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.

Sound absorption property of wood for five eucalypt species

The sound absorption coefficients of wood and wood boards for five eucalypt species (Eucalyptus urophylla, Euca-lyptus urophylla E. grandis, Eucalyptus urophylla E. tereticornis, Eucalyptus urophylla E. camaldulensis and Eucalyptus cloeziana) that were collected from plantation in Dongmen Forestry Center of Guangxi Province, China were tested with stand-ing wave method and their sound absorption properties were also compared. The results showed that the sound absorption co-efficients of the five eucalypt wood species did not change evidently below 1000 Hz, but above 1000 Hz their sound absorption coefficients increased with the increasing frequency. The difference in sound absorption coefficient among five species of eucalypt wood is not evident at the tested frequency range (200-2000 Hz), but the sound absorption property of Eucalyptus urophylla at low frequency is better than that of other four species. The sound absorption coefficient of the tangential-sawn board is higher than that of the radial-sawn board. The sound absorption property of eucalypt wood of 0.5 cm in thickness is much better than that of 1.0 cm in thickness. It is concluded that wood sound absorption properties of eucalypts are affected by their board thickness and the type of sawn timber within the testing frequency, but the variance of wood sound absorption property among the five tested species is not significant.

Solid Wood Products from Eucalypts Plantations

To improve and diversify the use of tropical plantation timbers in Southern China, with support from International Tropical Timber Organizations (ITTO), a research project was started in 2002 focusing on development of processing and manufacturing technologies to promote production of value-added wood products from eucalypts plantations. This project will also facilitate the formulation of forest management strategy in China to supplement the diminishing supply of timber from the natural forests. The sp...