Armillaria Infection and Water Stress Influence Gas-exchange Properties of Mediterranean Trees

Abstract

The effect of inoculating seedlings of Mediterranean cultivated trees grown under greenhouse conditions with North American isolates of Armillaria mellea (Vahl: Fr) Kumm. and A. ostoyae (Romagn.) Herink on net photosynthesis (A), stomatal conductance (g s ), and water potential was examined. The effect of water stress was determined also on the same plant species independently and in combination with Armillaria infection. Red oak ( Quercus rubra L.) was used as a control to indicate Armillaria virulence on North American trees. Carob ( Ceratonia siliqua L.) was resistant to infection. Infection was successful in sour orange ( Citrus aurantium L.), but A, g s , and water potential were unchanged over the 60-day experiment. In olive ( Olea europea L.) and oak, A and g s were reduced following inoculation with A. mellea. A and g s of all species but carob were reduced under water stress. Olive and oak responses to water stress and Armillaria infection were quantitatively similar; however, the two stresses combined did not reduce A and g s further. Red oak was strongly susceptible to A. ostoyae infection, but Mediterranean trees were not infected by the same Armillaria isolate. Our results show that Armillaria infection may reduce A and g s in susceptible species.