Screening rice varieties for resistance to fissuring for improved milling quality
1987
Ibabao, M.G.B. | Perez, C.M. | Juliano, B.O. (International Rice Research Inst., Los Banos, Laguna (Philippines). Cereal Chemistry Dept.)
Grain fissuring occurs during moisture adsorption of relatively dry grain and contributes to poor head rice yield. A model screening method for moisture adsorption tolerance (fissuring resistance) was developed based on an actual micromilling test. An infrared moisture balance was used to reduce the weight by 2% for 8.0g rough rice in 90s. The dried grains were then stressed overnight (65-80%RH, 28-31 deg C), dehulled, and 5.0 g brown rice was milled in a Kett Pearlest mill for 1 min. IR64 and IR28150-84-3 (intermediate amylose content and intermediate gelatinization temperature) had better head rice yield (HRY) from stressed rough rice than IR42 (high amylose and low gelatinization temperature). Batch drying of samples using a forced-draft oven at 44-47 deg C improved the screening method because more samples could be subjected to identical stress with less operator time. Studies of field grain samples of 29 IR varieties and IR28150-84-3 harvested in the 1985 wet season at normal maturity and one week later showed that the one week delay in harvest was not effective in inducing fissuring in susceptible varieties. A fixed artificial stress such as drying to remove a constant moisture content and then exposure to a humid condition was a more sensitive method. IR42 showed lower HRY than IR64 in 45s but not in 90s at 2 percentage points moisture loss. However, drying conditions had to be optimized for each crop using IR64 and IR42 as check samples.
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