RESIN YIELD AND TIMBER QUALITY OF Pinus caribaea TREES TAPPED USING RILL METHOD

Experiments to study the oleo-resin yield in different diameter trees, tapping depths andtapping heights were under taken in the wet zone in the Kalutara District. Oleo-resin yieldwas measured in Pinus caribaea trees belonging to two diameter classes (10 em - 20 cmDBH, >20 cm DBH classes), two tapping heights above ground (0.5 m and 1.3 m) andthree tapping depths (I mm, 2 mm and 5 mm).Results showed that oleo-resin yield was higher in larger diameter classes compared withlower diameter classes. Resin yield was also higher at 1.3m tapping height compared with0.5m height. Resin yield also increased as the tapping depth increased from I mm to 5mm. Based on these data it is recommended that the lowest tappable limit may be above20 ern DBH and it can expected to increase the yield of oleo-resin as well as health andvigour of the tree. It is suggested the height of tapping should be increased to yield moreoleo-resin. However the cost of tapping would increase when higher heights are to be used.A 5 mm depth starting from the live bark can be recommended as suitable depth in resintapping. This depth can increase the yield of oleo-resin while maintaining the health andvigour of the tree.Experiments to study the growth rate and timber quality of tapped and untapped P.caribaea trees were also done by measuring density and width of the rings. Log samplesfor this experiment were obtained from plantation at Guruthalawa in the Badulla district.At the time of sampling these trees had been tapped for 5 years.There were three tapped and three untapped trees which belonged to 3 diameter classes(20cm, 28cm, 36.5 ern). Each couple of tapped and untapped tree had the same diameter.For each tree, discs were extracted at 0.5 m height and 1.3 m height. The width of growthrings which is a measure of growth rate, were measured on untapped tree, tapped radiusand untapped radius in tapped tree. The data showed that wood production has not beenaffected considerably by resin tapping.The density which is an indicator for wood quality showed an increasing trend from pithoutwards. Density in the tapped trees was higher due to infiltration of oleo-resin into thewood after resin tapping. Except this variation, no other considerable difference wasobserved in density between tapped and untapped trees.

Plasmodesmata: Channels for Viruses on the Move

The symplastic communication network established by plasmodesmata (PD) and connected phloem provides an essential pathway for spatiotemporal intercellular signaling in plant development but is also exploited by viruses for moving their genomes between cells in order to infect plants systemically. Virus movement depends on virus-encoded movement proteins (MPs) that target PD and therefore represent important keys to the cellular mechanisms underlying the intercellular trafficking of viruses and other macromolecules. Viruses and their MPs have evolved different mechanisms for intracellular transport and interaction with PD. Some viruses move from cell to cell by interacting with cellular mechanisms that control the size exclusion limit of PD whereas other viruses alter the PD architecture through assembly of specialized transport structures within the channel. Some viruses move between cells in the form of assembled virus particles whereas other viruses may interact with nucleic acid transport mechanisms to move their genomes in a non-encapsidated form. Moreover, whereas several viruses rely on the secretory pathway to target PD, other viruses interact with the cortical endoplasmic reticulum and associated cytoskeleton to spread infection. This chapter provides an introduction into viruses and their role in studying the diverse cellular mechanisms involved in intercellular PD-mediated macromolecular trafficking