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It is generally recognized that the susceptibility and prevalence of manv plant diseases are associated with plant nutrition. The peanut plant is susceptible to leafspot infection which becomes economicallv important during the last half of its growth period when the crop is planted in the spring. The severity and rapid spread of infection in the field may not be due to the mere presence of the organism, which is ubiquitous, but to the susceptibility of plants suffering from improper niutrition in certain stages of their growth. Results herein reported of a nutritionial study with the Dixie Runner variety of peanut support this assumption.The experimental peanut plants were grown in sand culture with the roots of each plant in a single gallon glass jug which completely isolated the roots from the fruiting or pegring zone of the plant ( fig. 1). The nutrients were applied to the rooting medium by the continuous flow miiethod of SHIVE and STAHL (6), while the nutrients on the pegging zone were applied on the surface and by feedingo through the base of the box. For 75 days after germination the rootino and fruiting zones of all cultuires were supplied HOAGLAND'S (4) no. 1 complete nutrient solution modified by reducing the concentration of the macronutrienits by half and the microniutrients to onetenth. Ferrous iron was added as needed. At the enid of that period the following nutrient treatments were begun on the rootinog medium: complete, ininus phosphorus, minus potassiumii, minus calciumii, inus magnesium, minus sulphur, and minus Inieronutrient elements. The complete nutrient solution was applied to the fruiting medium throuohout the experiment.There were three replicates of single plants to each treatment and the roots of each culture received 1.5 liters of nutrielnt solution daily; the pegging region received 3.5 liters of solution weekly. Plants were grown 21 days in the greenhouse after germination alnd then because of high temperature were moved outside under a framiie cov-ered with one thickness of cheesecloth. This report will deal only with the results obtained with the magnesium-deficient cultures, sinee these plants were the only ones that developed the leafspot disease to any appreciable extent uinder the conditions of this experiment.The leaves of the minus-magnesium plants showed interveinal chlorotic centers with green margins 24 days after magnesiumi was withheld from the roots. However, the effect appeared initially on the first leaf below the growing tip of the oldest branches. This is in eontrast to the typical magnesium deficieney on other plants which usually ocecurs first on the basal 237 www.plantphysiol.org on May 9, 2018 -Published by Downloaded from

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