Tree Fruit Research Laboratory

Soil- and plant-associated environments harbor numerous bacteria that produce antibiotic metabolites with specific or broad-spectrum activities against coexisting microorganisms. The function and ecological importance of antibiotics have long been assumed to yield a survival advantage to the producing bacteria in the highly competitive but resource-limited soil environments through direct suppression. Although specific antibiotics may enhance producer persistence when challenged by competitors or predators in soil habitats, at subinhibitory concentrations antibiotics exhibit a diversity of other roles in the life history of the producing bacteria. Many processes modulated by antibiotics may be inherently critical to the producing bacterium, such as the acquisition of substrates or initiation of developmental changes that will ensure survival under stressful conditions. Antibiotics may also have roles in more complex interactions, including in virulence on host plants or in shaping the outcomes of multitrophic interactions. The innate functions of antibiotics to producing bacteria in their native ecosystem are just beginning to emerge, but current knowledge already reveals a breadth of activities well beyond the historical perspective of antibiotics as weaponry in microbial conflicts.

Soil microbiomes may be harnessed for plant health

Identification of the biological properties contributing to the function of suppressive soils is a necessary first step to the management of such systems for use in the control of soilborne diseases. The development and application of molecular methods for the characterization and monitoring of soil microbial properties will enable a more rapid and detailed assessment of the biological nature of soil suppressiveness. Although suppressive soils have provided a wealth of microbial resources that have subsequently been applied for the biological control of soilborne plant pathogens, the full functional capabilities of the phenomena have not been realized in production agricultural ecosystems. Cultural practices, such as the application of soil amendments, have the capacity to enhance disease suppression, though the biological modes of action may vary from that initially resident to the soil. Plants have a distinct impact on characteristics and activity of resident soil microbial communities, and therefore play an important role in determining the development of the disease-suppressive state. Likewise, plant genotype will modulate these same biological communities, and should be considered when developing strategies to exploit the potential of such a natural disease control system. Implementation of consistently effective practices to manage this resource in an economically and environmentally feasible manner will require more detailed investigation of these biologically complex systems and refinement of currently available methodologies.

Replant disease of apple is common to all major apple growing regions of the world. Difficulties in defining disease etiology, which can be exacerbated by abiotic factors, have limited progress toward developing alternatives to soil fumigation for disease control. However, the preponderance of data derived from studies of orchard soil biology employing multidisciplinary approaches has defined a complex of pathogens/parasites as causal agents of the disease. Approaches to manipulate microbial resources endemic to the orchard soil system have been proposed to induce a state of general soil suppressiveness to replant disease. Such a long-term strategy may benefit the existing orchard through extending the period of economic viability and reduce overall disease pressure to which young trees are exposed during establishment of successive plantings on the site. Alternatively, more near-term methods have been devised to achieve specific quantitative and qualitative changes in soil biology during the period of orchard renovation that may lead to effective disease suppression.

An ethylene action inhibitor, MCP, was applied to preclimacteric and climacteric apple [ Malus sylvestris L. (Mill.) var. domestica Borkh. Mansf.] fruit. Experiments were conducted in North Carolina and Washington State utilizing the following cultivars: Fuji, Gala, Ginger Gold, Jonagold, and Delicious. MCP inhibited loss of fruit firmness and titratable acidity when fruit were held in storage at 0 °C up to 6 months and when fruit were held at 20 to 24 °C for up to 60 days. For all cultivars except `Fuji', differences in firmness between treated and nontreated fruit exceeded 10 N after 6 months storage. These beneficial effects were seen in both preclimacteric and climacteric fruit. Ethylene production and respiration were reduced substantially by MCP treatment. MCP-treated fruit had soluble solids equal to or greater than those in nontreated fruit. Storage and shelf life were extended for all cultivars tested. Chemical name used: 1-methylcyclopropene (MCP).

Historical variability of fire regimes must be understood within the context of climatic and human drivers of disturbance occurring at multiple temporal scales. We describe the relationship between fire occurrence and interannual to decadal climatic variability (Palmer Drought Severity Index [PDSI], El Niño/Southern Oscillation [ENSO], and the Pacific Decadal Oscillation [PDO]) and explain how land use changes in the 20th century affected these relationships. We used 1701 fire‐scarred trees collected in five study sites in central and eastern Washington State (USA) to investigate current year, lagged, and low frequency relationships between composite fire histories and PDSI, PDO, and ENSO (using the Southern Oscillation Index [SOI] as a measure of ENSO variability) using superposed epoch analysis and cross‐spectral analysis. Fires tended to occur during dry summers and during the positive phase of the PDO. Cross‐spectral analysis indicates that percentage of trees scarred by fire and the PDO are spectrally coherent at 47 years, the approximate cycle of the PDO. Similarly, percentage scarred and ENSO are spectrally coherent at six years, the approximate cycle of ENSO. However, other results suggest that ENSO was only a weak driver of fire occurrence in the past three centuries. While drought and fire appear to be tightly linked between 1700 and 1900, the relationship between drought and fire occurrence was disrupted during the 20th century as a result of land use changes. We suggest that long‐term fire planning using the PDO may be possible in the Pacific Northwest, potentially allowing decadal‐scale management of fire regimes, prescribed fire, and vegetation dynamics.

Understanding spatial and temporal patterns present in ectomycorrhizal fungal community structure is critical to understanding both the scale and duration of the potential impact these fungi have on the plant community. While recent studies consider the spatial structure of ectomycorrhizal communities, few studies consider how this changes over time. Ectomycorrhizal root biomass and the similarity of community composition were measured at scales up to 20 cm replicated in nine plots and over 3 yr. Soil cores were additionally stratified into three depths. Annual occurrence of the dominant ectomycorrhizal species was constant at larger spatial scales but varied more across years at a fine spatial scale. Turnover of ectomycorrhizal species between years was observed frequently at scales < 20 cm. The ectomycorrhizal community within a plot was more similar across years than it was to other plots sampled in the same year. Our results demonstrate the dynamic nature of the ectomycorrhizal community even in the absence of large-scale disturbances. The potential role of root turnover and drought stress is discussed.

Forest landscapes across western North America (wNA) have experienced extensive changes over the last two centuries, while climatic warming has become a global reality over the last four decades. Resulting interactions between historical increases in forested area and density and recent rapid warming, increasing insect mortality, and wildfire burned areas, are now leading to substantial abrupt landscape alterations. These outcomes are forcing forest planners and managers to identify strategies that can modify future outcomes that are ecologically and/or socially undesirable. Past forest management, including widespread harvest of fire- and climate-tolerant large old trees and old forests, fire exclusion (both Indigenous and lightning ignitions), and highly effective wildfire suppression have contributed to the current state of wNA forests. These practices were successful at meeting short-term demands, but they match poorly to modern realities. Hagmann et al. review a century of observations and multi-scale, multi-proxy, research evidence that details widespread changes in forested landscapes and wildfire regimes since the influx of European colonists. Over the preceding 10 millennia, large areas of wNA were already settled and proactively managed with intentional burning by Indigenous tribes. Prichard et al. then review the research on management practices historically applied by Indigenous tribes and currently applied by some managers to intentionally manage forests for resilient conditions. They address 10 questions surrounding the application and relevance of these management practices. Here, we highlight the main findings of both papers and offer recommendations for management. We discuss progress paralysis that often occurs with strict adherence to the precautionary principle; offer insights for dealing with the common problem of irreducible uncertainty and suggestions for reframing management and policy direction; and identify key knowledge gaps and research needs.

1-Methylcyclopropene (MCP) was used to evaluate the role of ethylene in development of apple (Malus x domestica Borkh.) physiological disorders during storage. Granny Smith, Red Chief Delicious, and Fuji apple fruit were treated with MCP at a concentration of 1 microL L(-)(1) for 12 h at 20 degrees C. For all varieties stored at 0 degrees C, ethylene production and respiration rates were reduced for several months following MCP treatment, and firmness and titratable acidity of treated fruit were higher compared to controls. Apples treated with MCP did not develop superficial scald or peel greasiness through 6 months storage plus ripening at 20 degrees C for 7 days. Core flush was not observed in MCP-treated fruit until 6 months after treatment when the incidence was still lower compared to control fruit. MCP delayed the rise in production of alpha-farnesene and reduced accumulation of its oxidation products.

Abstract Sunburn is a physiological disorder of apples and other fruit species caused by excess solar radiation. Damage occurs in practically all growing regions of the world, causing severe crop loss every year. Direct factors required for induction of the three currently-known types of sunburn (i.e., sunburn necrosis, sunburn browning, and photooxidative sunburn) include excess radiant heating and/or exposure to excess sunlight. Several other factors (e.g., relative humidity, wind velocity, acclimation of fruit, and cultural management practices), which alone cannot induce sunburn damage, indirectly influence the induction of sunburn by interacting with the direct factors to influence the appearance and severity of the symptoms. Sunburn affects apple fruit at many levels; it causes structural and morphological changes, alters pigment composition, influences adaptive mechanisms, impairs photosynthesis, and consequently decreases fruit quality. Fruits employ multiple physiological and biochemical mechanisms as complex defense systems to minimize damage. Photoprotective pigments, antioxidant enzymes and metabolites, heat-shock proteins, and the xanthophyll cycle help mitigate damage, but are often inadequate under field conditions to fully protect from sunburn. Quality loss significantly affects postharvest behavior, marketing and consumer acceptance of fruit. Internal fruit quality (e.g., firmness, soluble solids concentration, and titratable acidity) is affected by sunburn, and changes in these traits continue during cold storage. Sunburn-related disorders (e.g., sunburn scald in ‘Granny Smith’ and ‘Fuji’ stain) can appear in cold storage. There are several methods with various modes of action (e.g., climate ameliorating techniques, and sunburn suppressants) available to growers to decrease sunburn under field conditions. At the end of this review, the potential impact of a changing climate on sunburn incidence is considered, as both UV-B radiation and temperature are projected to change. Finally, several topics that need further research are discussed. Keywords: Malus × domestica Borkh.solar radiationheat stressUV-B radiationclimate changefruit qualitysunscald ACKNOWLEDGMENT Authors thank Dr. Donald C. Elfving (Washington State University) for critical reading of the manuscript and valuable advice for improvements. Salaries and research support were provided in part by State and Federal Funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. Journal Manuscript Number HCS 12-07.

Abstract Our review gives a comprehensive overview of the chemical restriction of plant growth. The first portion of the article gives a brief history of plant growth retardants followed by an update on current usage. Following this, the biochemical and physiological aspects of plant growth restriction are covered. The remaining portion of the review deals with current and potential uses of plant growth retardants on amenity plants, fruit trees, cereals and grains, and vegetables. The concluding section emphasizes future directions for growth retardant research. Key words: gibberellin biosynthesis inhibitorsgrowth retardantsplant growth regulatorsshoot growth inhibitors Notes Contribution No. 26096 from the Texas Agricultural Experiment Station. Mention of a proprietary product or vendor does not constitute an endorsement. Mention of a compound for a specific agricultural application does not imply that the product is necessarily registered for such use.

Methyl bromide is a widely used fumigant for both pre-plant and post-harvest pest and pathogen control. The Montreal Protocol and the US Clean Air Act mandate a phase-out of the import and manufacture of methyl bromide, beginning in 2001 and culminating with a complete ban, except for quarantine and certain pre-shipment uses and exempted critical uses, in January 2005. In 1995, ARS built on its existing programs in soil-borne plant pathology and post-harvest entomology and plant pathology to initiate a national research program to develop alternatives to methyl bromide. The focus has been on strawberry, pepper, tomato, perennial and nursery cropping systems for pre-plant methyl bromide use and fresh and durable commodities for post-harvest use. Recently the program has been expanded to include research on alternatives for the ornamental and cut flower cropping systems. An overview of the national research program is presented. Results from four specific research trials are presented, ranging from organic to conventional systems. Good progress on short-term alternatives is being made. These will be used as the foundation of integrated management systems which begin with pre-plant management decisions and continue through post-harvest processing.

Brassicaceae seed meal (SM) formulations were compared with preplant 1,3-dichloropropene/chloropicrin (Telone-C17) soil fumigation for the ability to control apple replant disease and to suppress pathogen or parasite reinfestation of organic orchard soils at two sites in Washington State. Preplant soil fumigation and an SM formulation consisting of either Brassica juncea-Sinapis alba or B. juncea-B. napus each provided similar levels of disease control during the initial growing season. Although tree growth was similar in fumigated and SM-amended soil during the initial growing season, tree performance in terms of growth and yield was commonly superior in B. juncea-S. alba SM-amended soil relative to that in fumigated soil at the end of four growing seasons. SM-amended soils were resistant to reinfestation by Pratylenchus penetrans and Pythium spp. relative to fumigated soils and corresponded with enhanced tree performance. Phytotoxic symptoms were observed in response to SM amendment at one of two orchard sites, were dependent upon season of application, and occurred in an SM formulation-specific manner. After 2 years, the rhizosphere microbiome in fumigated soils had reverted to one that was indistinguishable from the no-treatment control. In contrast, rhizosphere soils from the SM treatment possessed unique bacterial and fungal profiles, including specific microbial elements previously associated with suppression of plant-pathogenic fungi, oomycetes, and nematodes. Overall diversity of the microbiome was reduced in the SM treatment rhizosphere, suggesting that enhanced "biodiversity" was not instrumental in achieving system resistance or pathogen suppression.

Particle film technology is a developing pest control system for tree fruit production systems. Trials were performed in Santiago, Chile, and York Springs, Pa., Wenatchee and Yakima, Wash., and Kearneysville, W. Va., to evaluate the effect of particle treatments on apple [ Malus sylvestris (L.) Mill. var. domestica (Borkh) Manst.] leaf physiology, fruit yield, and fruit quality. Leaf carbon assimilation was increased and canopy temperatures were reduced by particle treatments in seven of the eight trials. Yield and/or fruit weight was increased by the particle treatments in seven of the eight trials. In Santiago and Kearneysville, a * values of the fruit surface were more positive in all trials although a * values were not increased in Wenatchee and Yakima. Results indicate that particle film technology is an effective tool in reducing heat stress in apple trees that may result in increased yield potential and quality.

The greenhouse gas (GHG) impact of composting a range of potential feedstocks was evaluated through a review of the existing literature with a focus on methane (CH(4)) avoidance by composting and GHG emissions during composting. The primary carbon credits associated with composting are through CH(4) avoidance when feedstocks are composted instead of landfilled (municipal solid waste and biosolids) or lagooned (animal manures). Methane generation potential is given based on total volatile solids, expected volatile solids destruction, and CH(4) generation from lab and field incubations. For example, a facility that composts an equal mixture of manure, newsprint, and food waste could conserve the equivalent of 3.1 Mg CO(2) per 1 dry Mg of feedstocks composted if feedstocks were diverted from anaerobic storage lagoons and landfills with no gas collection mechanisms. The composting process is a source of GHG emissions from the use of electricity and fossil fuels and through GHG emissions during composting. Greenhouse gas emissions during composting are highest for high-nitrogen materials with high moisture contents. These debits are minimal in comparison to avoidance credits and can be further minimized through the use of higher carbon:nitrogen feedstock mixtures and lower-moisture-content mixtures. Compost end use has the potential to generate carbon credits through avoidance and sequestration of carbon; however, these are highly project specific and need to be quantified on an individual project basis.

d'Anjou cv. pear fruit (Pyrus communis L.) exposed at harvest to 0, 0.42, 4.2, or 42 micromol m(-)(3) 1-methylcyclopropene (1-MCP) for 12 h at 20 degrees C were stored at 1 degrees C for up to 8 months. After storage, half of the fruit was continuously exposed to ethylene (0.45 or 4-18 mmol m(-)(3)) for 7 days at 20 degrees C. All fruit treated with 1-MCP had lower respiration and ethylene production compared to untreated controls. Fruit quality changes were delayed following 1-MCP treatment, as was development of superficial scald and peel yellowing. The duration of 1-MCP-induced responses was dependent on 1-MCP treatment concentration. When 1-MCP-treated fruit began to ripen, softening and production of volatile compounds proceeded similar to that of untreated fruit. Post-storage ethylene exposure did not consistently stimulate ripening of fruit previously treated with 1-MCP. Efficacy of ethylene treatment depended on 1-MCP concentration and storage duration.

Climacteric Fuji apples were treated with 10 microL x L(-1) MCP (1-methylcyclopropene), 2 mmol x L(-1) MJ (methyl jasmonate), or a combination of 10 microL x L(-1) MCP and 2 mmol x L(-1) MJ. Fruit were kept at 20 degrees C for 15 days after treatment. Production of ethylene and other volatile compounds was measured prior to and 3, 7, 11, and 15 days after treatment. Ethylene production decreased 3 days following MJ treatment and then increased. MCP treatment alone or in combination with MJ inhibited ethylene production. MJ and MCP inhibited production of many volatile alcohols and esters. The production of individual alcohols and esters appears to be differentially inhibited by MJ or MCP. MJ and MCP inhibited not only production of alcohols but also formation of esters from alcohols.

BACKGROUND: The amount and structure of genetic diversity in dessert apple germplasm conserved at a European level is mostly unknown, since all diversity studies conducted in Europe until now have been performed on regional or national collections. Here, we applied a common set of 16 SSR markers to genotype more than 2,400 accessions across 14 collections representing three broad European geographic regions (North + East, West and South) with the aim to analyze the extent, distribution and structure of variation in the apple genetic resources in Europe. RESULTS: A Bayesian model-based clustering approach showed that diversity was organized in three groups, although these were only moderately differentiated (FST = 0.031). A nested Bayesian clustering approach allowed identification of subgroups which revealed internal patterns of substructure within the groups, allowing a finer delineation of the variation into eight subgroups (FST = 0.044). The first level of stratification revealed an asymmetric division of the germplasm among the three groups, and a clear association was found with the geographical regions of origin of the cultivars. The substructure revealed clear partitioning of genetic groups among countries, but also interesting associations between subgroups and breeding purposes of recent cultivars or particular usage such as cider production. Additional parentage analyses allowed us to identify both putative parents of more than 40 old and/or local cultivars giving interesting insights in the pedigree of some emblematic cultivars. CONCLUSIONS: The variation found at group and subgroup levels may reflect a combination of historical processes of migration/selection and adaptive factors to diverse agricultural environments that, together with genetic drift, have resulted in extensive genetic variation but limited population structure. The European dessert apple germplasm represents an important source of genetic diversity with a strong historical and patrimonial value. The present work thus constitutes a decisive step in the field of conservation genetics. Moreover, the obtained data can be used for defining a European apple core collection useful for further identification of genomic regions associated with commercially important horticultural traits in apple through genome-wide association studies.

The recent introduction of Drosophila suzukii (Matsumura) into regions of the western United States that produce cherries, Prunus avium (L.), has resulted in the need for insecticide-based management programs close to harvest. These treatments have become problematic because of inconsistencies among export markets regarding maximum residue limits (MRLs) that are allowed for different insecticides on imported fruit. As a result, fruit that was treated and harvested in a safe manner according to the U.S. label issued by the Environmental Protection Agency may or may not qualify for export to countries that have MRLs that are lower than those of the United States, or where MRLs have not yet been established. This project addresses this issue by measuring the degradation curves of six insecticides when applied at 7 or 21 d before the initiation of harvest. Based on the results of these tests, we propose a selection of insecticides that can be used for spotted wing drosophila control, with the number of applications and sequence of insecticides used dependent on pest pressure and the number of days required between application and harvest. Three insecticides with favorable characteristics include lambda-cyhalothrin, spinosad and malathion, which allow producers to incorporate the principles of efficacy, fruit susceptibility, and resistance management and still allows for the export of fruit to all major export markets.

Apples [ Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf. (`Gala', `Delicious', `Granny Smith' and `Fuji')], pretreated or nontreated with 1-methylcyclopropene (1-MCP, 0.6 to 1.0 μL·L –1 for 18 hours at 20 °C), were stored in controlled atmosphere (CA, 1 to 1.5 kPa O 2 ; 1 to 2 kPa CO 2 ) or in regular atmosphere (RA) for up to 8 months at 1 °C. Firmness, titratable acidity (TA), soluble solids content (SSC), and volatile abundance were analyzed every month directly or after transfer to air at 20 °C for 1 week to determine effect of 1-MCP, storage atmosphere and storage time on apple quality immediately after cold storage and after simulated marketing conditions at 20 °C. The 1-MCP ± CA treatments delayed ripening and prolonged storage life as indicated by delayed loss of firmness and TA in all four cultivars during storage. The 1-MCP ± CA also slightly delayed loss of SSC for `Gala' but had no effect on SSC levels for the other cultivars. There were differences among treatments for firmness and TA content [(1-MCP + RA) &gt; CA] for `Gala', `Delicious', and `Granny Smith' apples, but not for `Fuji'. These differences were generally exacerbated after transfer of fruit to 20 °C for 1 week. A combination of 1-MCP + CA was generally best [(1-MCP + CA) &gt; (1-MCP + RA) or CA] for maintaining `Delicious' firmness and TA. However, the treatments that were most effective at retaining TA and firmness also retained the least volatiles. The results indicate that the efficacy of 1-MCP and CA in maintaining apple quality factors is cultivar dependent and that 1-MCP + RA may be a viable alternative to CA for optimal eating quality for some cultivars.