Eco-physiological evaluation of Stele Transversal Area 1 for rice root anatomy and shoot growth

Larger 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.