Periods Of Low Moisture Research Articles

Influence of water stress on Verticillium wilt of yellow-poplar

The pathogenisis of Verticillium vascular disease was evaluated in root-inoculated yellow-poplar trees grown under favorable, periodically saturated and chronically low soil moisture levels. Verticillium was significantly more aggressive in host trees stressed by periods of low moisture than in host trees subjected to periods of flooding. At no time did inoculated, flooded trees exhibit typical Verticillium symptoms nor was pathogen reisolation obtained from the aboveground parts of these trees. In contrast, inoculated trees treated at favorable and low soil moisture levels incurred extensive pathogen colonization. Histological studies showed that the xylem vessels of petioles became occluded by fungus growth and a dark staining material at the time of first symptom expression. Additionally, macroscopic and microscopic observations of flooded trees indicated that acute injury occurred in the stem base and, under some conditions, the cortex in this region developed an aerenchyma induced by flooding.