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Subject: resistance

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    Sensitivity of Alternaria Species to Ten Single-Site Mode of Action Fungicides
    (North Dakota State University, 2020) Rodriguez, Sarah Marie Budde
    Early blight caused by Alternaria solani and brown spot caused by the small-spored Alternaria spp., Alternaria alternata, Alternaria arborescens, and Alternaria tenuissima are observed annually in midwestern potato production areas. The use of foliar fungicides remains a primary management strategy. However, Alternaria spp. have developed reduced-sensitivity and/or resistance to many single-site fungicides such as quinone outside inhibitor (QoI), succinate dehydrogenase inhibitor (SDHI), and anilinopyrimidines (AP) fungicides in recent years. Boscalid, fluopyram, solatenol, and adepidyn are EPA-registered SDHI fungicides applied commercially to a variety of crops including potato. High intrinsic activity was observed in fluopyram, solatenol and adepidyn to A. solani isolates. Adepidyn and solatenol reduced disease severity caused by A. solani in field evaluations. Molecular characterization of 2018 A. solani field isolates determined that the frequency of the D123E and H134R SDH mutations increased. In contrast, the H278R/Y and H133R SDH mutations were found at low frequency. Adepidyn demonstrated the highest intrinsic activity against the small-spored Alternaria spp. but high intrinsic activity was also observed with boscalid, fluopyram, and solatenol. In vivo experiments demonstrated that adepidyn, solatenol, and fluopyram were more effective at managing A. arborescens and A. tenuissima than boscalid. Under greenhouse conditions, adepidyn and solatenol reduced brown spot severity caused by A. alternata to a greater extent than did fluopyram and boscalid. Results of these studies determined that accurate pathogen identification of small-spored Alternaria spp. may be important for brown spot management. Fludioxonil and cyprodinil exhibited a higher efficacy against of A. solani isolates when compared to pyrimethanil in greenhouse assays. Fludioxonil and cyprodinil were also highly efficacious against the Alternaria spp. evaluated and appear to be a good addition into fungicide rotation programs for early blight and brown spot management. Anilinopyrimidine (AP) (pyrimethanil and cyprodinil) and phenylpyrrole (PP) (fludioxonil) fungicides have demonstrated high intrinsic activity against other pathogens. Determining the efficacy of these fungicides on Alternaria spp. is important to the potato industry.
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    Molecular Characterization of Root-Lesion Nematode Species from Corn Fields in North Dakota and Evaluation of Resistance in Corn Hybrids
    (North Dakota State University, 2019) Akhter, Nasima
    The molecular characterization of Pratylenchus species determined from D2-D3 of 28S rDNA, ITS of rDNA, and COI of mtDNA regions revealed four Pratylenchus species from North Dakota, P. scribneri, P. neglectus, Pratylenchus sp. (ND-2016 isolate HG51), and Pratylenchus sp. (ND-2017). They were clustered in four separate clades in the phylogenetic trees indicating the divergence among species. P. scribneri and Pratylenchus sp. (ND-2016 isolate HG51) were closely associated and Pratylenchus sp. (DH-2017) was closely related to Pratylenchus sp. (ND-2016 isolate HG51). However, P. neglectus was not closely associated with the other three species. Moreover, resistance evaluation of ten corn hybrids to Pratylenchus scribneri, P. neglectus, and Pratylenchus sp. (ND-2017) revealed that 1392 VT2P was moderately resistant to three Pratylenchus species. PFS74K89 and 4913 VT2RIB were moderately resistant to two of the three Pratylenchus species. X5B-8801, DK 43-46, and DKC 44-13 were susceptible to two of the three Pratylenchus species.
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    Managing Soybean Cyst Nematode by Utilizing Cover Crops and Resistant Sources from Early Maturing Soybean Accessions
    (North Dakota State University, 2020) Acharya, Krishna
    Greenhouse and microplot studies were conducted for understanding the effects of cover crop species/cultivars for hosts and population reduction of soybean cyst nematode (SCN; Heterodera glycines) from the fields of North Dakota. Moreover, early-maturing soybean [Glycine max (L.)] accessions from different countries of origin were screened for resistance against two common SCN populations for finding new sources of resistance. Thirty-eight cover crop species/cultivars were evaluated for their hosting ability of two SCN populations (SCN103 and SCN2W) from two fields of North Dakota in greenhouse experiments. The majority of the tested crops were non-hosts for both SCN populations. However, a few of them, such as Austrian winter pea (Pisum sativum L.), crimson clover (Trifolium incarnatum L. cv. Dixie), crambe (Crambe abyssinica, cv. BelAnn), field pea, cvs. Aragorn and Cooper, hairy vetch (Vicia villosa Roth), turnip (Brassica rapa L. cv. Purple top), and white lupine (Lupinus albus L.) were poor-hosts/hosts of both SCN populations. Furthermore, thirteen of them were tested for the SCN population reduction either or both in the greenhouse and microplot experiments. Out of 13, at least four crops, such as annual ryegrass (Lolium multiflorum L.), brown mustard (Brassica juncea L. cv. Kodiak), daikon radish (Raphanus sativus L.), and turnip cv. Pointer showed more than 50% population reduction compared with initial population densitiy, consistently in the greenhouse or microplot experiments. The resistance screening of 152 early-maturing soybean accessions showed that a majority of the accessions were susceptible/moderately susceptible to both SCN populations (SCN HG type 0 and 2.5.7), while a few (n=18) showed good resistance responses to both or either of the SCN populations. The cover crops, which were non-hosts/poor-hosts and have a greater ability for the SCN population reduction have great potential to be included in an integrated SCN management strategy. The novel resistant accessions identified in this study have the potential to be used in soybean breeding for developing SCN-resistant cultivars after confirming their resistance response and identifying the resistance genes/loci. The results obtained from this study helps in developing a sustainable SCN management strategy in the northern Great Plains.
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    Horseweed (Erigeron canadensis) Control in No-Till Soybean Systems on a Coarse Textured Soil
    (North Dakota State University, 2020) Froemke, Aaron Michael
    Horseweed (Erigeron canadensis) is a competitive winter or summer annual broadleaf weed. When uncontrolled, horseweed can reduce soybean (Glycine max) yields by 93%. Research was conducted to advance our knowledge on horseweed growth stage response to foliar-active and residual herbicides, fall applications, and the utility of differing herbicide technologies. Greenhouse results determined that herbicide efficacy was greatest when applied to early rosette horseweed providing an average control of 70% across herbicide treatments. Field trials determined that preventing new emergence with flumioxazin, added with dicamba or paraquat to kill existing plants in the fall, increased control to 99% the following spring. Field trials also determined that dicamba, applied PRE or POST, provided excellent horseweed control and was an effective soybean technology system for horseweed-infested fields. Saflufenacil controlled existing plants, but residual benefits were unclear. Further research must be done to investigate residual activity of PRE herbicides applied before horseweed emergence.