Abstract
ABSTRACTLarger stele size with greater xylem area or endodermis thickness in rice roots may lead to higher plant water status and maintain yield. Sta1-NIL, a near-isogenic line of IR64 introgressed with Stele Transversal Area 1 (Sta1), a quantitative trait locus controlling stele transversal area (STA) was investigated together with IR64 for their root anatomy and physiological parameters, at seedling, heading and maturity stages in greenhouse and fields of water deficit and well-watered conditions in 2017 and 2018. Combined analysis of STA from nine observations of overall four experiments showed that STA was increased by 7% (35,400 to 37,800 μm2) by the introduction of Sta1 into IR64. Total late metaxylem area also increased by 6% (5,840 to 6,180 μm2), which came mainly from its single area rather than its number, whereas small increase in endodermis thickness was also noted. Genotype x observation for STA was marginal, but Sta1-NIL had larger STA under water deficit environments. Sta1-NIL also maintained higher mid-day leaf water potential (−2.34 ± 0.3 MPa) than IR64 (−2.57 ± 0.3 MPa). Meta-analysis of seven experiments under 14 environments showed tendency of the positive effect of Sta1 on grain yield increment (579 to 604 g m−2), which came from the increment of harvest index. This study indicated the importance of wider stele size for maintenance of higher plant water status and yield across different water regimes.
Highlights
Rice is a semi-aquatic plant with a shallow and thin root system compared with dryland crops such as wheat and corn
By the introduction of Stele Transversal Area 1 (Sta1) into IR64, stele transversal area (STA) increased by 7%, accompanied by increase in LMXA by 6% and endodermis thickness (ETH) by 3% based on the combined analysis in all the data in 2 years of the overall four experiments that included both well-watered and water-deficit environments (Table 3; Table S1)
Increased LMXA could be mainly contributed from its single area rather than its number as its single area was marginally increased by 4%, but not the late metaxylem number (LMXN) (Table 3)
Summary
Rice is a semi-aquatic plant with a shallow and thin root system compared with dryland crops such as wheat and corn. Investigation of rice root traits and their improvement have been less studied compared to aboveground traits because of difficulty in phenotyping (Voss-Fels, Snowdon & Hickey, 2018). Studies of root anatomical traits are less reported probably due to its tedious and time-consuming phenotyping (Atkinson & Wells, 2017; Burton, Williams, Lynch & Brown, 2012; Chopin, Laga, Huang, Heuer & Miklavcic, 2015; Uga, Okuno & Yano, 2008). Genotypic variation in stele size has been reported in rice (Kondo, Aguilar, Abe & Morita, 2000; Terashima, Hiraoka & Nishiyama, 1987; Uga et al, 2008). Uga et al (2009) found larger transversal areas of the stele and late metaxylem in upland japonica than indica and lowland japonica rice among Asian rice accessions Traditional upland japonica cultivars showed the largest stele, stele ratio, and late metaxylem vessel diameters, followed by modern upland japonica, aus and indica cultivars (Kondo et al, 2000). Uga et al (2009) found larger transversal areas of the stele and late metaxylem in upland japonica than indica and lowland japonica rice among Asian rice accessions
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