Development and validation of severity scales of avocado wilt complex caused by Phytophthora cinnamomi, Verticillium dahliae and hypoxia-anoxia disorder and their physiological responses in avocado plants

Abstract

Avocado wilt complex (AWC) is the most important disease in this crop. AWC may be caused by different causal agents that induce similar symptoms. Accurate scales of disease development (SDD) and physiological changes may be of special importance for the diagnosis and management of AWC. The objective of this work was to design and calibrate a specific SDD for the most common causal agents associated with AWC in Colombia, Phytophthora cinnamomi Rands and Verticillium dahliae Klebahn, and the hypoxia-anoxia disorder in both seedlings in net house and adult plants under field conditions. Furthermore, physiological responses to infection were determined. The disease was monitored under field and net house conditions. Shoot symptoms were recorded and quantification of inoculum in infected soil and tissue was performed. The visual scale was described based on external symptoms and calibrated with the inocula values by regression analysis. In the net house, net photosynthesis, stomatal conductance, and transpiration were measured during the different stages of disease development. The three causal agents induced a progressive reduction of net photosynthesis, stomatal conductance, and transpiration. The designed scales can be a valuable tool for epidemiological use and support in the diagnosis and management of AWC.

Keywords

• epidemiological analysis
• disease measurement
• severity calibration
• inoculum
• disease management