Location: Fruit and Tree Nut Research
2020 Annual Report
Objectives
1. Improve pecan nut productivity by analyzing key horticultural issues that disrupt annual consistency, yield, and quality, and developing new or improved mitigation strategies. 1.A. Determine if canopy exposure to nano-particles, in particular zinc and nickel nano-particles can improve health and longevity of pecan tree canopies. 1.B. Characterize horticultural traits of native pecan germplasm and identify genes of interest as a resource for development of new and improved cultivars. 1.C. Characterization of improved pecan rootstocks for uniformity of yield and enhanced productivity. 2. Reduce impacts of the most important pecan diseases on production, quality and uniformity of nutmeats. 2.A. Characterize and identify novel ways to improve management of pecan scab in tree canopies based on inoculum sources, fungicide spray coverage, disease distribution and methods for disease management. 2.B. Determine dynamics of population genetic diversity of Venturia effusa in pecan orchards.
Approach
This research aims to provide pecan farmers with improved, sustainable tree and disease management practices that stabilize yield in pecan (Carya illinoinensis) orchards. The management tools and strategies will enable farmers to mitigate alternate bearing (AB) and further loss in yield caused by disease. AB is considered the most important biological problem facing pecan production: it is economically harmful, resulting in excessive year-to-year fluctuation in nut yield and kernel quality. Many biotic and abiotic factors can induce or increase the amplitude of AB. How factors associated with canopy health, particularly nutrition, rootstock, and disease affect AB represent some of the knowledge gaps that limit development of suitable tools for stabilizing nut production and reducing yield losses. The research targets 1. Whether use of nano-fertilizers can provide a basis for more efficient nutrient management, stable and greater production of pecan, while ensuring better environmental security. 2. Characterizing phenotypic traits of native pecan germplasm in conjunction with genome wide analyses to identify traits to incorporate into improved cultivars. 3. Characterization of the role rootstocks in tree growth and productivity, to provide a basis for more uniform, consistent and thus sustainable production of pecan nutmeats. 4. Determining how inoculum sources of pecan scab (caused by Venturia effusa) contribute to the epidemic, and using this information to develop new disease management tools, thereby reducing the impact of scab in susceptible pecan cultivars, and 5. Understanding the population genetics of the scab pathogen to underpin deployment of more durable host resistance in the future. A series of field and laboratory studies over the next five years will address these key areas where knowledge is lacking; the resulting information will provide the basis for novel management products that improve horticultural and disease management and favor canopy health in pecan.
Progress Report
ARS researchers at Byron, Georgia, initiated a greenhouse study to determine the effect of canopy exposure to nano-particles, in particular essential micronutrients zinc and nickel. The experiment was carried out on two cultivars ‘Byrd’ and ‘Zinner’. The effects of foliar application of zinc and nickel nano-particles is being compared to conventional micronutrient applications on pecan seedlings as a means to improve health and longevity of pecan trees, while reducing wastage and cost of application. The use of nano-fertilizers will allow more economic, sustainable and precise fertilization for pecan production.
ARS researchers at Byron, Georgia, initiated data collection of agronomically and horticulturally valuable traits in a provenance collection of pecan. Characterization of bud break and flowering time has been completed in the provenance collection housed at ARS, Byron, Georgia. Additional tree canopy data based on remote sensing technology is being analyzed. Nut traits, including fatty acid profiles of trees resistant to scab are being assessed. These traits are important for future breeding programs and will contribute to more improved, more sustainable production and will benefit the health value of the pecan nut.
ARS researchers at Byron, Georgia, conducted research to evaluate dwarfing hickory rootstocks on tree productivity, and graft compatibility and assess tree yield. The effect of hickory species as rootstocks can provide useful information on their value for tree dwarfing and other traits, including drought tolerance, while maintaining tree productivity and overall tree health. The trees have been characterized using remote sensing and mapping technology to compare various horticultural parameters. The information will contribute to future, more efficient, improved pecan production systems.
Pecan root-knot nematode (Meloidogyne partityla) is a constraint to pecan cultivation. Nematode parasitism was previously reported to be associated with zinc and nickel deficiency and mouse ear disorder. The evaluation of three different rootstock susceptibilities to pecan root-knot nematode was carried out in a greenhouse at University of Georgia in Athens, Georgia. The susceptibility of pecan rootstocks to pathogenic nematodes will allow for a better understanding of mouse ear severity related to nickel and other cation deficiencies and selection of appropriate rootstocks to enhance orchard productivity where nematode parasitism is an issue.
An experiment was established by ARS researchers at Byron, Georgia, to better understand pecan scab disease epidemic development in pecan trees. Trees were hedge pruned or not, and will either be sprayed with fungicide or not, and scab disease incidence and severity assessed on foliage, fruit and shoots. Results will be analyzed and will be used to ascertain how early season shoot infections vary in the differently managed trees, and how this impacts scab disease development on foliage and fruit early in the season. The information will aid fungicide applications timing to better manage shoot lesions in hedge-pruned and non-hedged pecan trees.
Field experiments were established by ARS researchers at Byron, Georgia, to monitor the activity of pecan scab disease lesions throughout the year on three cultivars of pecan. The numbers of spores produced on lesions on shoot samples will be monitored to determine periods of lesion activity. This will help identify the critical period of conidial production from shoot lesions, particularly that early in the season which is considered the primary source of infection for the epidemic, which will pave the way for more appropriately targeted fungicide applications.
A long-term study was continued by ARS researchers at Byron, Georgia, to explore the effect of prolonged cycles of mechanical hedge-pruning on pecan scab and tree health compared to non-hedge-pruned trees. Results confirm that hedging benefits scab management by allowing a greater proportion of the fruit to be effectively protected by efficacious fungicide coverage. This has ramifications for management of scab susceptible cultivars in the southeastern United States. But long-term effects of hedge pruning on pecan disease development are not known. Results are being analyzed. Mechanical hedge-pruning is beneficial to maximizing canopy coverage with fungicide to reduce scab severity of the nut crop.
Samples of scab-diseased overwintering shoot, leaf and shuck material were collected and examined by ARS researchers at Byron, Georgia, for evidence of structures that could be the sexual stage of the scab pathogen (Venturia effusa). A spore sampler was operated in the field by ARS researchers at Byron, Georgia, to collect samples of air-borne spores to determine whether any could be identified as the sexually produced ascospore of the pecan scab pathogen. Identification of the sexual stage in the field will have major ramifications for our understanding of the epidemiology of the disease, and may provide useful new points for control.
An experiment was continued by ARS researchers at Byron, Georgia, to determine characteristics of populations of the pecan scab pathogen collected from different cultivars. No studies have been done to establish whether populations from cultivars grown alongside each other are freely recombining and conceivably have the potential to develop “super race” of scab able to infect multiple cultivars. Results will provide valuable insights into populations genetic dynamics of scab pathogen populations to help guide resistance breeding efforts.
Research was initiated by ARS researchers at Byron, Georgia, to develop improved approaches to analyzing data from ordinal scales used for the assessment of pecan scab and other plant diseases. The ramifications of rating methods and analysis, particularly when using disease ordinal scales, can be problematic. The work aims to ensure accurate and reliable estimation and analysis of pecan scab and other diseases.
Accomplishments
