APPLICATION OF RICE GENOMICS TO DEVELOP SUSTAINABLE CROPPING SYSTEMS FOR THE GULF COAST
Title: AFLP markers linked with long grain milling yield
Submitted to: Scientific and Technical Review
Publication Type: Other
Publication Acceptance Date: March 31, 2007
Publication Date: April 1, 2007
Citation: Kepiro, J.L., Fjellstrom, R.G., Mcclung, A.M. 2007. Aflp markers linked with long grain milling yield. RiceCAP News: http://www.uark.edu/ua/ricecap/Communication/newsletters/RiceCAPv3n7_Apr07.pdf. pp. 4-6.
Milling yield is an important trait in rice because it is a major factor determining the price farmers are paid for their crop. To address this issue, the United States Department of Agriculture, Agricultural Research Service, Rice Research Unit in Beaumont, TX launched an investigation to identifying AFLP molecular markers linked to milling components and their sub-component traits in an effort to give breeders new tools to efficiently select for superior milling rice varieties. The project has been underway since October 2003 under the direction of Dr. Bob Fjellstrom and his post-doctoral research associate, Dr. Joe Kepiro.
Breeding for improved milling yield is difficult because the trait is complexly inherited. To determine milling yield, rough (paddy) rice is hulled to produce brown rice (BR). The brown rice is then milled to produce total milled rice (MR), followed by separation into whole and broken kernels. The proportion of whole milled kernels derived from paddy rice is considered head rice (HR), or whole grain milling yield. Each of these milling components is affected by multiple traits (milling sub-components). Many of the sub-component traits are under the control of numerous genes, and therefore the genetic inheritance is complex. Furthermore, these sub-component traits may be affected by environmental (non-genetic) factors, including weather conditions prior to harvest and post-harvest handling of the grain. This makes evaluation and selection of superior milling varieties very difficult and labor intensive.
This project used 137 advanced progeny lines derived from a Cypress x Panda cross grown in Beaumont during 2002 and 2004 to map chromosomal regions associated with milling yield. Both parents are early maturing long grain varieties. Cypress has intermediate amylose content and is well-known for high and stable milling yield (~ 64%) over a wide range of harvest moisture levels, whereas Panda has low amylose content, and is characterized by low milling yield (~ 52%).
Conventional milling techniques were used to obtain BR, MR, and HR. In addition, the total milled rice recovered from BR (MR/BR), and the proportion of whole milled rice recovered from total milled rice (HR/MR) was calculated. A WinSeedle™ (2005a Pro) color image analysis system (Figure 1) was used to measure kernel length and width for both brown and milled rice; whereas kernel thickness was measured by hand. The number of broken and full length brown rice kernels was used to calculate the proportion of brokens in the brown rice after hulling, but prior to milling (pre-broken). The WinSeedle system also allowed development of an accurate method for quantifying the area of chalkiness (Chalk) and greenness on a per kernel basis. Amylose content (AMY), which influences cooking quality, was measured using standard analytical procedures.
The trait having the greatest effect on whole milled rice recovery was pre-brokens and the traits with the largest effect on pre-brokens were chalk and apparent amylose (Table 1). BR was directly correlated to MR, but was unrelated to HR, whereas MR was moderately correlated to HR. However, chalk and apparent amylose were negatively correlated to both HR and whole milled rice recovery, suggesting that grain chemistry may impact milling.