QTLs for Early Tiller Production and Relationships with Rapid Seedling Growth and Increased Panicle Number in Rice

Abstract

Tiller number (TN) is a key determinant of final grain yield in the small grains crops, including rice (Oryza sativa L.), and is desired to enhance competition with weeds. Quantitative trait loci (QTLs) associated with TN were mapped within a set of recombinant inbred lines developed from a cross between the low‐tillering tropical japonica cultivar ‘Kaybonnet‐lpa1‐1’ and the high‐tillering, high‐yielding, early‐maturing indica cultivar ‘Zhe733’ using data collected from greenhouse potted plants evaluated weekly. Relationships between the five identified TN QTLs and related traits including panicle number (PN), flag leaf number, seedling leaf number (SLN), and earliness of tiller production were also evaluated. The three TN QTLs that were linked with early tiller emergence were also associated with PN; two additional TN not associated with PN were also identified. All five TN QTLs were also SLN QTLs, though other loci affecting SLN were also identified. Several of the TN and SLN QTLs identified using data from young plants (e.g., ≤6 wk after planting) were not detectible in data collected just before or after heading. The three TN QTLs also associated with PN showed stronger effects (higher logarithm of the odds ratios and additive effects) on TN as observed in seedling stages than on final TN at heading time, and their effects diminished over time to the point that they were not always detectible in TN data collected at or after heading. However, the three TN QTLs that were also PN QTLs were robust enough that they were detected in the less intensive (one‐fourth the labor and resources) Arkansas trials, where tillers were counted from two single‐plant replications just twice, at 6 wk after planting and after heading. The three loci associated with both TN and PN are the TN loci most likely to increase rice yield, and the markers presently found linked to them can be used for marker assisted breeding.

Covariation among Root Biomass, Shoot Biomass, and Tiller Number in Three Rice Populations

“…This indicates that, in spite of expected differences in age and size of individual tillers per plant, the elongation of the tallest tiller per plant (whether it includes leaf length or not) drives SB/TN more than either SB or TN alone. It is worth noting that, although Sd1 increases mature plant height over sd1 (Pinson and Jia, 2016), at the 6‐wk plant stage measured herein, neither shoot nor collar height differed significantly between the Sd1 and sd1 KZ‐RILs ( p v alues ≥ 0.075, Table 3). Although one might expect TN, culm elongation (collar height), and leaf length (included in shoot height) to all be contributing to and thus correlated with SB, the heatmap analyses show closer association between SB and TN than between SB and either shoot height or collar height, with the exception of the Sd1 KZ‐RIL subpopulation.…”

“…† Location of TN‐QTL among RILs derived from ‘Kaybonnet‐ lpa‐1 ’ × ‘Zhe733’ (KZ‐RILs) are per Pinson and Jia (2016); TN‐QTL among the ‘Lemont’ × ‘TeQing’ RILs (LT‐RILs) are per Pinson et al (2015).…”

“…The first population in this study was a set of RILs derived from ‘Kaybonnet‐ lpa‐1 ’ × ‘Zhe733’ (KZ‐RILs) (Rutger and Tai, 2005), in which five TN‐QTL had been previously mapped using data from two independent replicated studies, one conducted with potted plants grown in a Texas greenhouse (three replications, three plants each), and the other grown in Arkansas (two single‐plant replications) (Pinson and Jia, 2016). The data provided five replications across two greenhouse environments with which to select subgroups of RILs based on their consistently exhibiting high TN or low TN.…”

“…Plant growth traits for the present study were observed under greenhouse conditions, where key environmental factors, such as planting depth, air and water temperatures, water depth, and plant spacing, could be controlled. Potted plant growth procedures were patterned after those used previously for rice tillering observation (Jaffuel and Dauzat, 2005) and TN‐QTL mapping (Pinson et al, 2015; Pinson and Jia, 2016), and they are described in more detail per study in the two section below. All plant evaluations for this study were conducted in the same greenhouse at the Dale Bumpers National Rice Research Center located in Stuttgart, AR, during 2016 to 2017.…”

“…Three replications of FR‐RILs (now F 10 ) plus the two parents were planted in a randomized complete block design on 17 Feb. 2017, following the plant growth procedures used in prior TN studies (Pinson and Jia, 2016). Each replication contained one plant per FR‐RIL plus one plant per parental line, grown as one plant per pot, with each replication contained within a large tub 1.2 × 2.5 m in area and 0.3 m deep.…”