Fungicide Sensitivity of Phytophthora Isolates from the Washington Red Raspberry Industry.

Phytophthora rubi is an important pathogen causing Phytophthora root rot of red raspberries worldwide. Management of this disease is partially achieved with fungicides, but efficacy has been low, and growers are concerned about fungicide resistance. To determine whether fungicide resistance is developing, Phytophthora species were isolated from 26 raspberry fields with root rot, identified, and evaluated for sensitivity to four fungicides: mefenoxam, phosphorous acid, oxathiapiprolin, and dimethomorph. The majority of the recovered 152 Phytophthora isolates were P. rubi (143 isolates, 25 fields), with P. megasperma (8 isolates, 2 fields) and P. gonapodyides (1isolate, 1field) being found much less frequently. These results confirm P. rubi as the dominant species affecting the Washington red raspberry industry. Almost all tested isolates were sensitive to all four fungicide chemistries, although three isolates were less sensitive to mefenoxam, with effective concentration for 50% growth inhibition (EC50) values ranging from 3.53 to 100 µg active ingredient/ml. No resistance was detected against current fungicide label rates. However, other reasons were identified for why fungicides have been ineffective. Label rates vary widely by brand, and most fungicides are applied in the fall when P. rubi is inactive. In addition, some phosphorous acid products are only labeled for foliar applications, which have been shown to be less effective than soil applications in other agricultural systems. Efficacy trials are needed to compare foliar and soil fungicide applications at different times of the year for their ability to control Phytophthora root rot in red raspberry production fields.

Arbuscular mycorrhizae influence raspberry growth and soil fertility under conventional and organic fertilization.

Introduction: Introducing beneficial soil biota such as arbuscular mycorrhizal fungi (AMF) to agricultural systems may improve plant performance and soil fertility. However, whether bioinocula species composition affects plant growth and soil fertility, and whether fertilizer source influences AMF colonization have not been well characterized. The objectives of this research were to: (1) assess if AMF bioinocula of different species compositions improve raspberry (Rubus idaeus L.) performance and characteristics of soil fertility and (2) evaluate the impact of fertilizer source on AMF colonization. Methods: Five bioinocula with different AMF species compositions and three fertilizer sources were applied to tissue culture raspberry transplants in a randomized complete block design with eight replicates. Plants were grown in a greenhouse for 14 weeks and plant growth, tissue nutrient concentrations, soil fertility, and AMF root colonization were measured. Results: Shoot K and Zn concentrations as well as soil pH and K concentration increased in the Commercial Mix 1 treatment (Glomus, Gigaspora, and Paraglomus AMF species) compared to the non-inoculated control. RFI (raspberry field bioinoculum; uncharacterized AMF and other microbiota) increased soil organic matter (SOM), estimated nitrogen release (ENR), and soil copper (Cu) concentration compared to the non-inoculated control. Furthermore, plants receiving the Mix 1 or RFI treatments, which include more AMF species, had greater AMF root colonization than the remaining treatments. Plants receiving organic fertilizer had significantly greater AMF colonization than conventionally fertilized plants. Conclusion: Taken together, our data indicate that coupling organic fertilizers and bioinocula that include diverse AMF species may enhance raspberry growth and soil fertility.

Physical characteristics of soil-biodegradable and nonbiodegradable plastic mulches impact conidial splash dispersal of Botrytis cinerea.

Botrytis cinerea causes gray mold disease of strawberry (Fragaria ×ananassa) and is a globally important pathogen that causes fruit rot both in the field and after harvest. Commercial strawberry production involves the use of plastic mulches made from non-degradable polyethylene (PE), with weedmat made from woven PE and soil-biodegradable plastic mulch (BDM) as emerging mulch technologies that may enhance sustainable production. Little is known regarding how these plastic mulches impact splash dispersal of B. cinerea conidia. The objective of this study was to investigate splash dispersal dynamics of B. cinerea when exposed to various plastic mulch surfaces. Mulch surface physical characteristics and conidial splash dispersal patterns were evaluated for the three mulches. Micrographs revealed different surface characteristics that have the potential to influence splash dispersal: PE had a flat, smooth surface, whereas weedmat had large ridges and BDM had an embossed surface. Both PE mulch and BDM were impermeable to water whereas weedmat was semi-permeable. Results generated using an enclosed rain simulator system showed that as the horizontal distance from the inoculum source increased, the number of splash dispersed B. cinerea conidia captured per plate decreased for all mulch treatments. More than 50% and approximately 80% of the total number of dispersed conidia were found on plates 10 and 16 cm away from the inoculum source across all treatments, respectively. A significant correlation between the total and germinated conidia on plates across all mulch treatments was detected (P<0.01). Irrespective of distance from the inoculum source, embossed BDM facilitated higher total and germinated splashed conidia (P<0.001) compared to PE mulch and weedmat (P = 0.43 and P = 0.23, respectively), indicating BDM's or embossed film's potential for enhancing B. cinerea inoculum availability in strawberry production under plasticulture. However, differences in conidial concentrations observed among treatments were low and may not be pathologically relevant.

Microbial Load of Fresh Blueberries Harvested by Different Methods.

Currently, more and more growers are transitioning to the use of over-the-row machine harvesters for harvesting fresh market blueberries. This study assessed the microbial load of fresh blueberries harvested by different methods. Samples (n = 336) of 'Draper' and 'Liberty' northern highbush blueberries, which were harvested using a conventional over-the-row machine harvester, a modified machine harvester prototype, ungloved but sanitized hands, and hands wearing sterile gloves were collected from a blueberry farm near Lynden, WA, in the Pacific Northwest at 9 am, 12 noon, and 3 pm on four different harvest days during the 2019 harvest season. Eight replicates of each sample were collected at each sampling point and evaluated for the populations of total aerobes (TA), total yeasts and molds (YM), and total coliforms (TC), as well as for the incidence of fecal coliforms and enterococci. The harvest method was a significant factor (p < 0.05) influencing the TA and TC counts, the harvest time was a significant factor influencing the YM counts, while the blueberry cultivar was an insignificant (p > 0.05) factor for all three indicator microorganisms. These results suggest that effective harvester cleaning methods should be developed to prevent fresh blueberry contamination by microorganisms. This research will likely benefit blueberry and other fresh fruit producers.

Leaf Tissue Macronutrient Standards for Northern Highbush Blueberry Grown in Contrasting Environments.

Leaf tissue testing is a useful tool for monitoring nutrient requirements in northern highbush blueberry (Vaccinium corymbosum L.; abbreviated as "blueberry") but may require adaptation to specific growing environments. The objective of this study was to evaluate macronutrient concentrations in early-, mid-, and late-season blueberry cultivars grown in two contrasting environments, specifically eastern and western Washington. Climate and soil conditions between these two regions differ tremendously with eastern Washington being more arid with naturally calcareous soils lower in soil organic matter. Sampling was conducted over a 3-year period in commercial fields. Leaf tissue nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) concentrations were affected by year (Y), growing region (R), cultivar (C), and Day of Year (DOY) that the samples were collected with many interactions. Leaf nutrient concentrations were higher, on average, in western than eastern Washington except for Ca and Mg, indicating sufficiency levels should differ between these regions. Leaf macronutrients generally stabilized between DOY 212-243 (1-31 August), suggesting this period is optimal for tissue sampling. Findings from this study demonstrate the importance of considering regional effects and may be applicable for blueberry cultivated in similar pedo-climactic conditions around the world.

Evaluation of real-time nutrient analysis of fertilized raspberry using petiole sap.

The time delay in receiving conventional tissue nutrient analysis results caused red raspberry (Rubus idaeus L.) growers to be interested in rapid sap tests to provide real-time results to guide immediate nutrient management practices. However, sap analysis has never been conducted in raspberry. The present work aimed to evaluate the relationship of petiole sap nitrate (NO3 -), potassium (K+), and calcium (Ca2+) concentrations measured using compact ion meters and leaf tissue total nitrogen (TN), potassium (K), and calcium (Ca) concentrations measured using conventional tissue nutrient analysis. The relationship of petiole sap NO3 - and leaf tissue TN concentrations with plant growth and production variables was also explored. Fertilizer treatments of urea were surface applied to raised beds of established "Meeker" floricane red raspberry plots at control, low, medium, and high rates (0, 34, 67, and 101 kg N ha-1, respectively) in 2019 and 2020. The experiment was arranged in a randomized complete block design with three replications. Whole leaves were collected from representative primocanes in mid- and late- July and August 2019 and 2020 (i.e., four sampling time points per year). At each sampling time point, a subsample of leaves was used for petiole sap analyses of NO3 -, K+, and Ca2+ concentrations using compact ion meters, and conventional tissue testing of leaf tissue TN, K, and Ca concentrations, respectively. There were no interactions between N fertilizer rate and year nor between N fertilizer rate and sampling time. No significant differences were found due to N fertilizer rate for petiole sap NO3 -, K+, Ca2+ nor leaf tissue TN, K, Ca concentrations. However, significant year and sampling time effects occurred in measured petiole sap and leaf tissue nutrient concentrations. Overall, the correlations between petiole sap NO3 - and leaf tissue TN, petiole sap Ca2+ and leaf tissue Ca, petiole sap K+ and leaf tissue K concentrations were non-strong and inconsistent. Future research is warranted as the interpretation of correlations between raspberry petiole sap and leaf tissue nutrient concentrations were inconclusive.

Development of a Decision Support System for the Management of Mummy Berry Disease in Northwestern Washington.

Mummy berry, caused by Monilinia vaccinii-corymbosi, is the most important disease of the northern highbush blueberry (Vaccinium corymbosum L.) in North America and can cause up to 70% yield losses in affected fields. A key event in the mummy berry disease cycle is the primary infection phase where ascospores are released by apothecia that infect emerging floral and vegetative tissues. Current management of mummy berry disease in northwestern Washington is predominantly reliant on the prevention of primary infections through prophylactic, calendar-based fungicide spray applications early in the growing season. To improve the understanding of risk during these periods and to help tailor management strategies, we developed a decision support system (DSS) based on field records spanning over five seasons and four locations in northwestern Washington. Environmental conditions across the region were highly uniform but different dynamics of apothecial development were observed under high- and low-management regimes. Based on our analysis, we suggest basing the initial iteration of the DSS on two sub-models. The first sub-model predicts the onset of apothecia based on chill-unit accumulation under high- and low-management regimes, and the second predicts primary infection risk, which provides opportunities to improve the timing of fungicide applications. The synoptic DSS proposed here is based on the current biological knowledge of the pathosystem and available data for the northwestern Washington region. We provide the analysis and the DSS implementation and evaluation as an open-source repository, providing opportunities for further improvements. Finally, we provide suggestions for future research and the operational efforts needed for improving the utility and accuracy of the mummy berry DSS.

There and back again; historical perspective and future directions for Vaccinium breeding and research studies.

The genus Vaccinium L. (Ericaceae) contains a wide diversity of culturally and economically important berry crop species. Consumer demand and scientific research in blueberry (Vaccinium spp.) and cranberry (Vaccinium macrocarpon) have increased worldwide over the crops' relatively short domestication history (~100 years). Other species, including bilberry (Vaccinium myrtillus), lingonberry (Vaccinium vitis-idaea), and ohelo berry (Vaccinium reticulatum) are largely still harvested from the wild but with crop improvement efforts underway. Here, we present a review article on these Vaccinium berry crops on topics that span taxonomy to genetics and genomics to breeding. We highlight the accomplishments made thus far for each of these crops, along their journey from the wild, and propose research areas and questions that will require investments by the community over the coming decades to guide future crop improvement efforts. New tools and resources are needed to underpin the development of superior cultivars that are not only more resilient to various environmental stresses and higher yielding, but also produce fruit that continue to meet a variety of consumer preferences, including fruit quality and health related traits.

Micrographic View of Graft Union Formation Between Watermelon Scion and Squash Rootstock.

Grafting has become a common practice for watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] production in many parts of the world, due to its efficacy against biotic and abiotic stressors. However, grafting success for watermelon is challenging in part due to the complex anatomy of the cucurbit vascular system. The survival of grafted transplants depends on compatibility between the scion and rootstock, which in turn depends on anatomical, physiological, and genetic variables. A better understanding of cucurbit anatomy and graft union formation would inform grafting approaches and transplant management. An anatomical study was conducted by scanning electron microscopy (SEM) at 11 and 25 days after grafting (DAG) with seedless watermelon cultivar 'Secretariat' grafted onto compatible rootstock cultivars 'Pelop' (Lagenaria siceraria) and 'Tetsukabuto' (Cucurbita maxima × Cucurbita moschata) in comparison to non-grafted watermelon and rootstock seedlings. At 11 DAG, the parenchymatic cells of the central pith of grafted plants were dead and a necrotic layer was observed, representing the beginning of callus formation. New xylem strands were formed in the vascular system, connecting the rootstock with the scion. At 25 DAG, fully developed vascular bundles at the graft interface were observed with both scion-rootstock combinations. Although more studies are necessary to characterize the sequence of physiological events after grafting in Cucurbit species, this is one of the first studies to describe the complex anatomical changes that occur during watermelon graft healing.

Honey bee (Apis mellifera) colony strength and its effects on pollination and yield in highbush blueberries (Vaccinium corymbosum).

Many pollination studies with honey bees have examined the effect of colony density on crop yield and yet overlook the effect of variation in the population size of these colonies. High colony density in northern highbush blueberry has been met with concerns from beekeepers who feel higher densities will intensify outbreaks of European foulbrood (EFB, Melissococcus plutonius, Truper and dé Clari), a honey bee brood disease. The purpose of this study was to confirm the prevalence of EFB in colonies pollinating blueberries and to determine whether field-level variation in the population of adult workers in colonies explained variation in blueberry fruit set and/or yield. We addressed these objectives over the course of two production seasons at 13 commercial blueberry fields in Oregon, USA, stocked with identical densities of 10 colonies/ha. We confirmed that all colonies had negligible symptoms of EFB at the start of blueberry pollination, but 53% of colonies in 2019 and 41% in 2020 had symptoms immediately following the pollination season. We also validated a method for rapidly assessing adult honey bee colony populations, namely by counting the rate of foragers returning to colonies, and it was found to be strongly correlated to true internal adult bee population independent of year and ambient temperature at the time of evaluation. Using returning forager counts, we determined there was considerable variation in the average population of colonies at each field, ranging from an estimated 10,300 to 30,700 adult worker bees per colony. While average colony strength did not predict variation in fruit set, it was related to variation in yield, independent of year. Our linear model of flight count (as a proxy for colony strength) predicts estimated yield increases of up to 25,000 kg/ha of blueberries could be achieved by colonies stronger than the recommended six frame minimum, suggesting that higher pollination benefits could be achieved without increasing hive density if stronger colonies are promoted.

15 years of GDR: New data and functionality in the Genome Database for Rosaceae.

The Genome Database for Rosaceae (GDR, https://www.rosaceae.org) is an integrated web-based community database resource providing access to publicly available genomics, genetics and breeding data and data-mining tools to facilitate basic, translational and applied research in Rosaceae. The volume of data in GDR has increased greatly over the last 5 years. The GDR now houses multiple versions of whole genome assembly and annotation data from 14 species, made available by recent advances in sequencing technology. Annotated and searchable reference transcriptomes, RefTrans, combining peer-reviewed published RNA-Seq as well as EST datasets, are newly available for major crop species. Significantly more quantitative trait loci, genetic maps and markers are available in MapViewer, a new visualization tool that better integrates with other pages in GDR. Pathways can be accessed through the new GDR Cyc Pathways databases, and synteny among the newest genome assemblies from eight species can be viewed through the new synteny browser, SynView. Collated single-nucleotide polymorphism diversity data and phenotypic data from publicly available breeding datasets are integrated with other relevant data. Also, the new Breeding Information Management System allows breeders to upload, manage and analyze their private breeding data within the secure GDR server with an option to release data publicly.

Annual and Perennial Alleyway Cover Crops Vary in Their Effects on Pratylenchus penetrans in Pacific Northwest Red Raspberry (Rubus idaeus).

Cover crops can provide many benefits to agroecosystems, such as lessening soil erosion and increasing water infiltration. However, cover crop use is not common in established red raspberry (Rubus idaeus) fields in the Pacific Northwest. Raspberry growers are concerned about resource competition between the cover crop and raspberry crop, as well as increasing population densities of the plant-parasitic nematode Pratylenchus penetrans, which has a wide host range and has been shown to reduce raspberry plant vigor and yield. A 2-yr study was conducted in an established 'Meeker' raspberry field in northwest Washington to evaluate the effects of nine alleyway cover crops, mowed weed cover, and the industry standard of bare cultivated soil on P. penetrans population dynamics, raspberry yield, and fruit quality. The host status for P. penetrans of cover crops included in the field experiment, as well as Brassica juncea 'Pacific Gold' and Sinapis alba 'Ida Gold', was also evaluated in greenhouse experiments. In the field experiment, P. penetrans population densities did not increase in alleyway cover crop roots over time or in alleyway soil surrounding cover crop roots (means range from 0 to 116 P. penetrans/100 g of soil) compared with the bare cultivated control (means range from 2 to 55 P. penetrans/100 g of soil). Pratylenchus penetrans populations did not increase over time in raspberry grown adjacent to alleyways with cover crops (means range from 1,081 to 6,120 P. penetrans/g of root) compared with those grown adjacent to bare cultivated soil alleyways (means range from 2,391 to 5,536 P. penetrans/g of root). Raspberry grown adjacent to bare cultivated soil did not have significantly higher yield or fruit quality than raspberry grown adjacent to cover crops in either year of the experiment. In the greenhouse assays, 'Norwest 553' wheat and a perennial ryegrass mix were poor hosts for P. penetrans, whereas 'Nora' and 'TAM 606' oat and 'Pacific Gold' and 'Ida Gold' mustard were good hosts. These results support the idea that the potential benefits of alleyway cover crops outweigh the potential risk of increasing P. penetrans population densities and do not compromise raspberry yield or fruit quality.