About

Gregory Michael Peck is an Associate Professor and Director of Undergraduate Studies in the Plant Sciences Major within the School of Integrative Plant Science at CALS. His research addresses the challenges of sustainably and profitably producing tree fruits, with extensive experience in fruit-crop production systems across California, Washington, New York, and Virginia. His academic training spans horticulture, plant physiology, soil science, entomology, food science, plant pathology, ecology, agricultural economics, and education. His research focuses on various aspects of tree-fruit production, including identifying, phenotyping, and genotyping cider apple germplasm; developing horticultural practices to improve hard cider quality; sustainable soil and nutrient management; increasing the efficiency of organic apple orchard systems; and crop-load management in apple trees through pollen tube growth modeling. His work aims to develop fruit production systems that support the long-term economic and environmental viability of commercial tree-fruit growers. Peck actively engages with the industry through outreach activities such as meetings, field days, publications, websites, blogs, and social media, providing resources and guidance on organic apple production and hard cider.

Research topics

• Biology
• Horticulture
• Chemistry
• Agronomy
• Food science
• Marketing
• Geography
• Biochemistry
• Business
• Economics

Selected publications

• Root-Zone Microbiome Responds to Organic Mulch Cover by Reducing Fungal Pathogen Load and Boosting Tree Establishment in High-Density Apple Orchards

  Agronomy · 2026-04-05

  articleOpen accessSenior author

  High-density apple (Malus domestica Borkh.) orchards yield fruits as early as three years after planting but nutrient inputs and availability are paramount to a successful orchard; sustainable practices that balance tree growth and production with environmental concerns are not widely available. In this three-year study, we implemented a split-plot design in three orchards across the Mid-Atlantic region of the USA to evaluate integrated soil management approaches that combine locally sourced carbon-based organic mulch with fertilizers on rhizosphere microbes and tree growth. Bacterial and fungal communities were sampled at the end of the first and third growing seasons in addition to soil and tree-related physicochemical properties. Mulch treatment showed the most significant effect on both the bacterial and fungal groups. Most of these changes reflect the increase in soil organic matter and the increase in carbon cycling. Sequence variants belonging to Flavobacteria and Cytophaga were enriched by the mulch application. A key result from this project is the suppression of the relative abundance of potential soil-borne plant fungal pathogens in all orchards in all years. Additionally, arbuscular mycorrhizal fungi were enriched under the mulch treatment. Microbial shifts accompanying the mulch treatments supported higher trunk cross-sectional areas by the third sampling year that increased by 33.5%. Fertilizer treatments had less pronounced effects on microbial communities. These results highlight the potential for using sustainable, integrated nutrient management strategies to promote healthy orchard soils and support vigorous tree growth while reducing fungal pathogens. Our work will contribute to regional and location-specific fertilizer recommendations for apple producers.

  PublisherDOI

• Integrated Approaches Are Needed To Manage Weeds in Organic Apple Orchards

  HortScience · 2025-03-14 · 1 citations

  articleOpen accessSenior author

  Prolific weed growth during rainy, humid summers coupled with poor efficacy of available weed management strategies remains a major barrier to adoption of organic apple production in New York. The effects of multiple, in-row weed management strategies on weed cover and biomass, soil health, and tree growth and productivity were assessed via a split-plot experiment implemented in 2016 in a certified organic apple orchard in Ithaca, NY, USA. Main treatments included cultivation with a Wonder Weeder (cultivation), surface-applied wood chip mulch (mulch), and an untreated control (main). Split treatments included ammoniated soap of fatty acids (ammoniated soap), capric/caprylic acid (capric acid), mowing with a string trimmer (mowing), and an untreated control (split). The mulch was applied once, in Spring 2016; all other treatment combinations occurred four times per season, about monthly from May to August. Between 2017 and 2019, nearly all measured soil health parameters increased under the mulch treatment relative to the control (main) treatment. Notably, soil organic matter in the mulch treatment increased from 4.8% in 2016 to 5.2% in 2019 but declined in the cultivation treatment from 4.5% to 4.1% during those years. Regardless of the split treatment, the mulch treatment maintained 16% to 45% less weed biomass than the other main treatments throughout the study. The split treatments became a more significant factor in the latter years. Regardless of the main treatment, the split treatments of ammoniated soap, capric acid, and mowing all maintained less than 200 g·m −2 of weed biomass per sampling period, which was significantly less than the control (split) at sample dates 3 and 4 in 2017 and sample dates 2 to 4 in 2018 and 2019. This was mainly due to an abundance of Symphytotrichum lanceolatum and Solidago spp. in main treatment combinations with the control (split) treatment. Tree growth was greatest in the cultivation treatment, in which trunk cross-sectional area quadrupled between Spring 2016 and Fall 2019. These findings demonstrate that multiple approaches are needed to obtain adequate weed control and balance orchard productivity and soil health during the establishment period of an organic apple orchard in New York.

  PublisherDOI

• Reduced apple crop density enhances total polyphenol accumulation via upregulation of anthocyanidin reductase and other phenylpropanoid pathway genes

  Frontiers in Plant Science · 2025-06-09 · 4 citations

  articleOpen accessSenior authorCorresponding

  ) juice by providing flavor, aroma, color, and microbial stability. However, polyphenol concentration in apple fruit can fluctuate by 50% or more from tree-to-tree within an orchard of the same scion and rootstock resulting in significant year-to-year product variability. In order to better understand polyphenol biosynthesis in cider apples, four-year-old 'Porter's Perfection' and 'Binet Rouge' trees were left unthinned (control), or had fruitlets adjusted to low, medium, or high crop density. Fruit peel and flesh tissue were sampled at 27, 81, and 160 (harvest) days after full bloom (DAFB) and analyzed for polyphenol concentration and composition, as well as gene expression. At 160 DAFB, there was a 39% increase in monomeric and oligomeric polyphenol concentrations in the 'Porter's Perfection' flesh tissue of the reduced crop density treatments as compared to the unthinned control. The transcriptome profile of the low crop density 'Porter's Perfection' treatment indicated that genes encoding enzymes that catalyze critical functions in the phenylpropanoid pathway such as hydroxylation, methylation, and glycosylation were upregulated compared to the control at 27 DAFB and 81 DAFB. The period of upregulated gene expression corresponded with increased concentration of polyphenols, particularly proanthocyanidin monomers and oligomers. Specifically, there was a significant increase in anthocyanidin reductase (an enzyme involved in epicatechin catalysis) expression in the low crop density treatment relative to the unthinned control at 27 and 81 DAFB in both the peel and flesh. Reduced crop densities enhanced the expression of genes involved in the phenylpropanoid pathway in apples, which likely increased fruit polyphenols. Furthermore, we identified eight and three novel ethylene response factor genes, 26 and 14 MYB-bHLH genes in the flesh and peel, respectively, that are potentially involved in regulating proanthocyanidin biosynthesis. These data suggest that reduced crop load densities lead to enhanced polyphenol synthesis and accumulation in 'Porter's Perfection' apples via transcriptional regulation of anthocyanidin reductase and other genes in the phenylpropanoid pathway.

  PublisherOA PDFDOI

• 'Honeycrisp': the challenge of the apple crisp revolution

  Fruit Research · 2025-01-01 · 1 citations

  articleOpen accessSenior author

  'Honeycrisp' apples are a crisp cultivar known for their unique texture and flavor. This cultivar is considered revolutionary in the world of crispy apples due to its high value and strong consumer preference. Many new cultivars have recently been developed using 'Honeycrisp' as a parent. However, growing, producing, storing, and marketing 'Honeycrisp' apples present significant challenges. A holistic approach to 'Honeycrisp' production will be discussed, covering aspects such as soil health, rootstocks, orchard management, environmental factors, physiological disorder development, storage protocols, and marketing strategies for sustainable production.

  PublisherOA PDFDOI

• Early Season Tree Shading Decreases Phenolic Acids and Quercetin Glycosides, But Not Proanthocyanidin Monomer and Oligomer Concentrations in Cider Apples at Harvest

  SSRN Electronic Journal · 2025-01-01

  preprintOpen accessSenior author
  PublisherDOI

• Apple rootstocks affect mineral nutrient uptake in organic orchards

  Acta Horticulturae · 2025-06-01

  article
  PublisherDOI

• Reduced Sorbitol Genotype Alters Postharvest Microbiomes of ‘Greensleeves’ Apples

  Journal of the American Society for Horticultural Science · 2025-09-01 · 2 citations

  articleOpen access

  Fruit microbiomes are capable of protecting their hosts from harmful pathogens and aiding in biocontrol; therefore, it is important to understand how differences in host genotype shape fruit microbial communities. The fruit species and even cultivars within a species can harbor different fruit microbiomes, but it has been difficult to establish how a single host gene can shape the microbiome structure. We investigated two genotypes of ‘Greensleeves’ apples with reduced sorbitol biosynthesis through antisense suppression of aldose 6-phosphate reductase with the wild type (WT) to assess how sugar composition of the fruit surface impacts microbial communities. We hypothesized that reduced sorbitol genotypes A4 and A10 would show an epiphytic microbiome different from that of the WT that corresponds to a difference in sugar composition on the fruit surface at harvest and during storage with and without postharvest treatment of fruit with 1-methycyclopropene (1-MCP), which is an inhibitor of ethylene perception. Throughout the sampling window (at harvest, 7 weeks storage, 13 weeks storage) across the 2 years of the study, the genotype, but not 1-MCP, was a significant predictor of microbiome composition. The A10 and A4 lines had an increased abundance of the pathogenic fungal genus Acremonium compared with that of the WT in one year. However, while A4 and A10 had different sugar compositions than that of WT in fruit flesh, no differences on the fruit surface were found. In addition, A4 and A10 showed microbiomes that were different from each other as well as different from that of the WT despite having the same reduced sorbitol phenotype, thus making it difficult to link microbiome differences to a specific physiological mechanism. This work represents an important step in showing the first example, to our knowledge, of how the cascading effects resulting from silencing a single gene can impact the assembly of postharvest fruit microbiomes.

  PublisherDOI

• A bittersweet symphony: genetic insights into cider apple fruit quality

  G3 Genes Genomes Genetics · 2025-10-19

  articleOpen accessSenior author

  Many traditional cider apples (Malus domestica) have unique chemotypic traits that impact the sensory profile and fermentation characteristics of the final product. In particular, cider apples may have greater polyphenol, organic acid, and sugar concentration than fresh-market apples. Despite historic importance and a growing market in many parts of the world, the genetic basis underlying cider apple fruit quality remains poorly understood. Therefore, few functional genetic markers have been successfully adapted for cider apple breeding. Using a genome-wide association study on 253 cider apple accessions from the USDA Malus collection, we identified 19 significant marker-trait associations for fruit quality traits. Notably, we identified a distinct marker on chromosome 15 that was strongly associated with total polyphenols, a key determinant of bitterness and astringency. A major association on chromosome 16, near the Ma1 locus, explained a substantial proportion of the phenotypic variance for titratable acidity and pH, confirming the importance of this region. Using these 2 loci, we were able to distinguish between cider apple groups, especially for bittersweet apples. A major locus on chromosome 1 was linked to the ratio of glucose and sucrose. This locus could be targeted to select genotypes with increased glucose content, which could improve fermentation kinetics. Overall, these results provide a robust genetic analysis focusing on quality traits in a cider-specific germplasm, laying the foundation for identifying apple cultivars with desirable attributes for cider production from germplasm collections and for making marker-assisted selections within breeding programs.

  PublisherOA PDFDOI

• Cider Apple Harvest Maturity and Preharvest Drop Can Be Effectively Managed with Aminoethoxyvinylglycine, 1-Naphthaleneacetic Acid, and Ethephon

  HortTechnology · 2025-06-30

  articleOpen access1st authorCorresponding

  Certain European high-tannin cider apple ( Malus × domestica Borkh.) cultivars used for commercial production of craft hard cider (fermented apple juice) are known to have severe preharvest fruit drop, as well as asynchronous ripening. A 2-year (2018 and 2019) study at two commercial orchards in Wayne County, NY, USA, examined the effects on drop and ripeness of applying three plant growth regulators—aminoethoxyvinylglycine (AVG), ethephon (ETH), and 1-naphthaleneacetic acid (NAA)—on eight different cider apple cultivars. The treatments included i) untreated control, ii) ETH applied 1 week before harvest (WBH), iii) NAA applied 4 and 2 WBH, iv) NAA at 4 and 2 WBH plus ETH at 1 WBH, v) AVG at 4 and 2 WBH, and vi) AVG at 4 and 2 WBH plus ETH applied 1 WBH. Treatments had significant effects on fruit drop: AVG and NAA treatments significantly reduced drop, while NAA+ETH promoted drop, relative to the control. AVG delayed ripening, while NAA+ETH accelerated ripening. Cultivars that tended to have greater natural preharvest fruit drop had a greater reduction in fruit drop when treated with NAA or AVG. Our research can lead to more precise management of cider apple harvest. For example, NAA alone encouraged ripening while reducing drop, which would be advantageous for over-row machine harvest followed soon thereafter by fruit processing. NAA combined with ETH resulted in advanced ripening, reduced fruit detachment force, and fruit drop largely being condensed into the week leading up to harvest, which may be advantageous for shake-and-sweep mechanical harvest followed by short-term storage. AVG alone delayed ripeness and reduced fruit drop, while increasing flesh firmness and fruit detachment force, making this plant growth regulator (PGR) more suitable for hand harvest and long-term storage before processing.

  PublisherDOI

• Mistaken Identity: Correcting the Conflation of Malus ‘Virginia Crab’ (Foster) with Malus ‘Hughes Virginia Crab’

  Journal of American Pomological Society · 2025-11-22

  articleOpen accessSenior author

  Genetic analysis of Malus ‘Virginia Crab’ (PI 589324) has revealed this widely plantedcrabapple to be a triploid hybrid of Malus ‘Manchurian’ (PI 588989) and an unknown second parent. The ‘Virginia’ crabapple (PI 589324) has widely been assumed to be synonymous with ‘Hughes’ or ‘Hewes’ crabapple of Virginian origin, historically revered for cidermaking in America since the early eighteenth century. The authors present phenotypic, genetic, and historical evidence that ‘Virginia Crab’ and ‘Hughes Virginia Crab’ represent two distinct genotypes. We propose renaming PI 589324 ‘Foster’s Virginia Crab’ to avoid future conflation. It is unclear at this time if the true-to-type ‘Hughes Virginia Crab’ is still extant, and if so, where it is held.

  PublisherOA PDFDOI

Frequent coauthors

• Amanda C. Stewart

  Virginia Tech

  31 shared

• Sihui Ma

  University of Illinois Urbana-Champaign

  22 shared

• Andrew P. Neilson

  North Carolina State University

  21 shared

• Brianna L. Ewing

  Black & Veatch (United Kingdom)

  16 shared

• L.D. Combs

  Virginia Cooperative Extension

  11 shared

• Keith S. Yoder

  Virginia Tech

  11 shared

• Candace N. DeLong

  10 shared

• Ian A. Merwin

  Cornell University

  8 shared

Labs

• Gregory Michael PeckPI

Education

• Ph.D., Horticulture

  Cornell University

  2009

• MS, Horticulture

  Washington State University

  2004

• BA, Comparative Religion

  University of Vermont

  1994

Awards & honors

• Pi Alpha Xi, The National Honor Society for Horticulture. Ho…
• Cornell Graduate & Professional Student Assembly. Teaching,…
• American Cider Association. Grower Advocate of the Year (201…
• State Horticultural Association of Pennsylvania. George A. G…
• American Society for Horticultural Science. Outstanding Exte…