East Lansing, MI, United States
East Lansing, MI, United States

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Habibi1 A.,Washington State University | Peever T.L.,Washington State University | Kim W.,Washington State University | Chilvers M.I.,Soil and Microbial science | And 3 more authors.
Plant Disease | Year: 2015

Characteristic Ascochyta blight lesions were observed on leaves and pods of spotted locoweed (Astragalus lentiginosus) growing at two sites in Twin Falls and Owyhee counties, Idaho, USA in June 2005. Site characteristics were 42.41746° N, 114.30218° W (elevation 1289 m) and 42.08173° N, 115.12820° W (elevation 1726 m), respectively. Lesions appeared similar to those induced by Ascochyta spp. on other wild and cultivated legumes, i.e., small, circular, tan lesions with a dark margin. Fungi were isolated by surface-disinfesting 3-mm × 3-mm sections of infected leaf tissue in 95% EtOH for 10 s, 1% NaOCl for 1 min, then deionized H2O 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 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. (syn. Didymella spp.). Isolates were spray-inoculated on 3-week-old faba bean (Vicia faba L.) USDA-NPGS Plant Introduction No. 512015, pea (Pisum sativum L.) PI 574510, alfalfa (Medicago sativa L.) PI 536535, and Astragalus lentiginosus PI W642479 (10 plants per isolate, 1 × 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 noninoculated 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 (Berbee et al. 1999), and EF1-728F/EF1-986R and CHS-79F/CHS-354R primers (Carbone and Kohn, 1999), 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, and DQ386487, respectively. One isolate of this fungus was previously included in a phylogeny describing the teleomorph ofAscochyta pisi infecting pea (Chilvers et al. 2009). 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 United States and the first report of Ascochyta blight of A. lentiginosus worldwide. © 2015 The American Phytopathological Society.

Miklas P.N.,U.S. Department of Agriculture | Porter L.D.,U.S. Department of Agriculture | Kelly J.D.,Soil and Microbial science | Myers J.R.,Oregon State University
European Journal of Plant Pathology | Year: 2013

White mold, caused by Sclerotinia sclerotiorum, is a devastating fungal disease of common bean (Phaseolus vulgaris L.) worldwide. Physiological resistance and disease avoidance conferred by plant architecture-related traits contribute to white mold field resistance. Our objective was to further examine white mold disease avoidance in common bean. A comparative map composed of 79 quantitative trait loci (QTL) for white mold resistance (27), disease avoidance traits (36) and root traits (16) was generated. Thirteen white mold resistance QTL, six with strong and seven with weak associations with disease avoidance traits, were observed. Root length and lodging QTL co-located in three regions. Canopy porosity and height, and lodging were highly correlated with disease severity score in field screening trials conducted from 2000 to 2011. Resistance to lodging was extremely important for reducing disease severity in both dry and snap bean (r = 0. 61 across 11 trials). Avoidance traits were less effective in reducing disease severity in trials with heavy disease pressure. Dry bean lines with physiological resistance in combination with disease avoidance traits did not require fungicide application to protect yield potential under moderate and heavy disease pressure. Given the complexity of disease resistance as evidenced by the comparative QTL map, marker-assisted breeding for disease avoidance is not recommended at this time. Instead, selecting for resistance to white mold in the field, in combination with high yield potential and acceptable maturity, is the recommended strategy for improving both disease avoidance and physiological resistance to white mold in cultivars with commercially acceptable agronomic traits. © 2013 US Government.

Kravchenko A.,Soil and Microbial science | Chun H.-C.,Soil and Microbial science | Mazer M.,Soil and Microbial science | Wang W.,Soil and Microbial science | And 3 more authors.
Applied Soil Ecology | Year: 2013

The study evaluated the effects of soil intra-aggregate pore distributions on movement and fate of E. coli (a global indicator of fecal pollution) within soil aggregates. The first objective was to characterize pore structure of intact soil aggregates (4-6. mm in size) using X-ray computed microtomography and to quantify the differences in pore structures of the aggregates from the same soil type but under >18 year contrasting land use and management settings. The studied settings were (i) conventionally plowed row crop (CT), (ii) no-till row crop (NT), and (iii) native succession vegetation (NS) treatments from Long Term Ecological Research site, W.K. Kellogg Biological Station, southwest Michigan. The second objective was to examine spatial distribution of E. coli introduced into the aggregates and the relationships between E. coli distributions and intra-aggregate pores. The results indicated that E. coli distribution in the aggregates was driven by specific configurations of the intra-aggregate pores. When the aggregates' initial water contents were relatively low, presence of large (>100 μm) pores in the aggregate interiors limited water and thus E. coli entry. Such centrally located large pores were more abundant in the aggregates from NT and NS treatments as compared to CT aggregates. Medium-sized pores (30-60 μm) were more abundant in the aggregates from CT soil and such pores were relatively homogeneously distributed through entire bodies of CT aggregates. Thus, upon entering the aggregate, E. coli became more uniformly distributed through the CT aggregates, while in NT and NS aggregates it more commonly remained in the aggregate exterior parts without reaching the interiors. Implications of these distributional patterns for E. coli survival and re-entering water flow in soil under different land use need to be addressed in further studies. © 2012 Elsevier B.V.

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