Comparison of litter decomposition rate constant for Yagirala and Horton

An estimation of rates of litter decomposition was carried out in two forest types; Yagirala Forest Reserve (FR) in the Low Country Wet Zone and Horton Plains natural forest (NF) in montane zone of Sri Lanka. Yagirala forest reserve was located between 6°21′ to 6°26′ north altitude and 80°6’to 80011’east longitude in the lowland wet climatic zone in Sri Lanka. Horton Plains natural forest was located between 6° 47′- 6° 50′ north latitude and 80° 46′- 80′ 51′ east longitude in mid country of Sri Lanka.

Three 300m line transects with three plots (100 m distance between 2 plots) were established in each forest. Litter decomposition rates were determined using the mixed species litter bags method. A total of 54 bags were placed in the both Forests (9 replicates for one plot). The experiment was conducted for a period of 8 months. The rates of decomposition of litter recorded during this were fitted to the exponential decay model proposed by Olson (1963).

x/x=e-kt

Where, x is the weight of litter remaining after time ‘t’, x0 is initial weight of litter and k is decomposition rate constant. Results revealed that the mean annual litter decomposition rate constant for moderately exploited Yagirala forest reserve was 2.19 year-1 while the value for Horton Plains natural forest was 1.35 year-1.Litter accumulation rates for Yagirala Forest is 668.86 tons ha-1 year-1, and this value for Horton Plains natural forest is equal to 226.54 ha-1 year-1. According to the results, it was clear that Yagirala forest reserve situated in the low country wet zone recorded higher litter decomposition rates compared with Horton Plains natural forest situated in the Montane zone of the country.

L A M C Amarasekara and D M S H K Ranasinghe
Department of Forestry and Environmental Science, University of Sri Jayewardenepura, Sri Lanka.

Assessment of soil erosion hazard of Victoria catchment area using GIS as a

Victoria reservoir is located at an elevation of 340 m to 440 m with a geographical position of 7° 15¢ to 7° 19¢ N and 80° 39¢ to 80° 48¢ E which has been constructed by damming the River Mahaweli at Victoria fall, in Sri Lanka in 1983. The reservoir storage capacity is 721.2 MCM and upstream dam site comprises 1338 km2 in the districts of Kandy, Nuwara-Eliya and Matale. The elevation of the catchment ranges from 340 m to 2100 m.

Soil erosion is a major water quality issue in the upland reservoirs. The objective of this paper is to analyze catchment issues contributing to soil erosion in the Victoria reservoir and to evaluate the soil erosion risk areas in the catchment. Study was carried out from 2002 to 2004.

Soil erosion occurs due to natural causes such as rain fall, rainfall runoff and wind, and due to human activities. Universal Soil Loss Equation ( RKLSCA = P ) introduced by Wischmeier and Smith in 1965 is a most widely used method for estimating soil erosion. This encounters detachment of soil particles and its transport by raindrops and surface runoff, which depends on the rainfall erosivity (R), erodibility of soil (K), slope length factor (LS), cover and management factor (C) and the support practice factor of the equation.

The data on erosivity points were interpolated with 50 m resolution grid cells. The erodibility value relevant to each soil group was entered into the attribute table, which was converted into grid cells with 50 m resolution, containing soil erodibility values. The Triangulated Irregular Network (TIN) was created by contour interpolating with 20 m interval, and grid cell was 50 m. Using TIN, slope percentages map was derived, which was used to obtain LS factor. The C factor values relevant to each landuse type were entered into the attribute table. The map was converted into grid cells with 50 m resolution, containing C factor values.

The soil erosion of the Victoria catchment was categorized into five erosion categories, namely; low, moderate, high, very high and extremely high, which extend within Kandy, Nuwara-Eliya and Matale districts. All categories were spread both in the left and right banks.

Extremely high erosion areas extend over 24.34km2 with a percentage of 1.82, Very high erosion areas extend over 121.24 km2 with a percentage of 9.06, High erosion areas extend over 302.91km2with a percentage of 22.63, Moderate erosion areas extend over 434.01km2 with a percentage of32.43 and low erosion area extends over 454.97 km2 with a percentage of 33.99. The results of mapanalysis were confirmed through field verifications. The soil erosion is high in the high slope regionsand in the areas where soil conservation methods are inadequate or poor.

In vitro callus induction of Spilanthes calva DC [Spilanthes acmella auct. nonL,.] (Maha Akmella)

Spilanthes calva DC. (Maha Akmella) is a valuable medicinal plant belongs to Family Asteraceae. It is widely used in indigenous medicine to treat toothache in most of the Asian countries. Not only it has anesthetic properties, but also contain secondary metabolites, with the insecticidal properties, which could be used as potential bio insecticide. This is an annual plant, which grows to a height about 30 cm. After flowering mother plant is dried off. Four to six weeks later seeds are germinated and new seedlings are produced. Viability of seeds loses within short period of time. Even though seeds are germinated percentage of germination is low (about 30%). Rooting of cuttings is also not possible. This is a limitation in using this valuable medicinal plant for commercial production. Therefore it is very important to develop a protocol for mass propagation through tissue culture and establishing cell cultures will be useful for large-scale chemical extraction in industrial purposes.

Leaf discs were used as explant for callus initiation. In order to identify the suitable maturity stage for callus initiation, leaves were harvested at different maturity stages i.e first, second and third fully opened leaf.

Leaves were washed with Dettolä soap and soaked in a solution of Teepolä for 5 minutes. After that leaves were washed with running tap water for 45 minutes. In order to surface sterilize. Leaves were washed with 10% Cloroxä (5.25% Sodium hypochlorite v/v) for 5 minutes and then with 70% alcohol for 30 seconds each followed by three successive washings in sterile distilled water. These operations were carried out inside the laminar airflow cabinet before inoculation. Basal media tested for the study were full strength MS (Murashige and Skoog, 1962) medium and ½ MS (both macro and micronutrients) medium. Media were supplemented with different concentrations (1.0 mgl-1 – 3.0 mgl-1) of BAP and 2,4-D. Cultures were incubated under complete dark at 25±1°C in the growth room.

Study conducted by Haw and Keng (2003) on the same species produced multiple shoots from axillary bud explants without inducing callus in MS medium supplemented with 2.0 mgL-1 BAP. In the present study, callusing was observed within 5 days of incubation in full strength MS medium supplemented with BAP and 2,4D. It took longer period to initiate callus when both macro and micro nutrients in the basal medium was lowered to half and the amount of callus produced was also very low even after 6th week of incubation. In order to observe the time taken to produce maximum amount callus fresh weight was measured after 2nd, 4th and 6th week of incubation. It was observed that maximum amount of callus was produced within 4 weeks in all explant types tested with a maximum of 0.88 g ± 0.23 in leaf discs obtained from first fully opened leaf.

In order to determine the best growth regulator combination for callus initiation, calli fresh weights were measured after fourth week of incubation in different growth regulator combinations tested. Highest amount of calli were in MS medium in the presence of 2.25 mgl-1 BAP and 1.0 mgl-1 2,4-D. Fragile calli, which were transulant and mucilaginous in nature were observed within 15 days of incubation, which could lead to cell suspension cultures.

In vitro callus induction of Spilanthes calva DC [Spilanthes acmella auct. nonL,.] (Maha Akmella)

Spilanthes calva DC. (Maha Akmella) is a valuable medicinal plant belongs to Family Asteraceae. It is widely used in indigenous medicine to treat toothache in most of the Asian countries. Not only it has anesthetic properties, but also contain secondary metabolites, with the insecticidal properties, which could be used as potential bio insecticide. This is an annual plant, which grows to a height about 30 cm. After flowering mother plant is dried off. Four to six weeks later seeds are germinated and new seedlings are produced. Viability of seeds loses within short period of time. Even though seeds are germinated percentage of germination is low (about 30%). Rooting of cuttings is also not possible. This is a limitation in using this valuable medicinal plant for commercial production. Therefore it is very important to develop a protocol for mass propagation through tissue culture and establishing cell cultures will be useful for large-scale chemical extraction in industrial purposes.

Leaf discs were used as explant for callus initiation. In order to identify the suitable maturity stage for callus initiation, leaves were harvested at different maturity stages i.e first, second and third fully opened leaf.

Leaves were washed with Dettolä soap and soaked in a solution of Teepolä for 5 minutes. After that leaves were washed with running tap water for 45 minutes. In order to surface sterilize. Leaves were washed with 10% Cloroxä (5.25% Sodium hypochlorite v/v) for 5 minutes and then with 70% alcohol for 30 seconds each followed by three successive washings in sterile distilled water. These operations were carried out inside the laminar airflow cabinet before inoculation. Basal media tested for the study were full strength MS (Murashige and Skoog, 1962) medium and ½ MS (both macro and micronutrients) medium. Media were supplemented with different concentrations (1.0 mgl-1 – 3.0 mgl-1) of BAP and 2,4-D. Cultures were incubated under complete dark at 25±1°C in the growth room.

Study conducted by Haw and Keng (2003) on the same species produced multiple shoots from axillary bud explants without inducing callus in MS medium supplemented with 2.0 mgL-1 BAP. In the present study, callusing was observed within 5 days of incubation in full strength MS medium supplemented with BAP and 2,4D. It took longer period to initiate callus when both macro and micro nutrients in the basal medium was lowered to half and the amount of callus produced was also very low even after 6th week of incubation. In order to observe the time taken to produce maximum amount callus fresh weight was measured after 2nd, 4th and 6th week of incubation. It was observed that maximum amount of callus was produced within 4 weeks in all explant types tested with a maximum of 0.88 g ± 0.23 in leaf discs obtained from first fully opened leaf.

In order to determine the best growth regulator combination for callus initiation, calli fresh weights were measured after fourth week of incubation in different growth regulator combinations tested. Highest amount of calli were in MS medium in the presence of 2.25 mgl-1 BAP and 1.0 mgl-1 2,4-D. Fragile calli, which were transulant and mucilaginous in nature were observed within 15 days of incubation, which could lead to cell suspension cultures.

 S Hewage and W T P S K Senarath
Department of Botany, University of Sri Jayewardenepura, Sri Lanka.

Effect of bio control agent Trichoderma (T. viride and T. konnigii) on basal rot of Cloropytum comosum ‘laxum’ caused by Sclerotium rolfsii

At present, the biological control of soil borne fungal diseases is becoming popular in foliage industry of Sri Lanka, which is a nature-friendly ecological approach to overcome the problems caused by standard chemical methods of plant protection. With a suitable bio control agent pathogen can be suppressed and reduced the disease incidence could be reduced effectively. This experiment was conducted over a period of six months in polytunnel to identify a potential bio control agent for basal rot of Cloropytum comosum ‘laxum’ caused by Sclerotium rolfsii with five treatments of Trichoderma viride, Trichoderma konnigii and combination of Trichoderma viride and Trichoderma konnigii, Pormarsol forte 80% wp and control. The mean disease incidences of above treatments were 1.75, 2.75, 1.5, 1.75 and 10.75 respectively. It was revealed that Trichoderma viride and combination of Tricoderma spp. are suitable for the highly effective control of plant diseases caused by Sclerotium rolfsii.

K A L Priyadarshani and D B Kelaniyangoda
Department of Horticulture and Landscape Gardening, Wayamba University of Sri Lanka, Sri Lanka