Nicole P. Anderson

Evidence of Selection for Fungicide Resistance in Zymoseptoria tritici Populations on Wheat in Western Oregon

Plant pathogens pose a major challenge to maintaining food security in many parts of the world. Where major plant pathogens are fungal, fungicide resistance can often thwart regional control efforts. Zymoseptoria tritici, causal agent of Septoria tritici blotch, is a major fungal pathogen of wheat that has evolved resistance to chemical control products in four fungicide classes in Europe. Compared with Europe, however, fungicide use has been less and studies of fungicide resistance have been infrequent in North American Z. tritici populations. Here, we confirm first reports of Z. tritici fungicide resistance evolution in western Oregon through analysis of the effects of spray applications of propiconazole and an azoxystrobin + propiconazole mixture during a single growing season. Frequencies of strobilurin-resistant isolates, quantified as proportions of G143A mutants, were significantly higher in azoxystrobin-sprayed plots compared with plots with no azoxystrobin treatment at two different locations and were significantly higher in plots of a moderately resistant cultivar than in plots of a susceptible cultivar. Thus, it appears that western Oregon Z. tritici populations have the potential to evolve levels of strobilurin resistance similar to those observed in Europe. Although the concentration of propiconazole required to reduce pathogen growth by 50% values were numerically greater for isolates collected from plots receiving propiconazole than in control plots, this effect was not significant (P > 0.05).

First report of Cocksfoot mottle virus infecting Dactylis glomerata in Oregon and the United States.

Cocksfoot mottle virus (CfMV) is a mechanically and beetle-transmitted, non-seedtransmitted sobemovirus associated with orchardgrass (Dactylis glomerata L.) stand decline in Europe, Japan, New Zealand (Mahy and Van Regenmortel 2010), and Canada (Bittman et al. 2006). Additional hosts, reported from New Zealand (Delmiglio et al. 2010), include Festuca novae-zelandiae, Lolium spp., Poa anceps, Poa cita, Chionochloa rubra, and Dichelachne crinita. To determine if the virus is present in the United States, surveys for CfMV were conducted in 2014 and 2015 in orchardgrass seed production fields in the Willamette Valley in Oregon, where most of the orchardgrass seed produced in the United States is grown. During June, in each of 2014 and 2015, 18 orchardgrass fields were selected arbitrarily. Stand age of the seed production fields ranged from 2 to 24 years. Two of the fields were sampled in both years. Four samples (each containing 4 leaves, one from each of four plants) were collected along each of four transects in an M-shape pattern from each field. All plants sampled appeared healthy. In 2014, samples were placed in separate plastic bags and in 2015 samples were placed in deep well plates (VWR, International LLC, Radnor, PA). In each year, samples were transported over ice and stored at 5°C until processed. Samples were homogenized and tested for CfMV using DAS-ELISA, with antibodies derived from an isolate of CfMV from British Columbia, Canada. In 2014 and 2015, CfMV was detected in 61% and 72% of the fields, respectively. Symptoms were not present at the time of sampling. In 2015, eight ELISA positive samples were further examined with RT-PCR. RNA was extracted with the Direct-zol RNA MiniPrep kit (Zymo Quick Links Add to favorites

Temporal Dynamics and Spatial Variation of Azoxystrobin and Propiconazole Resistance in Zymoseptoria tritici: A Hierarchical Survey of Commercial Winter Wheat Fields in the Willamette Valley, Oregon.

Fungicide resistance can cause disease control failure in agricultural systems, and is particularly concerning with Zymoseptoria tritici, the causal agent of Septoria tritici blotch of wheat. In North America, the first quinone outside inhibitor resistance in Z. tritici was discovered in the Willamette Valley of Oregon in 2012, which prompted this hierarchical survey of commercial winter wheat fields to monitor azoxystrobin- and propiconazole-resistant Z. tritici. Surveys were conducted in June 2014, January 2015, May 2015, and January 2016. The survey was organized in a hierarchical scheme: regions within the Willamette Valley, fields within the region, transects within the field, and samples within the transect. Overall, frequency of azoxystrobin-resistant isolates increased from 63 to 93% from June 2014 to January 2016. Resistance to azoxystrobin increased over time even within fields receiving no strobilurin applications. Propiconazole sensitivity varied over the course of the study but, overall, did not significantly change. Sensitivity to both fungicides showed no regional aggregation within the Willamette Valley. Greater than 80% of spatial variation in fungicide sensitivity was at the smallest hierarchical scale (within the transect) of the survey for both fungicides, and the resistance phenotypes were randomly distributed within sampled fields. Results suggest a need for a better understanding of the dynamics of fungicide resistance at the landscape level.

Spatial methods for deriving crop rotation history

Abstract Benefits of converting 11 years of remote sensing classification data into cropping history of agricultural fields included measuring lengths of rotation cycles and identifying specific sequences of intervening crops grown between final years of old grass seed stands and establishment of new ones. Spatial and non-spatial methods were complementary. Individual-year classification errors were often correctable in spreadsheet-based non-spatial analysis, whereas their presence in spatial data generally led to exclusion of fields from further analysis. Markov-model testing of non-spatial data revealed that year-to-year cropping sequences did not match average frequencies for transitions among crops grown in western Oregon, implying that rotations into new grass seed stands were influenced by growers’ desires to achieve specific objectives. Moran’s I spatial analysis of length of time between consecutive grass seed stands revealed that clustering of fields was relatively uncommon, with high and low value clusters only accounting for 7.1 and 6.2% of fields.

Detecting and correcting logically inconsistent crop rotations and other land-use sequences

ABSTRACT Converting multi-year land-use data into crop rotation history is relatively simple in the absence of classification errors, but severely compromised in their presence. Several classification errors can in theory be detected with a matrix of logically forbidden (or extremely unlikely) year-to-year land-use transitions. We categorized 730 of 3249 potential year-to-year transitions among 57 land-use classes in western Oregon as being logically permissible, with the remaining 77.5% forbidden. Applying these restrictions to eight consecutive years of land-use data revealed that an average of 26.7% of apparent year-to-year transitions among agricultural classes were illogical, in contrast to only 2.5% and 0.6% of urban development and forest transitions. The most useful correction applied to the data involved replacement of original majority-rule values (generated during prior pixel- to object-based data conversion) with second-place classification categories for fields with inconsistent land-uses identified as occurring at the beginning, middle, or ending year of multi-year sequences. This approach reduced year-to-year land-use inconsistency to 20.1% of the agricultural area. A lengthy series of additional iterations involving substitution of either majority-rule or second-place classification categories (randomized within years and counties) in cases lacking obvious ways to determine which year in pairs of years was in error in the previous iteration stabilized at 17.4% inconsistency by iteration 128. Our corrections improved the measurement of perennial crop stand ages in the complex landscape of the Pacific Northwest and similar approaches should be useful in other complex landscapes.