A. P. Singh

Vestured pits of the tracheary elements in the petiolar xylem of Eucalyptus delegatensis had moderately developed vestures which extend into the pit chamber from bordering walls. Tubular structures were found in abundance in those pit membranes which underwent extensive hydrolysis of their matrix substances.

A.L. SINGH and P.K. SINGH

Rice fields were inoculated with four isolates of Azolla pinnata R. Br. from Thailand, Bangladesh, Vietnam, and India as well as with fresh or dry blue-green algae (BGA). Increments in biomass and N yield of Azolla and BGA were compared, and their effects on rice yields and yield components were studied. Inoculation of Azolla (500 kg fresh weight/ha) 10 days after rice transplanting (DAT) and of BGA (10 kg/ha dry and 100 kg/ha fresh) 3 DAT yielded maximum biofertilizer biomass at 30 and 80 DAT, respectively. The establishment of BGA in the rice field was faster and the biomass and N yield were initially higher in the case of the fresh than in that of the dry inoculum. At the flowering stage (80 DAT), however, these parameters were similar with both inocula. Azolla isolates grew more rapidly than BGA and produced a mat on the water surface 30 DAT. The relative growth rates of the Thailand and Vietnam Azolla isolates were higher than those of the Bangladesh and Indian isolates. Significant increases in tiller numbers, plant height, panicle number, panicle weight, grain and straw yields, total dry matter, and N uptake were observed in dual cropping with Azolla and BGA. Grain and N yields in the plots treated with Azolla and BGA were comparable to those obtained following application of 30 kg N/ha as urea. Straw yield in BGA dual cropping was significantly lower than after application of 30 kg N/ha as urea or after Azolla treatments. The 4 Azolla isolates did not differ as to their effects on rice grain and straw yields.

L. A. Donaldson and A. P. Singh

A sample of Terminalia wood recovered from an ancient Polynesian canoe thought to be approximately 1000 years old, was examined by light and electron microscopy to determine the extent and pattern of degradation. A chemical analysis was also carried out. The secondary walls of fibres, vessels and parenchyma cells were extensively degraded but the compound middle lamella remained relatively intact. Vestures in intervascular pits were preserved, presumably by virtue of their high lignin concentration. Plasmodesmata were also preserved by infiltration with extractives thought to be tannins.

A. P. Singh, T. Nilsson and G. F. Daniel

Electron microscopic examination of vessels and fibre-tracheids of Alstonia scholaris exposed to tunneIIing bacteria (TB) in liquid cuItures showed degradation of aU areas of the secondary waU incIuding the highly lignified middle lameUa in advanced stages of attack. However, vestured pit membranes and vestures appeared to be resistant to degradation by TB even when aU other waU areas in A. scholaris wood ceIIs were severely degraded. The size comparison indicated vestures to be considerably smaIIer than TB, and we suspect that this may be the primary reason why vestures in A. scholaris wood were resistant to degradation.

A.P. Singh, M.E. Hedley, D.R. Page, C.S. Han and K. Atisongkroh

Transmission electron microscopy of decaying CCA-treated Pinus radiata timbers from an industrial water cooling tower showed the presence of a thick biofilm covering some areas of the wood. The biofilm contained various morphologically distinct forms of microorganisms embedded in a slime. The study provided evidence of the activity of soft rot fungi and tunnelling and erosion bacteria in wood cells covered by the biofilm. The extent of microbial damage to wood cells varied, with combined fungal and bacterial attack having the most damaging impact.

Adya P. Singh, Yoon Soo Kim and Ramesh R. Chavan

Edited by Lloyd A. Donaldson

ABSTRACT

This review presents information on the relationship of ultrastructure and composition of wood cell walls, in order to understand how wood degrading bacteria utilise cell wall components for their nutrition. A brief outline of the structure and composition of plant cell walls and the degradation patterns associated with bacterial degradation of wood cell walls precedes the description of the relationship of cell wall micro- and ultrastructure to bacterial degradation of the cell wall. The main topics covered are cell wall structure and composition, patterns of cell wall degradation by erosion and tunnelling bacteria, and the relationship of cell wall ultrastructure and composition to wood degradation by erosion and tunnelling bacteria. Finally, pertinent information from select recent studies employing molecular approaches to identify bacteria which can degrade lignin and other wood cell wall components is presented, and prospects for future investigations on wood degrading bacteria are explored.