No abstract

Root and butt rot of Cassia nodosa, Cassia fistula and Delonix regia is caused by Ganoderma lucidum. Ganoderma root and butt rot is a lethal disease on C. nodosa, C. fistula, and D. regia trees, and G. lucidum was identified as the causal organism of this disease. Susceptibility of these host trees was higher when infected at a young age. All infected trees regardless of the age died after 6-24 months from the appearance of the first sign of the disease. Of these three susceptible host species, C. fistula was the most susceptible host, dying six months after the first visible sign of the disease. Host preference of G. lucidum was demonstrated when new healthy C. nodosa, C. fistula or D. regia trees were infected while bypassing other tree species including species of Fabaceae family, which were growing in the close vicinity of the infected trees.

Escalating cost of production (COP) and inadequate supply of skilled harvesters are among the major issues that natural rubber industry face today. Low frequency harvesting (LFH) systems of which trees are tapped in a lesser frequency than once in two days, are considered to be one of the solutions to overcome these issues. With the focus given to expand rubber in drier climates, the present study was aimed to investigate on the yield response of LFH systems, viz. harvesting trees once in three (d3), four (d4) and six (d6) days in the intermediate zone (IZ) with the stimulation protocols developed for the wet zone (WZ). With the decrease in harvesting frequency in IZ, yield per tree per tapping (GTT) increased, however yield per tree per year (YPT) decreased. No such declines were observed in WZ. Stimulation had no negative impact on percentage dry rubber content in latex (%DRC) or incidence of Tapping Panel Dryness. Whilst only the S/2 d3 system is acceptable for IZ in the present form, stimulation protocols are to be revised in other LFH systems. Bark consumption was reduced significantly by LFH resulting in several long-term beneficial effects. Effect of stimulation on latex physiology is also discussed.

Harvesting rubber latex is rather labour intensive since trees are traditionally tapped half spiral, once in two days (S/2 d2) resulting in unnecessary waste of tree bark. High cost of production, shortage of harvesters and reduced economic lifespan are the key issues in rubber plantations related to harvesting. Low intensity harvesting (LIH) systems (i.e. either reduction in harvesting frequency and/or tapping cut length) of rubber appear to be a practical solution to these issues by bringing down the labour requirement and the cost of production. Of these, only the reduction in harvesting frequency has been tried in Sri Lanka. Hence, the present study was aimed to develop new LIH systems with shorter tapping cuts. This study comprised two stage stimulant (Ethephon) based field trials to evaluate a wide range of LIH systems. The overall yield given by traditional S/2 d2 was used as the standard in evaluation. Stimulation protocols of different harvesting systems were adjusted from time to time to achieve this standard. In addition, growth and physiological parameters of latex and the financial viability of the principal system were also assessed. Among the LIH systems tested, S/4 d3 (tapping quarter spiral once in three days) was successful in providing benefits, such as increase in both overall profits and harvesters' income and reduction in harvesting cost and overall cost of production. The overall bark consumption was also greatly reduced. Above all, it allows tapping the virgin bark of base panels for over 24 years. Popularization of this approach is proposed after large scale commercial testing.

Munronia pinnata (Wall). Theob is a valuable medicinal plant which is widely used in Ayurvedic medicine in Sri Lanka. Due to over exploitation and low percentage of seed germination of M. pinnata it has become necessary to adopt ex situ conservation methods via in vitro propagation techniques. The objectives of this study was mass propagation, greenhouse establishment and comparison of in vitro propagated plants with seed raised plants. Callus cultures were initiated from different explant types such as apical buds, nodal segments, petioles, petals and leaf discs in Murashige and Skoog (MS) medium supplemented with 1.1 mg L 1 2,4-dichlorophenoxy acetic acid (2,4-D) and 0.5 mg L 1 benzyl amino purine (BAP) at 25 ± 1°C in complete darkness. Leaf discs (6.0 mm) showed significantly higher calli production (mean fresh weight 0.167± 0.04 g) than other tested explants. The best growth regulator combination for callus initiation was 1.1 mg L" 1 2,4-D and 0.3 mg L" 1 BAP which produced a mean of 0.30 ± 0.06 g callus while other treatments produced lesser amount of callus. Leaf discs taken from first fully opened leafs, produced the highest amount of callus (0.06 ± 0.01 g) and a decreasing trend was observed with increased maturity of the leaf. Tissues along the midrib area have a higher potential to give high yield of callus. Shoot proliferation was higher (32.9 ± 2.2) in MS medium containing 3.0 mg L 1 naphthalene acetic acid (NAA) and 3.0 mg L 1 BAP. Light intensity at 3000 lx showed significantly higher number of shoots (33.4 ± 2.84) than other tested light intensities. Half MS minerals supplemented with 0.2 mg L" 1 indole acetic acid (IAA) was the most effective treatment for root induction (75%) with the highest mean root length (15.05 ± 0.5 mm) and 3.15 ± 0.03 of mean number of roots. A suitable potting mixture for acclimatization was determined using different ratios of compost and sand. Higher percentage of survival (60%) was achieved with compost: sand 1:3. When morphological features of seed raised plants were -compared with tissue cultured plants, mean height increment was higher in seed raised plants while mean number of leaves was higher in tissue cultured plants and branching habit was observed only in tissue cultured plants. A comparison of physiological parameters between the two types of plants showed that the rate of photosynthesis was higher in tissue cultured plants whereas stomatal resistance was higher in seed raised plants.