抄録
Photosynthetic activity of flag leaves and dry matter production during the grain filling stage of Vietlai 20 (VL20), a Vietnamese hybrid rice variety, were examined and compared to those of its maternal cultivar (103S) and paternal cultivar (R20) under standard nitrogen (SN) and low nitrogen (SN) conditions. The results showed that the above-ground dry matter weight (DW) was not significantly different between VL20 and 103S under the LN condition. Also, there was no difference in the DW between VL20 and R20; while, VL20 exhibited a higher rate of panicle dry weight increase (PDW) than R20 under both SN and LN conditions. Because 103S is a thermo-sensitive genic male sterile line, PDW was negligible in 103S during maturity in the present experiment. With a restriction in N supply, the maximum CO2 exchange rate (CERmax), flag leaf nitrogen content (FLNC) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content decreased in VL20 and R20. However, VL20 exhibited a higher sustainability in both duration of grain filling and response to N deficiency in terms of CERmax value, FLNC and Rubisco content than R20. VL20 also showed significantly a higher value of quantum yield efficiency of PSII (ΦPSII) and lower value of non-photochemical quenching (NPQ) than R20 under the LN condition. Although the chlorophyll (Chl) content was not significantly different between VL20 and R20, the ratio of Chl/Rubisco was lower in VL20 than in R20 under the LN condition. These results indicated that the high FLNC and Rubisco content, and relatively low Chl/Rubisco ratio would result in a high photosynthetic rate and ΦPSII value in the F1 hybrid during the grain filling stage under the restriction of N supply.
