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Research Project: Management of the National Collection of Carya Genetic Resources and Associated Information

Location: Crop Germplasm Research

Title: Thermal treatment using microwave radiation for the phytosanitation of Xylella fastidiosa in pecan graftwood

item Hilton, Angelyn
item JEONG, MYUNGHWAN - Texas A&M University
item HSU, JUI-HUNG - Texas A&M University
item CAO, FAN - Texas A&M University
item CHOI, WOONGCHUL - Texas A&M University
item Wang, Xinwang
item YU, CHOONGHO - Texas A&M University
item JO, YOUNG-KI - Texas A&M University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2020
Publication Date: 1/20/2021
Citation: Hilton, A., Jeong, M., Hsu, J., Cao, F., Choi, W., Wang, X., Yu, C., Jo, Y. 2021. Thermal treatment using microwave radiation for the phytosanitation of Xylella fastidiosa in pecan graftwood. PLoS ONE. 16(1). Article e0244758.

Interpretive Summary: Pecan bacterial leaf scorch (PBLS) disease, caused by Xylella fastidiosa, is transmitted through nuts to seedlings, and then through xylem to leaves. Removal of PBLS bacteria from pecan scion wood is difficult. Currently, hot-water treatment (HWT) is only one proposed phytosanitary method to eliminate X. fastidiosa from pecan scion wood. This project developed a novel phytosanitary thermal treatment by using microwave radiation to reduce or eliminate X. fastidiosa from pecan scion wood. This technique simply heated carbon nanotubes (CNTs) by microwave radiation and significantly increased the efficiency of bacterium elimination, compared to hot water treatment.

Technical Abstract: Pecan bacterial leaf scorch, caused by Xylella fastidiosa, is an emerging disease for the U.S. and international pecan industries and can be transmitted from scion to rootstock via grafting. With the expanse of global transportation and trade networks, phytosanitation is critical for reducing the spread of economically significant pathogens, such as X. fastidiosa. We developed and evaluated thermal treatments using microwave radiation and microwave absorbers [sterile deionized water (dH2O) and carbon nanotubes (CNTs)] as novel disinfectant methods for remediating X. fastidiosa in pecan scions. Partial submergence of scions in dH2O or CNT solutions resulted in the transport of microwave absorbers in the xylem tissue via transpiration but did not compromise plant health. The microwave absorbers effectively transferred heat to the scion wood to reach the temperature range of 50-70C. Microwave radiation exposure for 6 sec (3 sec for two iterations) of CNT- or dH2O-treated scions reduced the frequency of X. fastidiosa- positive in pecan scions without negatively affecting plant viability when compared to the control group (dH2O-treated but no microwave). The efficacy of the new thermal treatments based on microwave irradiation was comparable to the conventional hot-water treatment (HWT) method, in which scions were submerged in 46C water for 30 min. Microwave irradiation can be employed to treat X. fastidiosa-infected scions where the conventional HWT treatment is not feasible. This study is the first report to demonstrate novel thermal treatment methods based on the microwave irradiation and microwave absorbers of dH2O and CNT as an application for the phytosanitation of xylem-inhabiting bacteria in graftwood.