MAI Khan
SSO
Plant Pathology Division
BRRI Gazipur
M R Bhuiyan
SSO
Plant Pathology Division
BRRI Gazipur
MS Hossain
PSO
Training Division
BRRI Gazipur
Aeromatic rice, Grain yield, Seed quality, Neck blast disease
Pest Management
Plant Materials, Cultural Conditions and Disease Assessment: Three aromatic rice cultivars namely BRRI dhan34, Sakkorkhora and Kalijira were selected in the present study. Total number of panicles including diseased and healthy of a one square meter of land were collected from three points diagonally of the same field during Wet Season (July – December), 2013. The collected panicles were initially graded in to two groups, diseased and apparently healthy. The diseased groups were then classified in to their severity scale. Based on the number of panicles with each disease scale, computed panicle blast severity (PBS) as follows:
(10 N ) (20 N ) (40 N ) (70 N ) (100 N ) Panicle blast severity (PBS)/Total number of panicles observed
Where N1 – N9 are the number of panicles with score 1-9: 1= Lesions on several pedicels or secondary branches; 3= Lesions on a few primary branches or the middle part of panicle axis; 5= Lesion partially around the base (node) or the uppermost internodes or the lower part of panicle axis near the base; 7= Lesion completely around panicle base or uppermost internodes or panicle axis near the base with more than 30% of filled grains; 9= Lesion completely around panicle base or uppermost internodes or the panicle axis near the base with less than 30% of filled grains.
Yield traits and grain size measurements: One hundred panicles from each group (either healthy or diseased) were separated randomly for yield traits and grain size measurements. Panicle length, filled and unfilled grains/panicle and grain sterility percentages of diseased and healthy panicles were determined. Panicle weight, grain length, width and their ratio, and 1000 grain weight with corresponding moisture of diseased and healthy panicles were determined after 3 days of sun drying. The length and width of the grains were measured using digital 102 slide calipers. The grain yield of healthy or diseased conditions were estimated by examining yield performance is to break the yield into its components. Where, Grain yield (t/ha) = panicle number/m2 104 × grain number/panicle × % filled grains × 1000 grain weight (g) × l0-5105 . In case of healthy condition, we used average grain number/panicle, % filled grains and 1000 grain weight of healthy panicles. In the same way, we used yield component data of diseased panicles for yield estimation of diseased condition. All the grain weights were adjusted to 14% moisture content calculated by dry weight basis.
Determination of grain quality and blast pathogen transmission to seeds: Grain quality of the freshly harvested air dried seeds of respective variety was determined by yielding seed borne pathogen presence in filled and unfilled grains. Occurrence of seed borne fungi on seeds was determined by the modified blotter method without seed surface sterilization. Twenty five seeds (either filled or unfilled grain) of each cultivar selected at random were spaced on damp 9 cm Whatman No. 1 filter paper in plastic petri dishes and each was replicated sixteen times. The plates were incubated in 12-hr light and 12-hr darkness at 25±2 ºC for 4 days to detect blast pathogen and continued it up to 8 days for other fungi detection. After the incubation period, conidia and hyphae of fungi growing on the seeds were picked off each 120 infected seed with fine needles, mounted on a slide, and examined with a compound microscope. Each fungus was identified on the basis of its conidia and/or hyphae2 characteristics and frequency of isolation was tabulated. Transmission of blast pathogen from panicle base 123 or branches to seeds was determined by the isolation frequencies of blast pathogen from freshly harvested seeds of neck blast infected panicles. In this case, seed samples were investigated without surface sterilization. Because, as an airborne pathogen, still it is not clear whether blast pathogen exist on seed surface or as systemic pathogen.
Data analysis: The data of apparently healthy and diseased panicles were compared through student t. test. Field data on neck blast incidence and severity were analyzed using Crop Stat for Windows Version 7.0.2007.0 at 5% level of significance.
Science Directory:337(2014):635-641
Journal