Reduced lysine uptake by bean rust haustoria in a resistant reaction

tern) and a common pathogen of the pumpkin, the fungus Sclerotinia sclerotiorum (Lib.) de Bary, were the organisms selected. Magnesium and manganese were chosen since both ions are important in plant metabolism [4], especially photosynthesis [5], and are also interchangeable as co-factors for malay biochemical reactions. The pumpkin seedlings were germinated (98% germination after 5 days) on paper towels and grown in trays of acid-washed quartz sand in a growth chamber adjusted for 16-h days at 30~ and 21~ nights. Plants were grown under polyethylene humidity-control chambers which were made by cutting the bottoms from 5-1 polyethylene reagent bottles. They maintained high humidity around the plants and also prevented cross-contamination between t reatments-an important consideration for working with an infectious disease. The polyethylene was translucent and allowed good temperature equilibration as well. Four pumpkin seedlings were put under each polyethylene chamber. Four chambers were set in each of six trays. Thus for each treatment (complete, minus Mg, or minus Mn) there were 4 plants not inoculated and 28 plants inoculated with the pathogen. The pumpkin seedlings were watered daily with Hoagland's solution, either complete or minus magnesium or minus manganese. Sclerotia of the fungus were supplied by Duane Letourneau (University of Idaho, USA). Cultures of the fungus were obtained by growing