AUTHOR=Silva Jefferson Rangel da , Boaretto Rodrigo Marcelli , Lavorenti Jéssica Aparecida Lara , dos Santos Bruna Castriani Ferreira , Coletta-Filho Helvecio Della , Mattos Dirceu 

TITLE=Effects of Deficit Irrigation and Huanglongbing on Sweet Orange Trees

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 12 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.731314

DOI=10.3389/fpls.2021.731314

ISSN=1664-462X

ABSTRACT=This study  addresses the interactive effects of deficit irrigation and huanglongbing (HLB) infection on physiological, biochemical and oxidative stress responses of sweet orange trees. We sought to answer: (i) What are the causes for the reduction in water uptake in HLB infected plants? (ii) Is water status of plants negatively affected by HLB infection? (iii) What are the key physiological traits impaired in HLB infected plants? and (iv) What conditions can mitigate both disease severity and physiological/biochemical impairments in HLB infected plants? Two water management treatments were applied for 11 weeks to one year-old-trees that were either healthy (HLB –) or infected with HLB (+) and grown in 12 L pots.  Half of the trees were fully-irrigated (FI) to saturation, whereas half were deficit-irrigated (DI) using 40% of the water required to saturate the substrate. Our results demonstrated that: reduced water uptake capacity in HLB+ plants was associated with reduced root growth, leaf area, stomatal conductance, and transpiration. Leaf water potential was not negatively affected by HLB infection. HLB increased leaf respiration rates (ca. 41%) and starch synthesis, down-regulated starch breakdown, blocked electron transport, improved oxidative stress and reduced leaf photosynthesis (ca. 57%) and photorespiration (ca. 57%). Deficit irrigation reduced both leaf respiration (ca. 45%) and accumulation of starch (ca. 53%) by increasing maltose (ca. 20%), sucrose, glucose and fructose contents in leaves, decreased bacteria population (ca. 9%) and triggered a series of protective measures against further impairments to the physiology and biochemistry of HLB infected plants. Such results provide a more complete physiological and biochemical overview of HLB infected plant which can guide future work to screen genetic tolerance to HLB as well as to improve management strategies under field orchards.