Basal internode elongation of rice as affected by light intensity and leaf area

Short basal internodes are important for lodging resistance of rice (Oryza sativa L.). Several canopy indices affect the elongation of basal internodes, but uncertainty as to the key factors determining elongation of basal internodes persists. The objectives of this study were (1) to identify key factors affecting the elongation of basal internodes and (2) to establish a quantitative relationship between basal internode length and canopy indices. An inbred rice cultivar, Yinjingruanzhan, was grown in two split-plot field experiments with three N rates (0, 75, and 150 kg N ha⁻¹ in early season and 0, 90, and 180 kg N ha⁻¹ in late season) as main plots, three seedling densities (16.7, 75.0, and 187.5 seedlings m⁻²) as subplots, and three replications in the 2015 early and late seasons in Guangzhou, China. Light intensity at base of canopy (L_b), light quality as determined from red/far-red light ratio (R/FR), light transmission ratio (LTR), leaf area index (LAI), leaf N concentration (NLV) and final length of second internode (counted from soil surface upward) (FIL) were recorded. Higher N rate and seedling density resulted in significantly longer FIL. FIL was negatively correlated with L_b, LTR, and R/FR (P < 0.01) and positively correlated with LAI (P < 0.01), but not correlated with NLV (P > 0.05). Stepwise linear regression analysis showed that FIL was strongly associated with L_b and LAI (R² = 0.82). Heavy N application to pot-grown rice at the beginning of first internode elongation did not change FIL. We conclude that FIL is determined mainly by L_b and LAI at jointing stage. NLV has no direct effect on the elongation of basal internodes. N application indirectly affects FIL by changing LAI and light conditions in the rice canopy. Reducing LAI and improving canopy light transmission at jointing stage can shorten the basal internodes and increase the lodging resistance of rice.