Influence of Rootstock Ecotype on Physiological Responses and Survival of Avocado Trees to Flooding

Avocado (Persea americana Mill.) trees are classified into three ecotypes: Mexican (M), Guatemalan (G), and West Indian (WI) based on their geographical center of origin. In southern Florida, avocado trees are grown on WI seedling rootstocks, mainly ‘Waldin’, generally with WI or WI × G hybrid scions. Flood tolerance is influenced by the rootstock, and ‘Waldin’ seedling rootstock is sensitive to short-term flooding. However, effects of rootstock ecotype on flood tolerance have not been reported. This study compared responses of a WI avocado scion (‘Simmonds’) among clonal avocado rootstocks of each ecotype. ‘Simmonds’ was grafted onto clonally propagated ‘Duke 7’ (M), ‘Reed’ (G), or ‘Waldin’ (WI) rootstocks and subjected to either short-term (1.5 days) of flooding or not flooded (control). As an indicator of plant stress, leaf gas exchange [net CO2 assimilation (A), stomatal conductance (gs), transpiration (Tr), and water use efficiency (WUE)] was measured during the flooding period and after trees were unflooded until flooded plants lost too many leaves to measure. After new leaves emerged on defoliated trees, leaf gas exchange was measured, and trees were harvested for dry weight determination. Flooding reduced leaf gas exchange and leaf dry weight of trees on clonal M or G rootstocks, but not on the clonal WI rootstock. All trees on the clonal WI rootstock survived flooding, whereas 87% of trees on clonal M and 50% of trees on clonal G rootstock survived flooding.