SEED-BORNE FUNGAL CONTAMINATION - CONSEQUENCES IN SPACE-GROWN WHEAT

Plants grown in microgravity are subject to many environmental stresse s that may promote microbial growth and result in disease symptoms. Wh eat (cv. Super Dwarf) recovered from an 8-day mission aboard a NASA (N ational Aeronautics and Space Administration) space shuttle showed dis ease symptoms, including girdling of leaf sheaths and chlorosis and ne crosis of leaf and root tissues. A Neotyphodium species was isolated f rom the seed and leaf sheaths of symptomatic wheat used in the spacefl ight mission. Certain isozymes of a peroxidase unique to extracts from the microgravity-grown plants were observed in extracts from earth-gr own Neotyphodium-infected plants but were not present in noninfected w heat. The endophytic fungus was eliminated from the wheat seed by prol onged heat treatment at 50 degrees C followed by washes with water at 50 degrees C. Plants from wheat seed infected with the Neotyphadium en dophyte were symptomless when grown under greenhouse conditions, where as symptoms appeared after only 4 days of growth in closed containers. Disease spread from an infected plant to noninfected plants in closed containers. Dispersion via spores was found on asymptomatic plants at distances of 7 to 18 cm from infected plants. The size and shape of t he conidia, my celia, and phialide-bearing structures and the ability to grow rapidly on carbohydrates, especially xylose, resembled the cha racteristics of N. chilense, which is pathogenic on orchard grass, Dac tylis glomerata. The Neotyphodium wheat isolate caused disease symptom s on other cereals (wheat cv. Malcolm, orchard grass, barley, and maiz e) grown in closed containers.