Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/25/2011
Publication Date: 2/1/2013
Citation: Pinson, S.R., Jia, Y., Gibbons, J. 2013. Response to early generation selection for resistance to rice kernel fissuring. Crop Science. 52:1482-1492. Interpretive Summary: The value of milled rice depends on the percent whole versus broken kernels after milling. Broken rice commands about half the market value as whole milled rice, so one goal of rice breeders is to increase the ability of the rice kernel to remain unbroken during the milling process. One of the primary causes of rice breakage is fissuring, or cracking, of the rice before it is milled. A common cause of rice fissuring is the exposure of drying, mature kernels to humid field or postharvest conditions that cause the kernels to reabsorb moisture. Some rice varieties produce grain more resistant to fissuring than others, and breeders would like to incorporate genes controlling fissure resistance into new rice varieties. This study showed that a laboratory method for evaluating fissuring resulted in successful selection for fissure resistance (FR) in the first (F2) and second (F3) breeding generations. The selections were conducted in both fissure resistant (FR) and susceptible (FS) directions to better measure the power of the selection technique. The success of the selections was demonstrated by the fact that the second generation was more FR (or conversely more FS) than the first breeding generation. This opens new opportunity for rice breeders to more efficiently develop new US rice varieties with improved fissure resistance, resulting in less rice breakage and greater crop value. Association between FR and short plant height in the present study suggests that one of multiple FR genes is linked to the semidwarf locus on chromosome 1. The effective phenotyping provided by this method can also support studies aimed at identifying molecular gene tags associated with FR genes.
Technical Abstract: The value of milled rice (Oryza sativa L.) depends on the percent whole versus broken kernels after milling. Kernel fissures caused by pre- or post-harvest stresses are the leading cause of breakage upon milling. ‘Cypress’ is known to be more fissure resistant (FR) than most cultivars, but breeding success has been limited by a lack of ability to identify FR among F2 and F3 progeny. An induced-fissuring method wherein small samples of seed are evaluated for fissure rates after controlled exposure to humid laboratory conditions can distinguish FR among pure-breeding rice cultivars. To measure the efficacy of the induced-fissuring system for evaluating FR among segregating breeding progeny, we applied divergent selection for FR and susceptibility (FS) on seed harvested from ~300 Cypress (FR) x ‘LaGrue’ (FS) F2 plants, and evaluated selection success using seed from F2:3 plants grown in AR and TX. F3 selections and F3:4 progeny testing followed. FS F2:3 progeny fissured twice as much as FR progeny, with an average response to selection of 13.5%. Response to F3 selection was smaller, averaging 2.6%. Broad-sense heritability averaged 0.38 +/- 0.13. Narrow-sense heritabilities were 0.47 and 0.54 for the FR and FS F2 selections, respectively, and smaller thereafter due to the reduced response to F3 selection. This study documented successful early-generation selection for FR, opening new opportunity for breeders to develop rice cultivars improved for this important trait.