Abstract: In this study, pot experiments were performed and super hybrid early rice(Ganxin 203) and late rice(Wufengyou T025) were selected as the material. During panicle differentiation initiation stage no drought in earlier stage and no floods in later stage(control, CK), mild drought in earlier stage and no floods in later stage(T1), severe drought in earlier stage and no floods in later stage(T2), no drought in earlier stage and mild floods in later stage(T3), no drought in earlier stage and severe floods in later stage(T4), severe drought in earlier stage and mild floods in later stage abrupt alternation(T5), severe drought in earlier stage and severe floods in later stage abrupt alternation(T6), mild drought in earlier stage and mild floods in later stage abrupt alternation(T7), mild drought in earlier stage and severe floods in later stage abrupt alternation(T8) were set. While the indices of the yield and its components, dry matter accumulation and distribution and net photosynthetic rate(Pn) were investigated. The results showed that, (1) the yield per plant in super hybrid early and late rice was decreased in different degrees under “drought”, “flood” and “drought-floods abrupt alternation”. Compared with CK, the early rice T1, T2, T3, T4, T5, T6, T7 and T8 yield per plant were decreased by 8.89%, 21.42%, 8.33%, 12.04%, 19.65%, 31.23%, 15.39% and 17.29%, respectively. The late rice were decreased by 6.21%, 15.06%, 7.77%, 11.53%, 17.40%, 20.85%, 13.46% and 11.70%, respectively. The yield of T2 and T6 treatments in early and late rice was decreased more, especially the yield of T6 treatment was largest decline, it was shown that only mild drought or mild floods on yield were less affected, but only severe drought or severe floods on yield were relatively large affected, and severe drought was greater affected than severe floods on yield. As for rice plants treated with severe drought in earlier stage and severe floods in later stage abrupt alternation, a certain degree of superimposition and reduction effect was existed. In the yield components, the main reasons for the yield decreased by effective panicles per plant, number of grains per panicle, seed setting rate and secondary branch number. The effects of yield and yield components were roughly the same among treatments. (2) Compare with CK, stem and leaf dry mass were decreased in different degrees in early and late rice under “drought”, “flood” and “drought-floods abrupt alternation”. Among the early and late rice at mature stage, the panicle dry mass of T6 treatment decreased by 33.40% and 19.88%, respectively, compared with CK, and the panicle shape becomes smaller. (3) The leaf chlorophyll content(SPAD value) in early and late rice was decreased under “drought”, “flood” and “drought-floods abrupt alternation”. SPAD value of T6 treatment in early and late rice were decreased remarkably, and with CK has a significant difference. (4) Leaf Pn of T6 treatment in early and late rice was the lowest, decreased by 37.57% and 10.17%, respectively, compared with CK. The results of the study were illustrated that severe drought in earlier stage and severe floods in later stage abrupt alternation had the maximum influence on panicle dry mass and total dry mass at mature stage in early and late rice, and severe drought in earlier stage and severe floods in later stage abrupt alternation showed a superposition damage effect.

Key words: Double-season super hybrid rice, Panicle differentiation stage, Drought-floods abrupt alternation, Yield, dry matter, Photosynthetic rate