Location: Crop Germplasm Research
Project Number: 3091-21000-046-005-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Mar 1, 2023
End Date: Feb 29, 2024
Objective:
Pecan Bacterial Leaf Scorch (PBLS) caused by Xylella fastidiosa (XF) is widespread in US growing regions (Hilton et al., 2017; Bock et al., 2018). PBLS causes premature defoliation and reduces nut yields in susceptible cultivars. Drought and sustained high temperatures throughout the growing season can increase tree stress and disease susceptibility (Sturrock et al., 2011;Hossain et al., 2018). It is expected that higher incidence of PBLS occurs in orchards experiencing drought and/or heat stress. Improved irrigation methods and/or the identification of drought/PBLS-resistant rootstocks will provide growers integrated pest management options when frequented with harsh climatic conditions.
Approach:
Seed from nine pecan cultivars including Cape Fear, Desirable, and Wichita were collected in Fall 2022. In 2023, 400 seed from each cultivar will be germinated in the greenhouse. A previous study has revealed high seed transmission rates of X. fastidiosa in pecan; however, influencing factors such as environmental conditions, strain or subspecies type, or pecan genotype, have yet to be identified. Thus, all germinated seedlings will first need to be verified for X. fastidiosa infection before assignment to test or control groups. This will be done through either PCR on either sap extracted from petiole tissue using a pressure bomb, or on carbon nanotubule mediated extraction from ground petiole tissue. Once seedlings have been classified as infected or not infected, test and control groups will be devised for the following study. In a controlled experiment, seedlings infected with X. fastidiosa by seed transmission grown in growth chambers will be treated with different combinations of temperature and watering conditions and compared to a control group. At least 40 seedlings of three different cultivar types will be tested under each condition and control treatment by the Cooperator under the guidance of an ARS scientist. Test groups of 3 month old seedlings will receive watering at 100%, 50%, 25%, and 10% field capacity as previously described, and grown in the control temperature (25°C) as well as additional groups grown in growth chambers at the following temperatures 32 and 38°C (Feil and Purcell, 2001; Choi et al., 2013). At the conclusion of the test, at least one petiole from each seedling will be sampled by the Cooperator and have its concentration of X. fastidiosa determined by quantitative real-time PCR, as previously described (Hilton, et al. 2020).
