Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/1/2006
Publication Date: 2/15/2006
Citation: Kepiro, J.L., Fjellstrom, R.G., McClung, A.M. 2006. Evaluating milling yield in a Cypress x Panda cross with traditional, re-milling and re-wetting techniques. Rice Technical Working Group Meeting Proceedings, February 29-March 1, 2006, Houston, Texas. 2006 CDROM.
Technical Abstract: Milling yield, defined as the percentage of whole rice kernels recovered after de-hulling rough rice and milling, is a critically important trait in rice. Milling yields vary considerably between cultivars with low milling cultivars rejected by rice growers. It is a complex trait comprised of component traits, each of which is under the control of numerous loci. Breeding for improved milling yield is difficult because of the numerous sub-component traits, the quantitative inheritance, and the impact of the pre- and post-harvest environment on the grain. In conjunction with an investigation of quantitative trait loci associated with milling yields determined using standard milling procedures, a "Re-milling" protocol to measure kernel strength and a "Re-wetting" technique to simulate the affect of high moisture pre- and post-harvest environments on milling yield were tested. The cultivar Cypress, well-known for high and stable milling yield over a wide range of harvest moisture levels, was crossed with the cultivar Panda, characterized by low milling yield to produce 137 F11 progeny lines for milling yield evaluation. Two row plots of the 137 families were harvested at estimated field moisture of 18-21%, threshed, and the moisture content determined using a Dickey-John grain moisture meter. The rough rice was placed in paper bags and stored in a climate controlled environment for approximately two months to allow moisture equilibration to ~12%. Four samples of rough rice from each family were then prepared for milling, two aspirated 125g samples for standard milling, and two un-aspirated 125g samples for re-wetting followed by milling. Standard milling began with the 125g samples of aspirated rough rice de-hulled with a Sataki (rubber roll) de-huller. Brown rice was milled for 54 seconds in a McGill No. 2 mill with a 636g weight located at the middle position (12 cm) of the mill's saddle arm. The milled rice was separated with a shaker/separator and kernels with length greater than or equal to a ¾ full length kernel were considered whole kernels. Grain recovered after milling and separating was weighed, and standard milling yields were calculated based on the proportion of whole milled grains to the total milled rice. A 100g sample of the whole kernel milled rice recovered from the standard milling procedure was re-milled to determine kernel strength of whole milled kernels. Additional force was applied to the grain during re-milling with a 1471g weight located at the middle position (12 cm) of the mill's saddle arm. The re-milled milling yields were calculated based on the proportion of whole re-milled grains to the total re-milled rice. Rough rice samples were re-wetted by soaking in water to simulate a rain event in the field or a fluctuation from low to high humidity during storage. The samples were placed in perforated boil bags and sealed with a Food-Saver™ plastic bag sealer. The samples were soaked in 26.70C (800F) tap water for two hours, dried with un-heated forced air for 12 hours to ~12% moisture; and place in a climate controlled environment to equilibrate for 72 hours. The samples were then milled using standard milling techniques. The milling yields of the re-wetted samples were calculated based on the proportion of whole milled grains to the total milled rice. Re-milled and Re-wetted milling yields are being compared with standard milling yields. Re-milled whole kernel milling yields will be analyzed to identify markers specifically linked to kernel strength, and re-wetted milling yields will be analyzed to find markers associated with moisture induced fissuring. Progress will be presented in the poster.