First Report of Ascochyta Blight of Vicia hirsuta (Hairy Tare) in the Republic of Georgia Caused by Ascochyta sp
Authors: Chilvers M. I. , Horton T. L. , Peever T. L. , Kaiser W. J. , Muehlbauer F. J. 
Published: May 2007

Tan lesions with dark margins containing concentric rings of black pycnidia were observed on leaves and pods of hairy tare (Vicia hirsuta L.) growing near Ateni, GA (41°54.631′N, 44°05.586′E, elev. 730 m) on 1 July 2004. Lesions were reminiscent of those induced by Ascochyta rabiei (Pass.) Labrousse on chickpea (Cicer arietinum L.). At the time of collection, necrotic lesions were observed on the stems, leaflets, and pods of several plants. The fungus was isolated by surface-disinfecting small pieces of infected tissue in 95% EtOH for 10 s, 1% NaOCl for 1 min, and then deionized H20 for 1 min. 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 made by streaking cirrhi on 3% WA and picking germinated single conidia. After 14 days of growth, the isolated fungus had colony morphology similar to that of A. rabiei on V8 juice agar. A conidial suspension of the fungus (1 × 105 conidia/ml) was spray-inoculated onto 2-week-old plants including PI lines 628303, 628304, 420171, and 422499 of V. hirsuta and C. arietinum cv. Burpee. Plants were obtained from the USDA Western Region Plant Introduction Station, Pullman, WA, and 20 replicate plants of each genotype were inoculated. Inoculated plants were covered with a plastic cup to maintain high humidity and incubated in a growth chamber for 48 h at 18°C. Following removal of the cups, characteristic Ascochyta blight lesions were apparent 14 days after inoculation on both plant species. DNA was extracted from the isolate and 610 bp of the glyceraldehyde-3-phosphate-dehydrogenase gene (G3PD), 364 bp of the chitin synthase 1 gene, and 330 bp of the translation elongation factor 1-alpha gene were amplified with gpd-1 and gpd-2 primers (1), CHS-79 and CHS-354 primers (2), and EF1-728F and EF1-986R primers (2), respectively. Amplicons were direct sequenced on both strands and a BLAST search of the NCBI nucleotide database with consensus G3PD, CHS, and EF sequences revealed the chickpea pathogen Didymella rabiei (anamorph Ascochyta rabiei) accessions DQ383958, DQ386480, and DQ386488 as the closest matches in the databases with 95, 95, and 88% sequence similarity, respectively. These results, coupled with the morphological identification and the inoculation results, confirm the identity of the fungus as Ascochyta sp. Further research needs to be performed to determine if this represents a new species of Ascochyta. The identification of this fungus is part of a larger project to develop a phylogeny for Ascochyta spp. infecting cultivated legumes and their wild relatives that will provide a framework for the study of the evolution of host specificity and speciation of plant-pathogenic fungi. This is the second report of an Ascochyta species on V. hirsuta, and to our knowledge, the first report of Ascochyta blight of this host in the Republic of Georgia.

References: (1) M. L. Berbee et al. Mycologia 91:964, 1999. (2) I. Carbone and L. M. Kohn. Mycologia 91:553, 1999.