Bacterial Wilt and Boron Deficiency Stress： A New Disorder in Eucalypt Plantations in South China

INTRODUCTIONEucalypts are particularly sensitive to Boron (B)deficiency resulting in loss of crown vigour, shootdeath, poor stem form, and reduced wood quality.B deficiency is a major constraint to theproductivity of eucalypt plantations in many partsof Asia (Dell et al. 2001, 1994). The symptoms ofB deficiency are more severe during the dry seasonand thus mildly affected trees may partially recoverduring the following wet season. The sites withsandy soils derived from granite and sands…

Bacterial Wilt and Boron Deficiency Stress:A New Disorder in Eucalypt Plantations in South China

This paper reports on a new disorder that first appeared in eucalypt plantations in south China in2003. The plantations were destructively sampled near Leizhou, Yanxi, Kaiping and Gaoyao in September toDecember 2003. Whilst some 5% of 0.5 to 1.5 year-old Eucalyptus urophylla trees declined rapidly andexhibited symptoms of wilting, the majority of the affected trees declined slowly and exhibited two foliarsymptoms. Young leaves initially developed an interveinal chlorosis extending from the leaf margin inwardsto the midrib. Most leaves then developed pockets of necrotic tissue that became bleached but typically hadbrown margins. The former symptoms have been recognised as being caused by limited boron supply in soil,but the latter symptoms have not been previously observed in eucalypts in China. Inorganic analysisshowed that the leaves with the latter symptoms had deficient B concentrations whereas the leaves fromhealthy trees had adequate B concentrations. Bacterial wilt, Ralstonia solanacearum, was present at all siteswhere foliar symptoms and tree death were present. The root system of all trees with foliar chlorosis andnecrosis had signs of infection in some roots and attrition of lateral roots. The trunk and branches of therecently died trees and the trees with advanced leaf drop had discoloured xylem, which on cutting, oozedbacterial slime. Possible relationships between root damage caused by abiotic (e.g. typhoons, root damagefrom hand weeding) and biotic factors and reduced B uptake are discussed. Recommendations are made forreducing bacterial wilt disease and improving B management in fast-growing short-rotation eucalypt plantations.