Physiological responses of seedlings to the invasion of brown root rot hyphae differ between semi-deciduous Bischofia javanica Blume and evergreen Rhaphiolepis umbellata (Thunb.) Makino

Brown root rot, caused by infection of the basidiomycete Phellinus noxius (Corner) G. Cunn., threatens many tree species in forests, orchards, and plantations of tropical regions. However, the precise physiological impairment of the trees with disease progression remains inadequately understood. Here, we chronicle the root decay, water relation, and physiological traits of leaves using artificially inoculated seedlings of two tree species of different leafing habits, semi-deciduous Bischofia javanica Blume and evergreen Rhaphiolepis umbellata (Thunb.) Makino. Stomatal closure seemed to be the primary reaction, without either species exhibiting a decrease in root hydraulic conductance associated with hyphae invasion or change in stem water potential. Compared with R. umbellata, B. javanica with highly sensitive stomatal response, alleviated the deterioration in carboxylation from hyphae invasion by thermal dissipation of excessive energy. These physiological responses were detected earlier than the appearance of visible disease symptoms. Although there were some differences in chlorophyll fluorescence (ChlF) response between the two species, our results have demonstrated that decreases in stomatal conductance and changes in ChlF, possibly depending on the species' leafing habit are some of the initial physiological responses of trees during the early phase of brown root rot infection.