@article{fraser_murphy_leath_van sanford_2003, title={Effect of inoculation with selected isolates of Stagonospora nodorum on field evaluations of host resistance in winter wheat}, volume={87}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS.2003.87.10.1213}, abstractNote={ Although Stagonospora nodorum blotch occurs annually in North Carolina, selection for resistance in wheat (Triticum aestivum) breeding nurseries is hampered by the infrequent occurrence of heavy and timely disease pressure. The objective of this study was to compare estimates of host resistance in a population of 147 random winter wheat lines evaluated in epidemics produced by natural infection versus epidemics supplemented by inoculation with selected isolates. Two isolates were chosen from a set of 43 collected in North Carolina based on their aggressiveness on four wheat cultivars in a controlled environment test. Field experiments utilized a split-plot design with three replications. The main plots were inoculation treatments and the subplots were the 147 wheat genotypes. The inoculation treatments were (i) selected isolate A (more aggressive) alone, (ii) selected isolate B (less aggressive) alone, (iii) a combination of isolates A plus B, and (iv) natural infection. Selected isolate treatments were applied at Feekes growth stage 9 to 10.1, and disease intensity was measured two or three times at 14-day intervals postinoculation. The study was conducted at one location in the 1996-97 season and two locations in the 1997-98 season. High levels of natural infection occurred, and no differences were observed among the four inoculation treatments for mean disease intensity in any of the three environments. Within environments, genotype-by-inoculation treatment variance was significant in the two environments inoculated with selected isolates at growth stage 9 but not in the environment inoculated at growth stage 10.1. Magnitudes of genetic variation and heritability for Stagonospora nodorum blotch resistance were not consistently associated with main plot treatments, and inoculation with selected isolates masked genetic variation for resistance in two treatments in one environment. Genotype rank correlations for Stagonospora nodorum blotch resistance between inoculation treatments varied from zero to 0.69 within environments, but only a single correlation between inoculation treatments in different environments was observed. Estimates of host resistance in epidemics supplemented with selected isolates did not consistently agree with estimates in epidemics produced by natural infection. Our results did not support the routine use of supplemental inoculation of wheat breeding nurseries with selected isolates of S. nodorum as a means of increasing genetic gain for host resistance. }, number={10}, journal={PLANT DISEASE}, author={Fraser, DE and Murphy, JP and Leath, S and Van Sanford, DA}, year={2003}, month={Oct}, pages={1213–1220} }
 @article{fraser_shoemaker_ristaino_1999, title={Characterization of isolates of Phytophthora infestans from tomato and potato in North Carolina from 1993 to 1995}, volume={83}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS.1999.83.7.633}, abstractNote={ Eighty-five isolates of Phytophthora infestans from 33 tomato and 8 potato fields in North Carolina, South Carolina, and Tennessee were collected from 1993 to 1995 and tested for mating type, sensitivity to metalaxyl, and allozyme genotype at glucose-6-phosphate isomerase (Gpi) and peptidase (Pep) loci. One isolate collected from potato in eastern North Carolina in 1994 was the A1 mating type, whereas all other isolates from potato and tomato were the A2 mating type. Six isolates were sensitive to metalaxyl (<40% growth at 1.0 μg of metalaxyl per ml), nineteen isolates were intermediate in sensitivity to metalaxyl (>40% growth at 1.0 μg of metalaxyl per ml and <40% growth at 100 μg of metalaxyl per ml), and sixty isolates were resistant to metalaxyl (<40% growth at 1.0 and 100 μg of metalaxyl per ml). Four different allozyme genotypes at the Gpi and Pep loci were identified. The single A1 isolate found on potato in eastern North Carolina had the dilocus allozyme genotype Gpi 86/100, Pep 92/100 and was identified as the US-1 genotype. Fifty-five isolates had the dilocus allozyme genotype Gpi 100/111, Pep 100/100 and were classified as the US-7 genotype, whereas twenty-four isolates were Gpi 100/111/122, Pep 100/100 and were classified as the US-8 genotype. Two isolates that were sensitive to meta-laxyl and seventeen isolates that were intermediate in sensitivity to metalaxyl were found among the US-7 and US-8 genotypes. In addition, five isolates had the allozyme genotype Gpi 100/100, Pep 92/100 (similar to the previously reported US-6 genotype), but they were the A2 mating type and either sensitive or intermediate in response to metalaxyl. These isolates composed a new genotype not previously reported in the United States and were designated as US-18. The US-7 genotype was more frequent on tomato in western North Carolina and the US-8 genotype was present on potato in eastern North Carolina, indicating that different inoculum sources are responsible for epidemics on the two crops in different regions of the state. }, number={7}, journal={PLANT DISEASE}, author={Fraser, DE and Shoemaker, PB and Ristaino, JB}, year={1999}, month={Jul}, pages={633–638} }