RESPONSE OF DIVERSE RICE GERMPLASM TO BIOTIC AND ABIOTIC STRESSES
Title: New method opens opportunity to proactively select for fissure resistance in early breeding generations
Submitted to: Texas Experiment Station Field Day Handout
Publication Type: Experiment Station
Publication Acceptance Date: June 2, 2010
Publication Date: June 29, 2010
Citation: Pinson, S.R., Gibbons, J.R., Jia, Y. 2010. New method opens opportunity to proactively select for fissure resistance in early breeding generations. Texas Experiment Station Field Day Handout. VI-VII - http://beaumont.tamu.edu/eLibrary/Newsletter/2010_Highlights_in_Research.pdf..
WANTED: New rice varieties improved for resistance to kernel fissuring. Rice kernel fissuring is one of the leading causes of reduced milling yield. Any reduction in fissuring can result in direct increases in yield and profit for both producers and millers. While most U.S. rice varieties yield around 55% head rice, ‘Cypress’, ‘Saber’ and ‘Cybonnet’ typically yield 60 to 65% head rice, 5 to 10 percentage points better than standard varieties. For a producer yielding 7000 lb/acre paddy, even a relatively small (5%) improvement in milling yield can increase profits by $18/acre based on Spring 2010 prices for whole and broken long grain rice.
PROBLEM: Breeders cannot select for a trait unless they can see or detect it. The most reliable method breeders have had for evaluating fissure resistance involves harvesting sequentially drier rice samples from a single, large research plot then milling the dried samples to evaluate milling quality over time. Rapid loss of milling quality over sequentially drier harvests indicates high susceptibility to kernel fissuring; slow loss of milling quality indicates fissure resistance. While this sequential-harvest method has proven capable of detecting even small (2%) differences in fissure resistance, it requires large amounts of seed, field space, and labor. As such, it cannot be conducted until late in the breeding process, after much breeding effort has been expended to reduce the number of lines under consideration for variety release to < 100 lines. While this allows breeders to reactively select against fissure-susceptibility before actual variety release, proactive selection for a desired trait resulting in rapid breeding gains requires selection in early breeding generations, such as the F2 or 1st generation.
SOLUTION: A laboratory method wherein small samples of seed (50 to 100 kernels) are evaluated for in-lab fissure rates after controlled exposure to humid conditions was previously shown by scientists in TX, LA, and CA to reliably identify fissure resistance among late-generation pure-breeding material. We extended the utility of this lab method by documenting that it was successful at identifying fissure resistant progeny among 300 Cypress x LaGrue F2 plants.
Research details: Unfissured, mature seed was harvested from 300 Cypress x Lagrue F2 plants in 2006 and evaluated for in-lab fissure response, The 30 most resistant (FisR), and the 30 most susceptible (FisS) F2 plants were selected, and their F3 progeny seed were then grown and evaluated for fissure resistance in 2007. The FisS F2:3 progeny fissured twice as much as the FisR progeny, providing a first indication that the in-lab selection method was successful at identifying FisR F2 progeny. A second round of selection was conducted, identifying the most FisR and FisS F3 plants, and their progeny were again evaluated for fissure response in 2008 and again in 2009. The FisR selections proved to be equal to, but not more resistant than Cypress, and the most FisS selections appeared equal to LaGrue in lack of fissure resistance. This study documented, for the first time ever, successful early-generation selection for FisR, opening new opportunity for breeders to develop rice cultivars improved for this important agronomic trait.