Effects of water stress on chestnut blight

Abstract

A range of moisture stress was induced in American chestnut (Castaneadentata (Marsh.) Borkh.) stem segments by incubating them in chambers maintained at humidities of 100%, 90%, or 70% or by soaking their unsealed lower ends in water. Stems then were inoculated with mycelial discs or conidial suspensions of a virulent strain of the chestnut blight fungus (Cryphonectriaparasitica (Murr.) Barr, Ep 155 (American Type Culture Collection No. 38755)). Bark osmotic potential and relative turgidity were monitored on these stems during the development of chestnut blight cankers. Canker expansion was greatest on the stem segments that were lowest in bark osmotic potential (−1.8 MPa) and relative turgidity (56.3%), whereas expansion was least on those stems that were highest in bark osmotic potential (−1.1 MPa) and relative turgidity (68.4%). Water stress, however, had little effect on conidial infection of wounds on stems collected during the growing season, but fewer conidial inoculations of wounds were successful on water-stressed stems collected during the dormant season. Bark osmotic potential of living trees ranged from −0.8 to −2.0 MPa in monthly samplings during the year. Mycelial growth and conidial germination of C. parasitica generally was not affected at osmotic potentials above −2.0 MPa (see companion paper). These results indicate that canker expansion, but not necessarily canker initiation, is favored by water stress and that the effects of water stress are greater on the host than on the pathogen.