BORON DEFICIENCY IN EUCALYPT PLANTATIONS IN CHINA

Boron deficiency is identified as one of the more important causes of poor stem form and malformed leaves in plantations of Eucalyptus globu lus in Yunnan Province, and of Eucalyptus grandis, Eucalyptus teretico rnis, and Eucalyptus urophylla in Guandong Province. Symptoms of B def iciency in E. globulus were rolled and malformed leaves, stem dieback, and a prostrate form. In E. urophylla, leaf margins became chlorotic then necrotic, leaves turned brittle and corky, shoots died back, and the upper stem nodes were enlarged supporting numerous short-lived axi llary shoots. In E. grandis, stem dieback was preceded by the basipeta l accumulation of anthocyanin in leaves. Boron-deficient E. tereticorn is leaves developed marginal and interveinal chlorosis and recurved ma rgins. Depressed foliar B concentrations were associated with visible symptoms. In E. globulus, the mean B concentration in young leaves of healthy trees was 31 mg/kg dry matter compared with 10 mg/kg in prostr ate trees. Symptoms did not appear in E. globulus trees supplied with B fertilizer at planting. Normal shoot growth was restored in E. uroph ylla by the addition of B to the soil.