Experimental Site and Seed Sowing
An experiment was conducted at the Field Laboratory of Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh during the period from July 2012 to December 2012. A high yielding cultivar BR11 (Mukta) was selected for this study. Seeds of BR11 (Mukta) were collected from seed store of Bangladesh Agricultural Development Corporation (BADC), seed building, Monakhola, Mymensingh.
A small piece of medium low land of the experimental farm of the Department of Plant pathology, Bangladesh Agricultural University, Mymensingh was puddled with the power tiller. Clean and mature seeds were soaked in tap water for 24 hours and incubated 48 hours for germination before sowing in the seed bed. The germinated seeds were sown in the seed bed on 5 July 2012.
Field Experiment Setting
The experiment was laid out in a Randomized Complete Block Design (RCBD) with 3 replications maintaining distance between the blocks and the plots as 50 cm and 25 cm, respectively. A total of 7 treatments were used henceforth designated as T0 (Control), T1 (Compost tea as foliar spray 2 times (preventive) @ 1:5 w/v, T2 (Compost tea as foliar spray 2 times (Curative) @ 1:5 w/v, T3 (Streptomycin as foliar spray 2 times (preventive) @ 1gm/10 L, T4 (Streptomycin as foliar spray 2 times (Curative) @ 1gm/10 L, T5 (Cupravit as foliar spray 2 times (preventive) @ 0.2%) and T6 (Cupravit as foliar spray 2 times (Curative) @ 0.2%. The main land was prepared by power tiller on 8th August 2012. Later on the individual plots were cleaned from weeds and stubbles. Organic amendments and Chemical fertilizers were applied in the field as recommended by Bangladesh Agricultural Research Council (Anonymous, 2005). The border of each unit plot was raised to prevent the fertilizer and nutrients movement from one plot to others.
Transplanting of Seedlings of BR 11 (Mukta) and Preparation of Compost Tea
After preparing the land, 32 days of old seedlings of BR 11 (Mukta) were uprooted carefully to avoid root injury. The seedlings were transplanted putting three seedlings/hill where plant to plant and row to row spacing were 15 cm and 20 cm, respectively. Weeding and other cultural practice was performed in time. Compost tea was obtained by mixing compost with tap water at a ratio of 1:5(w/v) followed by fermentation for one week. Then it was stirred once every day and allowed to ferment in the Net house of Seed Pathology Centre, BAU, Mymensingh at 25°C. After 7 days, the solution was filtered through cheese cloth to obtain the compost tea.
Inoculum preparation and Inoculation of test entries
BXO9, a virulent and reference isolate of major races of Xanthomonas oryzae pv. oryzae (Khan et al., 2010) was obtained from the Plant pathology Division, BRRI for inoculation. The isolate was cultured on Peptone Sucrose Agar (PSA) slants for 72 hours at 30ºC. Inoculum was prepared by mixing the cultured bacteria with 10 ml sterile distilled water in a slant. Before inoculation the concentration of the bacterial suspension was adjusted to 108 to 1010 CFU/ml. using sterile water. The leaf clipping inoculation method was adopted in this experiment. The scissors were dipped into bacterial suspension, and then the tip of fully expanded leaves were clipped as described by Kauffman et al. (1973).
Identification of the symptom of Bacterial Leaf Blight of rice
The rice plants were examined periodically and bacterial leaf blight infection was identified on the basis of symptoms developed on the plants as described by Tabei and Mukoo (1960). At first a tiny water soaked lesion appeared from the leaf margin, then turned yellow while enlarging both the length and width to develop an elongated irregular lesion. The border of the lesion adjoining the healthy part showed a wavy margin lesions might start on one or both margins of the leaf.
Assessment of incidence and severity of disease
Data on lesion length, relative lesion length and leaf area damaged were recorded at 7 and 14 days after inoculation (DAI). Lesion length was measured by measuring scale. Total number of inoculated leaves per hill and number of infected leaves per hill was recorded. Both at natural and inoculated conditions, 5 hills and 5 leaves were randomly selected from each plot to collect data on total number of leaves per hill, number of infected leaves per hill, total leaf length (cm) and leaf lesion length (cm).
The disease incidence was calculated by the following formula:
Disease incidence (I)% = (Number of infected leaves)/ (Total number of leaves) X 100
Percent leaf area diseased/severity was assessed by the following formula:
Severity %= (Leaf area diseased) / (Total leaf area) X 100
Harvesting and recording of data
Randomly selected 15 tillers from each plot (inoculated and non-inoculated) were used for recording the data on Plant height (cm), No of tiller/plant, Panicle length (cm), Total number of grains/panicle, Chaffy grain number/ panicle and Grain weight (gm)/plot.
Analysis of data
The collected data were analyzed using the Analysis of variance (ANOVA) technique, and the mean differences were adjudged by Duncan’s Multiple Range Test (Gomez and Gomez, 1984) using the statistical computer package.