Location: Crop Germplasm Research
Project Number: 3091-21000-046-017-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Apr 17, 2026
End Date: Apr 16, 2027
Objective:
1. Evaluate cold hardiness of three northern pecan cultivars (Pawnee, Maramec, and Kanza) and one southern cultivar (Elliott, control) grafted onto Giles rootstock.
2. Determine relationships between carbohydrate reserves (soluble sugars and starch) and freeze tolerance across seasonal injury stages.
3. Identify genes and potential molecular pathways associated with cold tolerance using transcriptomic analysis.
Approach:
Objective 1: Cold Hardiness Testing
Scions of four cultivars will be grafted onto 2.5-year-old Giles rootstocks in spring 2026. Cold hardiness will be evaluated in early October, mid-January, and mid-March using controlled freeze chamber tests with three freezing temperatures plus a 4 °C control. Four seedlings per cultivar per treatment will be used. Freeze injury will be assessed using electrolyte leakage, tetrazolium staining, and post-freeze regrowth evaluation.
Objective 2: Carbohydrate Analysis
Soluble sugar and starch contents will be quantified in stems of frozen seedlings, with unfrozen seedlings serving as controls. Carbohydrates will be measured using modified microplate-based colorimetric assays. Relationships between carbohydrate reserves and cold hardiness will be analyzed.
Objective 3: Transcriptomic Analysis
Bud tissues will be collected in October and March with samples held under one freezing treatment and the control. RNA will be extracted using a validated protocol, followed by RNA sequencing, differential gene expression analysis, and pathway identification. Selected genes will be validated using RT-qPCR.