Net Gas Exchange as a Damage Indicator for Phytophthora Root Rot of Flooded and Nonflooded Avocado

Net CO 2 assimilation (A) and stomatal conductance for CO 2 (g s ) were determined for flooded and nonflooded avocado plants ( Persea americana Mill .) with different severities of phytophthora root rot (caused by Phytophthora cinnamomi Rands). Under nonflooded conditions, root necrosis (primarily due to P. cinnamomi) of <50% generally had little effect on net gas exchange, whereas root necrosis ≥50% resulted in decreases in A and g s of up to 65% when compared to noninfested controls. However, root necrosis ≥20% greatly reduced A and g s when plants were flooded for 7 days. Net CO 2 assimilation and g s were not reduced when plants without root rot were flooded for 7 days.