Submitted to: Planta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/22/2011
Publication Date: 12/20/2011
Citation: Miller, H.B., Miller, G.H., Moldenhauer, K.A. 2011. Utilizing the genetic diversity within rice cultivars. Planta. 235:641-647. Interpretive Summary: Modern rice breeding emphasizes improvement in yield, disease resistance, and grain milling quality. However, other traits such as bran carotenoids (vitamin-containing pigments that impart a yellow color to grains) that historically have not been of interest could add value to rice in some niche markets, or could serve as tools to better understand the genetic control of these traits. Some residual genetic variability is present in many rice cultivars that are otherwise true-breeding. Thus, it is possible to select for improved genetic traits within an established variety. From single varieties containing high levels of variability for particular traits, we developed separate lines that exhibited diverse levels of these traits. Evaluating the variety RU9101001 and the warm- and cold-temperature-sprouting lines derived from it as examples, we used molecular markers (SSRs) to demonstrate that residual heterogeneity was present within the original variety and that the original heterozygosity was separated in the two derived lines. Detailed screening of other varieties also allowed us to develop lines exhibiting low and high levels of several other traits including cold-temperature-sprouting from RU9101001 and Bonnet 73; postharvest grain yellowing from Tominishiki; early tiller (stem) production from Hei Jaio and Tominishiki; and bran carotenoid levels from Spring. Exploitation of this phenomenon would be useful for crop improvement in the future because it might be an efficient approach to develop new lines with niche characteristics using existing commercial rice varieties, or to develop specialty lines for genetic and biochemical investigations.
Technical Abstract: Plant breeding of rice emphasizes improvement in yield, disease resistance, and milling quality. Numerous other traits (e.g., bran carotenoids) that historically have not been selected for could provide added value in expanding niche markets, as well as be useful tools for understanding the genetic control of these traits. Residual heterogeneity is present in many rice cultivars; therefore, it is possible to select for different alleles within an existing cultivar. This genetic variability may be due to heterogeneity, a mixture of individuals with different homozygous alleles or due to heterozygosity, presence of different alleles in the same individual. By identifying and using cultivars with high levels of variability for a trait, we were able to develop separate lines from single cultivars that showed high and low levels of that trait. The rice cultivar RU9101001 and the warm- and cold-sprouting lines that were derived from it were used to demonstrate that residual heterogeneity was present within a cultivar and that the original heterogeneity was separated in the derived lines. Rice simple sequence repeat markers were heterozygous in the parent RU9101001 cultivar, but the cold-sprouting lines were homozygous for one set of alleles and the warm-sprouting lines were homozygous for the other set. Through detailed phenotypic screening, we developed lines that exhibited low and high levels of the following traits in the specified cultivars: cold-sprouting from RU9101001 and Bonnet 73, postharvest yellowing from Tominishiki, early tillering from Hei Jaio and Tominishiki, and bran carotenoid levels from Spring. If variability exists in a cultivar, then utilization of residual heterogeneity may provide a quicker and more efficient means to develop lines with special characteristics using cultivars that are already agronomically valuable or to develop near isogenic lines for genetic and biochemical investigations.