Mapping and validation of quantitative trait loci associated with tiller production in rice (Oryza sativa L.)

Authors: Pinson, Shannon; WANG, YUEGUANG - Texas A&M Agrilife; TABIEN, RODANTE - Texas A&M Agrilife

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2015
Publication Date: 7/1/2015
Citation: Pinson, S.R., Wang, Y., Tabien, R.E. 2015. Mapping and validation of quantitative trait loci associated with tiller production in rice (Oryza sativa L.). Crop Science. 55:1-15. doi: 10.2135/cropsci2014.09.0644.

Interpretive Summary: Rice tillers are culms or stems that arise from the nodes of another stem. The number of tillers per plant is an important yield component in rice. As a general rule, temperate and tropical japonica cultivars produce few tillers, compared with indica rice genotypes. An increase in tiller production, especially early in the vegetative stage, is desired in order to increase yield potential and enhance ability to shade and suppress weeds. Rice breeders would like to increase rice grain yields by optimizing the network of genes that regulate the production of grain-bearing tillers. The objective of this study was to identify quantitative trait loci (QTLs) associated with enhanced early tillering to improve breeders’ ability to select for tiller production in improved rice cultivars.

Technical Abstract: Rice has two main subspecies under world-wide production; the indica rices, grown primarily in tropical rice-growing regions, tiller profusely compared to the japonica rices which are grown in temperate and subtropical regions, including the U.S. All breeders seek to increase yield potential by optimizing the genetic network that determines the number and timing of tiller production. However, japonica rice breeders seek to increase tiller number per plant (TN) to increase yield, whereas indica breeders seek to limit the extensive development of unproductive tillers. The present study took advantage of the japonica vs. indica differences by identifying chromosomal regions associated with tiller number (TN) within a japonica x indica rice mapping population. In rice, it is not just the number of tillers produced, but also the tillering pattern and timing that determines whether or not a tiller will survive and produce a grain-bearing panicle prior to harvest. We observed TN over time (sequential observations from weeks 5 through 10), and recorded which nodes on the main stem gave rise to tillers, and the total number of leaves (nodes) produced by the plants (which reflects how fast the plants are growing overall). This study identified 9 chromosomal regions for TN, and demonstrated that identification of high-TN progeny could be accomplished by counting tillers once on 8- to 9 -week-old seedlings. High TN was associated with early tiller production, which was in turn associated with rapid production of culm nodes (leaves). While the present TN results extend to other grass species, the most immediate benefits will be to rice breeders. Because these tillering genes were identified in a mapping population previously used to identify more than 250 chromosomal regions associated with several plant traits, we can determine, for example, that the TN gene on chromosome 8 shows desirable linkage with other yield-component traits and disease resistance. Knowledge drawn from the larger body of data can be used by breeders to prioritize between the TN genes, and design breeding strategies that can most effectively move desired genes/traits into rice cultivars enhanced for specific production systems. Selection for tillering under field conditions is difficult because tillering is known to be sensitive to a wide range of environmental cues, including depth of seeding and water level, which are especially difficult to control precisely under field conditions. The markers reported here as linked to the TN genes can support marker-assisted breeding.