Location: Fruit and Tree Nut Research
Project Number: 6042-21220-014-008-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Oct 1, 2022
End Date: Sep 14, 2025
Objective:
The genetic tools that were developed during USDA-National Institute of Food and Agriculture-Standard Research and Extension Project Grant #2016-51181-25408 will be utilized in this project to define and refine genetic markers that will benefit pecan growers by selection of appropriate pecan genotypes for specific regions and climates. Selection of pecan crop characteristics will improve by decreasing the time of pecan breeding and selecting desirable traits. Many of these traits exist in native pecan trees and related hickories that span the geographical region of North America. This effort focuses on novel phenotyping methods and collecting necessary datasets that capture this variation into horticulturally viable cultivars using tools like marker assisted selection and genomic prediction. These new pecan cultivars and rootstocks will improve crop characteristics by their selection with desired traits that will increase nutritional value of pecans. These genotypic traits will benefit the environment as we decrease our water and pesticide use. These will be economically beneficial to growers as they will be able to produce a more stable crop with less inputs, processors as they will have a stable crop from year to year and ultimately consumers as there will be a more stabilized pricing for nutritionally beneficial pecan nuts.
Specific Objectives:
1. Understand genetics and develop markers for climate adaptation of pecan trees for traits in both scions and rootstocks associated with climate. Key traits include vivipary (pre-germination), bud-break timing, and dormant season hardiness (freeze injury). This includes the genetics and screening rootstocks and scions and that are optimal for specific soils and climates.
2. Develop genomic selection of rootstocks and scions to improve water use efficiency with salinity and drought tolerance.
3. Develop markers for breeding resistance to fungal and bacterial organisms and insects, and identify useful genes for these traits.
4. Determine genetics to elucidate the gene networks that control nut size, nutrition, and pecan flowering phenology to mitigate alternate bearing.
5. Determine genetics that control canopy size, density, and structure.
6. Assay potential pecan allergen proteins against nut-feeding insect pests.
7. Evaluate selected pecan germplasm for susceptibility to pecan aphid species.
Approach:
Pecan biological interactions. Diseases caused by fungal and bacterial organisms and insect damage presents enormous challenges to pecan growers. Scab is caused by a fungal organism called Venturia effusa and causes major production loss and pesticide inputs for pecan growers in the Eastern US. Mapping populations (‘Lakota’ x 87Mx), (‘Pawnee’ x ‘Elliott’) (‘Kanza’ x ‘Pawnee’) have been developed and initial observations indicate that resistance to scab is segregating. Scab isolates that have been collected will be used to evaluate resistance in these mapping populations. RNA-Seq studies will be used to determine defense genes that are involved in resistance. Pecan bacterial leaf scorch is an issue in both the Eastern and Western US and was found to be endemic in Georgia. We will evaluate the observed differential symptom development in pecan cultivars with the presence of Xylella fastidiosa subspecies. Specific pecan genomes display resistance to aphids, we will determine the genetic mechanism behind this resistance for breeding. The pecan microbiome will be determined in different pecan trees/in geographical location by next generation sequencing and its impact on pecan health will be studied.
Gene networks and markers that control flowering, nut size and nutrition will be experimentally evaluated. We will continue to elucidate the gene networks that control pecan flowering phenology for the mitigation of alternate bearing and study genetics of pecan nut size, shape, nutrition and allergens.
Pecan tree architecture and horticultural issues. We will begin to examine the genetics that underpin the limb angles and tree height. Differences in tree architecture is apparent from pecan trees that originated in warmer areas (Mexico) compared to trees that originated in the northern US. Trees from Mexico show a more indeterminate growth patterns as compared to northern trees. Size control is desired, and we will evaluate pecans and Carya for the genetics of tree height. We will continue to elucidate the gene networks that control pecan flowering phenology for the mitigation of the impacts of alternate bearing and genetics for pecan nut nutrition and allergens
