Use of stem diameter variations for detecting the effects of pathogens on plant water status

Linear variable displacement transducer (LVDT) sensors were used on Cistus plants, noninoculated or inoculated with the pathogens Botryosphaeria stevensii and Hypoxylon mediterraneum, to determine the suitability of this method to detect the effects of the infection process. Control and H mediterraneum infected plants did not differ in either the maximum daily shrinkage or the daily evolution of stem diameter. However, the pathogenic effects of B stevensii were clearly detected. Daily increase in stem growth stopped 19 days after the plants were inoculated and before any noticeable external symptom. Maximum daily shrinkage occurred 5 weeks after inoculation when foliar chlorosis and stem cankers were visible and preceded the plant mortality. Stem contractions were related to the amount of daily solar radiation when stress caused by pathogens did not exist. This methodology can be useful in the study of disease development, especially for those pathogens that affect the plant-water relations.