Radiation Use Efficiency and Source‐Sink Changes of Super Hybrid Rice under Shade Stress during Grain‐Filling Stage

Core Ideas Super hybrid and regular hybrid varieties differed in their response to shade stress.Apparent exportation, apparent export ratio, and apparent transformation ratio significantly increased under shade stress.Maintaining higher radiation use efficiency and daily biomass production during grain‐filling stage may alleviate yield loss under shade stress. Continuous cloudy weather during grain‐filling stage has induced a significant rice (Oryza sativa L.) yield loss. Field experiments were conducted to investigate the effects of shade stress on radiation use efficiency (RUE), biomass production, and grain yield in two consecutive years by shading from flowering to maturity using super hybrid rice (SHR) varieties (Liangyoupeijiu, Yliangyou900) and an ordinary hybrid rice (OHR) variety (Shanyou63). The shading environment was created with shade nets above the rice canopy to reduce light intensity by 40%. Grain yield in SHR was reduced by 48.0% under shade stress, which was significantly higher than OHR (30.3%). Seed set percentage and grain weight were the key factors that determined grain yield under shade stress after flowering. Seed set percentage decreased by 50.1% in SHR and 23.8% in OHR. Under shade stress total dry weight in SHR decreased by 32.4 and 26.3% in ordinary rice varieties. Mean apparent exportation (AE), apparent export ratio (AER), and apparent transformation ratio (ATR) of these varieties increased by 46.1, 45.7, and 227% respectively, under shade stress across years. The difference in intercepted percentage between shade stress and non‐shaded conditions was insignificant, but RUE was significantly affected by shade stress. Radiation use efficiency in SHR decreased by 28.5 and 22.2% in OHR. There were very significantly (P < 0.01) positive linear relationships between RUE, daily biomass production, and grain yield during grain‐filling stage. Our study suggests that higher RUE and daily biomass production during grain‐filling stage may alleviate yield loss under shade stress.