Sensitivity and variability of two plant water stress indicators: exploring criteria for choosing a plant monitoring method for avocado irrigation management.

Jose M. Celedon1, Pilar M. Gil2, Raúl Ferreyra3*, Patricio Maldonado3, Cristian Barrera1

Avocado (Persea americana Mill.) is a fruit-tree species highly susceptible to water deficiency, which makes irrigation management a difficult task for growers. When irrigation is inadequate, trees suffer growth reduction, fruit losses, and roots damage. This study addressed the question of how to assess water stress in avocado trees and the considerations to choose an indicator to measure the plant water stress. In this work the sensitivity and variability of two water stress indicators in response to water deficit were analyzed: stem water potential (SWP) and midday trunk shrinkage (MDTS). During a period of high water demand, avocado trees planted in a clay loam soil were subjected to water stress by withholding irrigation and compared to control trees irrigated according to the maximal crop evapotranspiration. During the study, avocado trees reached a minimum SWP of -0.9 MPa and a maximum MDTS of ~ 285 µm. To better understand avocado tree response to water deficit, leaf abscisic acid, stomatal conductance, soil moisture, and vapor pressure deficit were also measured. Interestingly, it was found that water stress indicators showed differences with control after 3 d of withholding irrigation. It was possible to observe that MDTS was more sensitive in detecting water stress than SWP, signal strength of 4.5 vs. 1.2 respectively; however, MDTS higher variability counteracted its performance as stress indicator, coefficient of variation of 32% vs. 9%, respectively. This study confirms that monitoring water stress is an important tool for avocado irrigation management and should consider both, the sensitivity and variability of the indicator.

Keywords: Dendrometers, stem water potential, environmental stress, Persea americana.
1University of British Columbia, Michael Smith Laboratories, 2185 East Mall, Vancouver, BC V6T 1Z4, Canada.
2Pontificia Universidad Católica de Chile, Facultad de Agronomía e Ingeniería Forestal, Casilla 306-22, Santiago, Chile.
3Instituto de Investigaciones Agropecuarias INIA, Chorrillos 86, Casilla postal 3, La Cruz, Chile.*Corresponding author (rferreyr@inia.cl).