Effects of stubble height of the main crop on source-sink characteristics and assimilates transportation in ratooning rice.

The characteristics of source,sink and flow of ratooning rice with different stubble heights of the main crop were studied with eight rice varieties as materials.According to yield of ratooning rice with different stubble heights of the main crop,the eight varieties were classified into three ratooning types,such as high-stubble type(HST),low-stubble type(LST) and high/medium-stubble type(HMST).Decline of the stubble height resulted in decreased number of effective panicles and increased grain number per panicle in ratooning rice,especially for the grain number per panicle in ratooning rice of LST varieties.The leaf area index in ratooning rice of HST and HMST varieties was the highest under the high stubble treatment(40 cm),whereas that in ratooning rice of LST varieties increased with the decline of the stubble height.The leaf photosynthetic rates from full heading to 20 days after full heading in ratooning rice of HST varieties were higher under the medium(20 cm) or high(40 cm) stubble treatments,whereas the leaf photosynthetic rates at the full heading stage in ratooning rice of HMST and LST varieties were higher under the high stubble treatment and those at 10 days and 20 days after full heading were higher under the medium(20 cm) or low(10 cm) stubble treatments.The crop growth rates of ratooning rice of HST varieties were the highest under the high stubble treatment,whereas those of HMST and LST varieties were the highest under the low or medium stubble treatments.The activity of catalase in rachis branches of ratooning rice of HMST and LST varieties improved with declining stubble height,whereas a contrary trend was observed for HST ones.The transport rates of carbohydrate in stems and sheathes of ratooning rice of HST varieties were higher under the high stubble treatment,and those of LST ones were higher under the low and medium stubble treatments.These results indicate that the effect of stubble height of the main crop on characteristics of source,sink and flow of ratooning rice were closely related to ratooning types of rice varieties.