Resistance to Boscalid, Fluopyram and Fluxapyroxad in Blumeriella jaapii from Michigan (U.S.A.): Molecular Characterization and Assessment of Practical Resistance in Commercial Cherry Orchards.

Management of cherry leaf spot disease, caused by the fungus Blumeriella jaapii, with succinate dehydrogenase inhibitor (SDHI) fungicides has been ongoing in Michigan tart cherry orchards for the past 17 years. After boscalid-resistant B. jaapii were first isolated from commercial orchards in 2010, premixes of SDHI fungicides fluopyram or fluxapyroxad with a quinone outside inhibitor were registered in 2012. Here, we report widespread resistance to fluopyram (FluoR), fluxapyroxad (FluxR), and boscalid (BoscR) in commercial orchard populations of B. jaapii in Michigan from surveys conducted between 2016 and 2019. A total of 26% of 1610 isolates from the 2016-2017 surveys exhibited the fully-resistant BoscR FluoR FluxR phenotype and only 7% were sensitive to all three SDHIs. Practical resistance to fluopyram and fluxapyroxad was detected in 29 of 35 and 14 of 35 commercial tart cherry orchards, respectively, in surveys conducted in 2018 and 2019. Sequencing of the SdhB, SdhC, and SdhD target genes from 22 isolates with varying resistance phenotypes showed that BoscS FluoR FluxS isolates harbored either an I262V substitution in SdhB or an S84L substitution in SdhC. BoscR FluoR FluxR isolates harbored an N86S substitution in SdhC, or contained the N86S substitution with the additional I262V substitution in SdhB. One BoscR FluoR FluxR isolate contained both the I262V substitution in SdhB and the S84L substitution in SdhC. These mutational analyses suggest that BoscR FluoR FluxR isolates evolved from fully sensitive BoscS, FluoS, FluxS isolates in the population and not from boscalid-resistant isolates that were prevalent in the 2010-2012 time period.

Survey and Genetic Analysis of Demethylation Inhibitor Fungicide Resistance in Monilinia fructicola From Michigan Orchards.

Resistance to sterol demethylation inhibitor (DMI) fungicides in Monilinia fructicola, causal agent of brown rot of stone fruit, has been reported in the southeastern and eastern United States and in Brazil. DMI resistance of some M. fructicola isolates, in particular those recovered from the southeastern United States, is associated with a sequence element termed "Mona" that causes overexpression of the cytochrome demethylase target gene MfCYP51. In this study, we conducted statewide surveys of Michigan stone fruit orchards from 2009 to 2011 and in 2019, and we determined the sensitivity to propiconazole of a total of 813 isolates of M. fructicola. A total of 80.7% of Michigan isolates were characterized as resistant to propiconazole by relative growth assays, but the Mona insert was not uniformly detected and was present in some isolates that were not characterized as DMI resistant. Gene expression assays indicated that elevated expression of MfCYP51 was only weakly correlated with DMI resistance in M. fructicola isolates from Michigan, and there was no obvious correlation between the presence of the Mona element and elevated expression of MfCYP51. However, sequence analysis of MfCYP51 from 25 DMI-resistant isolates did not reveal any point mutations that could be correlated with resistance. Amplification and sequencing upstream of MfCYP51 resulted in detection of DNA insertions in a wide range of isolates typed by DMI phenotype and the presence of Mona or other unique sequences. The function of these unique sequences or their presence upstream of MfCYP51 cannot be correlated to a DMI-resistant genotype at this time. Our results indicate that DMI resistance was established in Michigan populations of M. fructicola by 2009 to 2011, and that relative resistance levels have continued to increase to the point that practical resistance is present in most orchards. In addition, the presence of the Mona insert is not a marker for identifying DMI-resistant isolates of M. fructicola in Michigan.

Mismatched outcomes for biodiversity and ecosystem services: testing the responses of crop pollinators and wild bee biodiversity to habitat enhancement.

Supporting ecosystem services and conserving biodiversity may be compatible goals, but there is concern that service-focused interventions mostly benefit a few common species. We use a spatially replicated, multiyear experiment in four agricultural settings to test if enhancing habitat adjacent to crops increases wild bee diversity and abundance on and off crops. We found that enhanced field edges harbored more taxonomically and functionally abundant, diverse, and compositionally different bee communities compared to control edges. Enhancements did not increase the abundance or diversity of bees visiting crops, indicating that the supply of pollination services was unchanged following enhancement. We find that actions to promote crop pollination improve multiple dimensions of biodiversity, underscoring their conservation value, but these benefits may not be spilling over to crops. More work is needed to identify the conditions that promote effective co-management of biodiversity and ecosystem services.

Boscalid Resistance in Blumeriella jaapii: Distribution, Effect on Field Efficacy, and Molecular Characterization.

Cherry leaf spot (CLS), caused by the fungus Blumeriella jaapii, is a major disease of tart cherry (Prunus cerasus L.) trees, leading to early defoliation that results in uneven ripening and poor fruit quality in the current season, reduced fruit set in the following season, and increased potential for winter injury and tree death. Pristine (BASF Corporation, Research Triangle Park, NC), a commonly used fungicide for CLS management in Michigan, is a premix of boscalid, a succinate dehydrogenase inhibitor, and pyraclostrobin, a quinone outside inhibitor. Reduced efficacy of Pristine for CLS control was observed in field trials and commercial orchards and highlights the importance of fungicide resistance monitoring. A total of 1,189 isolates from 31 commercial orchards in Michigan, 111 isolates from nontreated trees (four locations in Michigan and two locations in Ohio), and 133 isolates from a research orchard were collected during 2010, 2011, and 2012 and assayed on boscalid-amended media at concentrations ranging from 0 to 25 µg ml-1. Because of the very slow growth rate of B. jaapii in culture, we determined the minimum inhibitory concentration (MIC) of boscalid as opposed to the effective concentration that inhibits mycelial growth to 50% of the control. Isolates from nontreated trees had MIC values ranging from 0.1 to 0.5 µg ml-1; the MIC of isolates from commercial orchards ranged from 0.1 to >25 µg ml-1, and isolates from the research orchard ranged from 2.5 to >25 µg ml-1. Isolates with MIC values ≥25 µg ml-1 were considered boscalid resistant and comprised 0% of the nontreated isolates, 30.4% of the commercial isolates, and 42.1% of the research orchard isolates. Sequencing of the sdhB gene of resistant isolates led to the detection of the amino acid mutation H260R, which is known to confer boscalid resistance in other phytopathogenic fungi. Our results indicate that the occurrence of the H260R mutation in Michigan populations of B. jaapii is correlated with the reduction in sensitivity to boscalid observed in commercial orchards.

Does Passive Sampling Accurately Reflect the Bee (Apoidea: Anthophila) Communities Pollinating Apple and Sour Cherry Orchards?

During bloom of spring orchard crops, bees are the primary providers of pollination service. Monitoring these insects for research projects is often done by timed observations or by direct aerial netting, but there has been increasing interest in blue vane traps as an efficient passive approach to collecting bees. Over multiple spring seasons in Michigan and Pennsylvania, orchards were monitored for wild bees using timed netting from crop flowers and blue vane traps. This revealed a distinctly different community of wild bees captured using the two methods, suggesting that blue vane traps can complement but cannot replace direct aerial netting. The bee community in blue vane traps was generally composed of nonpollinating species, which can be of interest for broader biodiversity studies. In particular, blue vane traps caught Eucera atriventris (Smith), Eucera hamata (Bradley), Bombus fervidus (F.), and Agapostemon virescens (F.) that were never collected from the orchard crop flowers during the study period. Captures of bee species in nets was generally stable across the 3 yr, whereas we observed significant declines in the abundance of Lasioglossum pilosum (Smith) and Eucera spp. trapped using blue vane traps during the project, suggesting local overtrapping of reproductive individuals. We conclude that blue vane traps are a useful tool for expanding insights into bee communities within orchard crop systems, but they should be used with great caution to avoid local extirpation of these important insects.

Evaluation of dodine, fluopyram and penthiopyrad for the management of leaf spot and powdery mildew of tart cherry, and fungicide sensitivity screening of Michigan populations of Blumeriella jaapii.

BACKGROUND: Field trials were conducted on the tart cherry cultivar Montmorency to evaluate the efficacy of dodine and the succinate dehydrogenase inhibitor (SDHI) fungicides fluopyram and penthiopyrad for control of cherry leaf spot (CLS) and powdery mildew (PM). The in vitro sensitivity of Blumeriella jaapii (CLS) to the same fungicides was also tested. RESULTS: Treatments with dodine or fluopyram were among the most effective for controlling CLS, while fluopyram or penthiopyrad treatments were among the most effective for controlling PM. In vitro studies detected a wide range of minimum inhibitory concentrations (MICs) among the isolates (0.05-400 µg AI mL(-1) ) in response to dodine. Orchard isolates showed reduced sensitivity to dodine as compared with baseline isolates. B. jaapii was more sensitive to fluopyram (0.01-10.0 µg AI mL(-1) ) than to penthiopyrad (0.01-25 µg AI mL(-1) ), and orchard isolates also showed a shift towards reduced sensitivity. CONCLUSION: The results indicate that dodine remains effective in CLS control. In addition, as penthiopyrad and fluopyram become available to growers, this research establishes baseline information that will be important for future monitoring and analysis of B. jaapii population responses to exposure to dodine and these SDHI fungicides.

How the use of chlorothalonil on golf courses impacts Paenibacillus sp., a pathogen of Ataenius spretulus (Coleoptera: Scarabaeidae).

One of the most frequently used fungicides on golf courses, chlorothalonil, was applied to field plots at four different golf courses to determine how Ataenius spretulus Haldeman, Aphodius granarius L., carabids, staphylinids, formicids and Paenibacillus sp. were affected. Chlorothalonil had no influence on the incidence of Paenibacillus sp. infection of A. spretulus larvae in golf course fairways. The incidence of Paenibacillus sp. infection of A. spretulus larvae was much greater in the rough (47.4%) compared with the fairway (26.4%) at Cattails Golf Club despite a more dense population (fourfold) of larvae in the fairway. Chlorothalonil treatment of turf plots had no influence on the number of staphylinids, carabids, formicids, or A. spretulus adults caught in pitfall traps. It also did not affect the density of A. spretulus larvae. Data from this study suggest that the widespread use of chlorothalonil on fairways is not likely to cause outbreaks of A. spretulus on golf courses.