Respiratory changes in barley leaves produced by single colonies of powdery mildew

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Abstract
The amount and lateral distribution of respiratory changes inbarley tissues infectedby Erysiphe graminis were determined using Gregg micro-respirometers. Actual leaf samples were 1.1 mm square with oxygen uptake rates of 0.03 to 0.25 microliters/hour. Respiration of mildewed tissues taken from colony centers was 7-10 times that of healthy tissues. With mildew hyphae removed, oxygen uptake was only 2-3 times that of healthy tissue. These findings were confirmed using standard Warburg techniques on heavily infected leaf segments 2-3 cm long. Respiratory alterations at the centers of single mildew colonies were not detected until 6 days after inoculation. Thereafter a zone of enhanced respiration spread from the center at about 1 mm/day, eventually extending at least 2 mm beyond the mildew hyphae. This rapid spread occurred at a time of high respiration and heavy sporula-tion at colony centers.