing of inoculated leaves was observed on pea. Alfalfa and non-inoculated A. sativa control plants displayed no visible symptoms. This is the second report of Ascochyta blight of Astragalus spp. in the US and the first report of Ascochyta blight of A. lentiginosus worldwide.
Technical Abstract: Characteristic Ascochyta blight lesions were observed on leaves and pods of spotted locoweed (Astragalus lentiginosus) growing at two sites in Twin Falls and Owyhee County, Idaho, USA in June 2005. Lesions appeared similar to those induced by Ascochyta spp. on other wild and cultivated legumes, i.e. small circular tan colored lesions with a dark margin. Fungi were isolated by surface-disinfesting small sections of infected leaf tissue. Tissue pieces were placed on 3% water agar (WA) for 24 h under fluorescent lights with a 12 h photoperiod to induce sporulation. Single conidial isolations were performed by streaking conidia on 3% WA, picking germinated conidia and culturing on V8 juice agar. Two isolated fungi had colony morphologies similar to that of other Ascochyta spp. (teleomorphs: Didymella spp.). Isolates were spray-inoculated on 3-week-old faba bean (Vicia faba L.) USDA-NPGS PI 512015, pea (Pisum sativum L.) PI 574510, alfalfa (Medicago sativa L.) PI 536535 and Astragalus lentiginosus PI W642479 (10 plants per isolate, 1 x 105 conidia/ml). Germination of A. lentiginosus seeds was facilitated by mechanical scarification. Plants were incubated at 20°C and covered with a plastic cup to maintain high humidity for 24 h. Characteristic Ascochyta blight lesions were apparent 6 days after inoculation on A. lentiginosus. A few scattered lesions were seen on V. faba and a slight yellowing of inoculated leaves was observed on P. sativum. M. sativa and non-inoculated A. sativa control plants displayed no visible symptoms. DNA was extracted from the isolates and approximately 470 bp of the glyceraldehyde-3-phosphate-dehydrogenase gene (G3PD) and 330 bp of the translation elongation factor 1-alpha (EF) and chitin synthase (CHS) genes were amplified with gpd-1/gpd-2 primers, EF1-728F/EF1-986R, and CHS-79F/CHS-354R primers, respectively. Amplicons were direct-sequenced on both strands and BLAST searches of the NCBI nucleotide database with consensus sequences were performed. The closest matches obtained for the G3PD, EF, and CHS sequences were Ascochyta sp. isolate Georgia-11 sampled from Vicia hirsuta (tiny vetch) in the Republic of Georgia with >99% similarity to GenBank accessions DQ383973, DQ386504, DQ386487, respectively. One isolate of this fungus was previously included in a phylogeny describing the teleomorph of Ascochyta pisi infecting pea. These results, coupled with the morphological identification and inoculation results confirm the identity of the fungus as Ascochyta sp. This is the second report of Ascochyta blight of Astragalus spp. in the US and the first report of Ascochyta blight of A. lentiginosus worldwide.