Infectious Diseases of Trees Associated with Water and Freezing Stress

Abstract

Studies on the susceptibility of water-stressed, container-grown deciduoustrees to inoculation with Botryosphaeria dothidea showed that a thresholdlevel of plant water potential of c. -12 to -13 bars was necessarybefore stems became susceptible to attack. Less severely stressedplants remained resistant for >3 wk, while cankers appeared within5 days on severely stressed plants. Container-grown plants in whichstems were subject to freezing stress were predisposed to infectionby various weak pathogens (B. dothidea, Tubercularia ulmea and Nectriacinnabarina) at threshold temps. between -20 and -30 deg C. All remainedresistant at temps. of -20 deg or above. It was concluded that theweak pathogens should be regarded as a vital part of the complexof factors resulting in damage in plants subjected to environmentalstress.