A better root morpho-physiology after heading contributing to yield superiority of japonica/indica hybrid rice

Abstract Grain yield superiority of japonica/indica hybrid rice (JIHR) over japonica inbred rice (JIR) and indica hybrid rice (IHR) was reported, and some shoot traits underlying high yield of JIHR were identified, like shoot stay-green traits after heading. To date, little information has focused on root trait differences among JIHR, JIR and IHR. Besides, improved shoot stay-green traits after heading of JIHR might indicate better root morpho-physiological traits after heading compared with JIR and IHR, considering the interdependent relationship between root and shoot. In this study, two JIHR, two JIR, and two IHR were planted in 2014 and 2015 at Ningbo, and in 2015 and 2016 at Yangzhou, China. JIHR showed longer total growth period especially the period from heading to maturity and higher grain yield per day, and 5.6–19.8% higher grain yield compared with JIR and IHR across two years at two sites. JIHR had consistently higher root and shoot biomass at heading and maturity at two sites compared with JIR and IHR. Higher root length and root volume, and more roots in the 11–30 cm soil depth at heading and maturity of JIHR over JIR and IHR were observed across years and sites. JIHR had not only higher leaf SPAD value and leaf photosynthetic rate, but also higher root bleeding rate and root oxidation activity during grain filling, compared with JIR and IHR. JIHR had lower reduction rate of root biomass, length, volume, bleeding rate, and oxidation activity from heading to maturity than JIR and IHR at two sites. Root length and root volume were correlated positively (P