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United States Department of Agriculture

Agricultural Research Service

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Location: Fruit and Nut Research

2011 Annual Report

1a.Objectives (from AD-416)
1. Provide improved horticultural tools for stabilizing pecan nut yields in alternate bearing pecan trees and orchards.

2. Develop an improved approach for orchard management of fungal diseases attacking developing fruit, based on enhancement of the tree's natural disease resistance mechanisms.

1b.Approach (from AD-416)
Objectives are achieved via research and development efforts to introduce to commercial pecan producers new horticultural tools to improve production efficiency of commercial enterprises. The approach focuses on alternate bearing and pecan scab disease via introduction of the following tools: a chemical-based thinning strategy for regulation of crop-load; regulation of flowering and alternate bearing via plant growth regulators; an improved “conceptual tool” for managing alternate bearing; reduction of chemical stresses by improved nutrient element management with emphasis on zinc; and induction of greater natural tree resistance to fungal disease pests (such as pecan scab) via improved tree nutrition and systemic acquired resistance inducers. The approach includes numerous lab, greenhouse, and field based studies, but with a great deal of emphasis on field evaluation of treatments in real-world commercial orchard situations. Extension specialists are included in the research efforts to facilitate transfer of knowledge, strategies, and technologies to farmers. The approach largely relies on adaptation of existing technologies to pecan horticulture, but with new technology potentially being introduced for transition and inner-transition metals, and registration of existing commercial products for usage on pecan. There will be dozens of research studies conducted, with experimental designs structured to test hypotheses associated with objective-linked postulates. Results will be disseminated to scientific, extension, and commercial individuals and groups via appropriate publications/articles, talks, and field-days.

3.Progress Report
Chemical thinning: Excessive inconsistence in calcium hydroxide sprays to fruit-thin pecan trees means that an alternative approach merits pursuit. Additionally, it was determined that direct chemical thinning of fruit is unlikely to be efficacious for pecan due to the small number of fruit per fruiting cluster. The approach subsequent progressed to using gibberellic acid in “on” phase cropping years to reduce return bloom in the subsequent year—i.e., indirect thinning. Retention of fruit in the “off” phase year appeared feasible via timely usage of ReTain (an ethylene inhibitor) to prevent fruit abortion in June.

Alternate bearing: Research validates that flowering and alternate bearing is regulated initially via balances involving plant growth regulators and then subsequently via carbohydrate reserves during vernalization; thus, leading to new approach using timely treatments with certain plant hormones to regulate subsequent year flowering.

Zinc stress: Field studies in Georgia, Oklahoma, and New Mexico indicate that usage of zinc enriched implants to give long-term correction of zinc deficiency fails to sufficiently correct low zinc problems; thus, leading to consideration of a new approach involving banding with fine textured zinc enriched rubber as a slow release zinc form as a long-lasting solution. Additionally, special isotopically labeled zinc is being developed to enable determination of how foliar zinc is moving within trees; thus, potentially providing a better and cheaper means of controlling tree zinc nutrition.

Scab disease: Field studies on the roles of nickel (Ni) and phosphite (PO3) for improving tree resistance to pecan scab disease found significant efficacy for both against scab disease; thus, leading to research integrating both into practical disease management strategies. The discovery of high concentrations of the rare-earth elements in foliage is suggestive that they play a biological role in disease resistance; thus, this possibility is being studied. Scab resistance: Several commercially available agents are in the process of being tested, on seedling trees under field conditions, for triggering pecan tree resistance to scab disease. Molecular biology based research is now enabling better understanding of critical life cycle traits and fungi variability characteristics that can potentially lead to improvement in disease management in orchards.

Systemically acquired resistance to scab: Several commercially available agents are in the process of being tested, on seedling trees under field conditions, for triggering pecan tree resistance to scab disease.

Scab resistance: Molecular biology based research is now enabling better understanding of critical life cycle traits and genetic variability of the scab pathogen that will contribute to improvements in disease management in orchards through optimal use of host resistance.

1. Regulation of flowering in pecan. The plant processes that regulate flowering in pecan has heretofore been a mystery, with the relative roles of plant hormones and energy reserves being unknown. ARS researchers at Byron, GA, discovered that development of female flowers is initially regulated by an interplay of at least four classes of hormones within the bud meristem environment during the previous growing season, and subsequently regulated by non structural carbohydrate reserves within that same environment the following spring. This results in a new theory explaining how flowering in pecan involves a three-phase process acting during the twelve months preceding the visual expression of female flowers. This identifies new research avenues for better understanding the specific physiological processes regulating flowering as well as enabling new opportunities for development of horticultural tools and strategies capable of on-farm regulation of flowering within pecan orchards.

2. A role for the micronutrient nickel to help reduce pecan scab in orchards. Pecan scab can cause severe yield loss when environmental conditions are conducive to epidemic development. Furthermore, resistance to certain fungicides used by pecan growers to control the disease demands an integrated approach to management of this disease. Field and in-vitro studies demonstrated a small but significant effect of foliarly applied nickel at reducing pecan scab. By optimizing nickel nutrition growers are better managing the pecan scab in orchards and are reducing associated crop loss.

3. Use of phosphite to manage pecan scab in orchards. Pecan scab can result in premature fruit-drop or reduced kernel quality. Emergence of scab resistance to certain classes of fungicides commonly used by pecan growers to control the disease provides compelling reason to identify novel chemistries with minimal environmental impact to use as alternatives. Field studies have confirmed that phosphite is highly efficacious for controlling scab in pecan orchards, and they are now registered for use on pecan. These are the first studies to demonstrate efficacy of phosphite on pecan scab; thus, as a consequence, phosphites are being substantially used in commercial pecan orchards to control scab.

4. Increasing nut yield with ReTain. Excessive fruit-drop greatly reduces orchard profitability with certain varieties and in certain years. ARS researchers at Byron, GA, found that a commercialized natural growth regulator product, AVG (ReTain), reduces premature drop of ‘Desirable’ fruit under field conditions; thus increasing yield in certain years. The research identifies ReTain as a useful horticultural tool for managing crop load on certain sensitive alternate bearing cultivars; thus, providing farmers with a new tool for managing fruit-drop and alternate bearing.

5. Regulation of Alternate Bearing in Pecan. Alternate bearing is a major biological problem in pecan production. ARS researchers at Byron, GA, discovered that certain commercially available plant growth regulators can be used to influence subsequent season flowering; thus, providing possible new tools for regulating alternate bearing and flowering in commercial pecan orchards. These finding enable pecan farmers to reduce over-cropping in heavy crop-load years and to increase cropping in otherwise low crop-load years.

6. Identification of rare earth elements as likely beneficial micronutrients in pecan. Insufficient understanding of the nutrient element requirements of pecan trees limits productivity and disease resistance. ARS researchers at Byron, GA, found that pecan and other hickory species accumulate relatively high concentrations of the rare earth elements, with the species possessing a duplicate set of chromosomes being especially high accumulators. These elements appear to enable species survival under relatively high stress conditions and appear to be beneficial, or perhaps even essential, nutrient elements that have heretofore been ignored in orchard nutrient management. This information will lead to improved nutrient management of orchards and will likely contribute to reduced use of fungicides and greater water use efficiency.

7. Improving accuracy and precision of pecan scab assessment. Pecan scab causes severe disease on fruit and leaves. Having an accurate, precise, repeatable and reproducible method to assess scab reduces error and improves the quality of data for comparing treatments, and thus ultimately the results on which management decisions are based. Development of a standard area diagram set aides scab disease assessment on fruit, which reduces error and variability in disease assessments.

Review Publications
Wood, B.W. 2011. Influence of aminoethoxyvinylglycine (AVG) on yield and quality of nut crops from a commercial pecan orchard. HortScience. 46(4):586-589.

Wood, B.W. 2011. Influence of plant bioregulators on pecan flowering and implications for regulation of pistillate flower initiation. HortScience. 46(6):870-877.

Last Modified: 7/12/2014
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