Black shank disease of tobacco, caused by the oomycete Phytophthora nicotianae, is a major threat to production in the United States and tobacco-producing areas worldwide. In a statewide survey of North Carolina, the rapid shift from race 0 to race 1 was documented. Collected pathogen isolates were characterized phenotypically for mating type and mefenoxam sensitivity, and genotypically by comparing sequences from three cytoplasmic and two nuclear regions. Both the A1 and A2 mating types were found throughout the state. When both mating types were recovered from the same field, pairings of isolates yielded viable oospores, indicating for the first time the potential for sexual sporulation by P. nicotianae in natural populations. Because the loss of complete resistance required a renewed use of the fungicide mefenoxam, a subset of the survey isolates was screened for sensitivity to the fungicide. All isolates were sensitive, with a mean effective concentration to inhibit 50% of hyphal growth of 0.4 μg/ml that was similar across mating types and races. Molecular characterization of 226 isolates revealed that the pathogen exists as multiple clonal types within the state. Genetic diversity among the pathogen population and the potential for sexual recombination may help explain the ability of the pathogen to rapidly adapt to host resistance genes.

Stevia (Stevia rebaudiana (Bertoni) Bertoni) is an emerging perennial crop in the United States. Small black root lesions were first observed on overwintering crowns dug in March 2016 from a field planting of stevia in Rocky Mount, NC. Similar root lesions were observed on first year plants in Kinston and Rocky Mount, NC throughout the 2016 growing season in fields with a history of soybean and corn rotations. Isolations from lesions were made on potato dextrose agar amended with 50 µg/ml of streptomycin sulfate and penicillin G. Isolations were incubated at room temperature (22 to 25C) for 1 week and observed for colony morphology. Grey-black colonies that became dark with age were isolated into pure culture. Hyphae were septate with barrel-shaped cells, and numerous 50-150 µm microsclerotia resembling those produced by Macrophomina (Kaur et al., 2012) were present. Pathogen identification was confirmed by sequencing the internal spacer (ITS) region of ribosomal DNA. DNA was extracted from mycelia with t...

Microscopy and stained specimens engage students visually as they learn about plant anatomy, a topic covered in many biology and introductory science courses. In this activity, students section plant material and prepare specimens to view under a brightfield microscope. Using a camera or cell phone, images of microscope slide contents allow students to label plant parts and engage in discussions with peers. The addition of scale bars to their images will allow a better understanding of the relationships of the various structures observed in the functioning of plants.

Tomato spotted wilt virus (TSWV) (genus Tospovirus, family Bunyaviridae) is an important plant pathogen on vegetables, ornamentals, and field crops across the southeast US (Abad et al. 2005). TSWV was first detected in North Carolina in 1988 in tobacco and tomato fields (Cho et al. 1995). Stevia (Stevia rebaudiana (Bertoni) Bertoni) is an emerging perennial crop in the United States, grown for 3 to 5 years with two harvests per growing season. Stevia leaves contain numerous glycosides that are extracted for use as a natural, low calorie sweetener. In current production practices, stevia plants are started from seed in a greenhouse system and transplanted to the field 8 to 10 weeks after germination. In February 2015, virus-like symptoms were observed on stevia plants in a research greenhouse in Raleigh, North Carolina. Symptomless plants were dug from the field in the fall of 2014 and moved to the greenhouse to make crosses. Symptoms began as mottling, distortion, and chlorosis of leaves and progressed to...

Septoria leaf spot (SLS) affects stevia leaves, reducing their quality. Estimates of SLS severity on different genotypes are made to identify resistance and as a basis to compare management approaches. The use of standard area diagrams (SADs) can improve the accuracy and reliability of severity estimates. In this study, we developed new SADs with six illustrations (0.5, 1, 10, 25, 40, and 75% severity). The SADs were validated by raters with and without experience in estimating SLS. Raters evaluated 40 leaf photos with SLS severities ranging from 0 to 100% without and with the SADs. Agreement (ρ_c), bias (C_b), precision (r), and intracluster correlation (ρ) coefficients were significantly closer to “true” severity values when the SADs was used by inexperienced (ρ_c = 0.89; C_b = 0.97; r = 0.90, ρ = 0.81) and experienced (ρ_c = 0.94; C_b = 0.99; r = 0.95, ρ = 0.91) raters. The SADs were tested under field conditions in Paraguay, Mexico, and the United States, with inexperienced raters assigned to two groups, one SADs trained and the other not trained, that estimated SLS severity three times: first, all raters without SADs and no time limit for the estimates; second, only the SADs-trained group used SADs and no time limit; and third, only the SADs-trained group used SADs, with a time limit of 10 s imposed per specimen assessment. Agreement and reliability of SLS severity estimates significantly improved when raters used the SADs without a time limit. The use of the new SADs improved the accuracy, precision, and reliability of SLS severity estimates, enhancing the uniformity in assessment across different stevia programs.