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Preferred Rice Varieties, Seed Source, Disease Incidence and Loss Assessment in Bakanae Disease

K. S. Hossain
Department of Botany, Jagannath University, Dhaka, Bangladesh

M.A.T. Miah
Plant Pathology Division, BRRI, Gazipur, Bangladesh

M. A. Bashar
Department of Botany, Dhaka University, Dhaka, Bangladesh,

Abstract/ Executive Summary:

Rice (Oryza sativa L.) is the principal food crops in Bangladesh. Here different rice varieties are grown in 3 rice growing seasons per year viz. Aus, Aman and Boro. Eleven rice varieties were grown at randomly sampled 50 farmers’ plots in Chandiara village during Boro (November, 2007 – May, 2008), Aus (April – July, 2008) and T. Aman (July – December, 2008) seasons. Among the varieties farmers were preferred BRRI dhan 28 mostly during the Boro and Aus seasons. During the T. Aman season it was BRRI dhan 32. All the farmers’ plots were seeded with BRRI released varieties during the T. Aman season though it was 90 and 82% during the Aus and Boro seasons respectively. In these 3 seasons most of the farmers did not procure certified seeds of BADC or non-government agencies. 62 to 88% rice plots per season were seeded with farmer saved seeds in the sampled plots. Bakanae disease incidence was much higher in these plots and comparatively less frequent in the plots seeded with certified seeds of different agencies. All rice varieties grown in the sampled area during this study were found more or less susceptible to the disease. The highest disease incidence (19.1%) was found in the T. Aman followed by the Aus and least frequent in the Boro season. 10.85% grain yield loss due to the disease was estimated by following a modified method and simplified formula during the T. Aman season. Yield loss was observed mainly due to reduction of effective tillers.

Keywords: Bakanae, Incidence, Rice varieties, Seed source, Yield loss

Location: Chandiara village near Chandina upazilla in Comilla district

Start Date: 00-01-2008

End Date: 00-12-2008

Program Area: Pest Management

Commodity: Diseases

Objectives:

1. This study presents relation among rice varieties, growing seasons & their seed source and a modified method & simplified formula for estimating bakanae disease incidence and yield loss in rice.

Methodology:

Several bakanae infected farmers’ rice plots were observed in the three successive rice growing seasons viz. Boro (November, 2007 – May, 2008), Aus (April – July, 2008) and T. Aman (July – December, 2008) at Chandiara village near Chandina upazilla in Comilla district. In each season, one farmer’s plot was selected randomly and then 49 plots were selected around the first plot. All these farmers’ plots were contiguous, quadrilateral and varying areas. Number of hills at each sidelines of every plot was counted. From this count, total number of hills for each plot was calculated by multiplying the average number of hills between two opposite sidelines with the average number of hills between the opposing two sidelines. For each plot number of hills with bakanae symptom, varietals’ names and seed sources were recorded at maximum tillering stage for each rice growing season during the study period. Disease incidence in term of percentage of infected hills for each plot was calculated by the following formula, Disease Incidence (DI) = (Infected hill per plot/Total hilld per plot)x100. In total, three hundred bakanae-infected hills were randomly selected from these fifty rice plots during T. Aman season of 2008. Each hill was labelled with number tags. For each infected hill, an adjacent healthy hill was also labelled with an appropriate tag, to obtain a comparable pair of infected and healthy hills. Among the 300 pairs of infected and healthy hills, finally 150 pairs of hills were selected with care so that interference of other disease and pests could be minimized. These 150 pairs of labelled hills were then harvested and brought to the Bangladesh Rice Research Institute (BRRI) laboratory for necessary data collection. Effective tiller number, grain weight and per cent grain moisture for individual hills were recorded. All grain weights were calculated at 14% grain moisture. Per cent grain yield loss per infected hill (% YLIH) was estimated following the formula: % YLIH = (GWHH - GWIH)/ GWHH x 100, Where, GWHH= Grain weight per healthy hills, and GWIH= Grain weight per infected hills. Average value of grain yield loss in 150 infected hills was used for grain yield loss calculation. Grain yield loss in the sampled plots was estimated using the following formula. Grain yield loss = %DI x %YLIH x 100% This formula is the simplification of the formula reported by Rathaiah et al. (1991). The simplification was made as: 100% – % infected hills x 33 + % healthy hills x 100/100. Where, 33, representing ‘grain yield per infected hill (% GYIH)’ which was calculated by subtracting YLIH (67%) from 100%; %healthy hills was calculated by subtracting %infected hills from 100% and 100/100 representing 100%. Therefore, Grain yield loss=100% – % infected hills x 33 + % healthy hills x 100/100 =[100% –{%infected hills x (100% –% YLIH) +(100% –% infected hills)}]x 100% = [100% –{%infected hills x 100% –%infected hills x %YLIH +100%–%infected- hills}]x100% = [ 1 – %infected hills + %infected hills x %YLIH– 1 + %infected hills] x 100% (As, 100%=1) = %infected hills x %YLIH x 100% = %DI x %YLIH x 100%.

Source of Information: J. Agrofor. Environ. 5 (2): 125-128, 2011; ISSN 1995-6983

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

All rice varieties grown in the sampled area during this study were found more or less susceptible to the disease. The highest disease incidence (19.1%) was found in the T. Aman followed by the Aus and least frequent in the Boro season. 10.85% grain yield loss due to the disease was estimated by following a modified method and simplified formula during the T. Aman season. Yield loss was observed mainly due to reduction of effective tillers.

Knowledge Management: Journal