Zinc-deficiency of Hevea brasiliensis as a Predisposing Factor to Oidium Infection

Abstract

INFECTION of the Hevea rubber tree by Oidium heveae is common in Malaya but is not regarded as a major pathological problem; in Ceylon, however, the fungus can produce serious loss of crop yields and the problem is of economic importance¹. Oidium heveae is most prominent in Malaya at the time of refoliation after ‘wintering’ of the trees, when it may cause a secondary leaf-fall. It is only at this time that Oidium is found on leaves exposed to full sun. Throughout the year it may be found on young plants but only when these are shaded, and then never sufficiently seriously to cause defoliation. A small number of poorly developed colonies of Oidium heveae are usual on the leaves of plants grown in our plant-house² as the glass and framework of the house provide light shade. During the study of the micro-nutrient-deficiency symptoms of Hevea brasiliensis grown in sand culture within this house, a striking relationship between the susceptibility to severe Oidium heveae attack and the zinc status of the plants was noticed. This relationship was not noted for the copper- or molybdenum-deficient plants grown simultaneously and in the same environmental conditions as the zinc-deficient plants. Our observations were thus made on plants grown under glass and were derived from one experiment only; the results, however, were so well marked that their significance should be quickly tested and evaluated in countries where Oidium heveae attack is of major concern.