A Virus Technique Useful to Diagnose Foliar Deficiencies.

Plants of Coffea dewevrei De Wild. et Th. Durant var. excelsa Chev. growing in nursery beds in a lath house at the Instituto Agronomico, Campinas, Brazil, exhibit frequently a type of chlorosis in the leaves (1). Repeated attempts were made to improve the condition of the chlorotic plants by spraying their leaves with salt solutions of various elements, including iron, zinc, manganese, magnesium, etc. None of these treatments induced recovery of the normal green color, but it was noticed that some leaves of the plants sprayed with ferrous sulphate showed a few small islands of green tissue. The examination of these green areas revealed that they usually surrounded a point at which the leaf had been injured. This observation was suggestive that the chlorosis might be the result of iron deficiency in the leaves, and that the penetration of the iron solution in the tissues occurred only in the vicinity of points where the leaf had been injured. Since a slight injury of the leaf was apparently beneficial for the penetration of the iron solutions in the leaves of the chlorotic coffee plants, it occurred to the writers that the use of carborundum as an abrasive (2) and the half-leaf technique might be good methods to be employed for the diagnosis of foliar deficiencies. The results obtained with this technique in the study of the cholorosis of the coffee plant were very satisfactory and indicate that its application might be useful also in leaf deficiencies of other plants.