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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Research Project #436942

Research Project: Evaluating the Physiological Responses of Superior Juglans Germplasm to Drought Stress

Location: Crops Pathology and Genetics Research

Project Number: 2032-21220-008-019-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Aug 1, 2019
End Date: Jul 1, 2023

Determine resistance to water deficit across superior genotypes of Juglans germplasm preselected for disease/pest resistance.

We will evaluate drought-induced water stress tolerance of elites with known pathogen responses: AX1 (J. californica X J. regia); RX1 (J. microcarpa X J. regia); VX211 (J. hindsii X J. regia); paradox hybrid; own-rooted Chandler, and two elites of (J. microcarpa X J. regia) as own-rooted (i.e. non-grafted) trees and as rootstocks with a common scion J. regia ‘Chandler’ in both greenhouse and field conditions. In the greenhouse, saplings will be planted to large pots filled with autoclaved sandy loam soil in consideration of the water holding capacity. Plants will be subjected to gradual drydown events determined as a % of full ET based on diurnal weight loss measured on bagged pots from the fully hydrated treatment. Water stress treatments of 60 and 30% ET will be achieved with gradual step-wise reduction in water application. In the second summer, the above watering treatments will be repeated but using own-rooted and grafted materials for the best performing accessions. Recovery from water stress will also be assessed at the end of each drydown cycle. A small subset of genotypes will be planted under field conditions to validate results from the greenhouse tests under field conditions. The plantings cross link with the spectral phenotyping applications of (iii). Plant responses to water stress treatments will be tracked with water potential (leaf, stem, and predawn), transpiration rates and stomatal conductance. Plant growth will be characterized throughout the studies using a combination of non-invasive and destructive sampling. Repeatedly, daily water loss from every pot will be measured by weighing bagged pots at predawn and at the end of the day, and will be combined with water potential measurements to calculate hydraulic conductivity (K) using an evaporative flux method (i.e. K= daily water loss ÷ [midday – predawn]). MicroCT will be used to evaluate xylem pit characteristics for dried materials of each accession. The role of fine root K plays in altering water uptake capacity using methods of Cuneo et al. (2016)will be determined, and the role of ABA accumulation in preventing the recovery of stomatal conductance after a simulated irrigation event will be assessed. At the end of all experiments, plants will be destructively harvested and analyzed for biomass allocation. A field experiment will be conducted with own-rooted J. regia ‘Chandler’ and as a common scion on two rootstock genotypes of a cross of J. microcarpa 29.11 X J. regia ‘Serr’ planted to field plots at the Kearney Ag Center in factorial split-split plot designwith two levels of watering regime (100% ET, 60% ET) and two levels of nematode infestation (non-inoculated, inoculated with P. vulnus). Similar physiological and growth measurements to those described above will be taken under these conditions, and also serve as validation for spectral phenotyping efforts.