Effects Of Light Condition During Grain-filling Stage Of Main Crop On Ratooning Ability Of Low-stubble Ratoon Rice In Guangdong Province

Ratoon rice is of great significance in reducing rice planting costs,improving economic benefits,and ensuring national food security.Low-stubble ratoon rice has a long growth duration and large yield potential and is the main direction for ratoon rice development in Guangdong province,China.However,unstable ratoon bud emergence and high missing hill rate in the ratoon crop are prominent problems faced by low-stubble ratoon rice production.Previous studies have shown that the light transmission ratio of the main crop rice during grain-filling stage is an important factor affecting ratooning ability of rice.However,it is not clear whether light intensity or light quality or both affect rice ratooning ability,and whether there is any difference in the impact of light at different grain-filling stages on ratooning ability.Studying the relationship between rice ratooning ability and light conditions and clarifying the impact of light intensity and quality on rice ratooning ability and its key periods can provide theoretical basis and technical support for improving rice ratooning ability and achieving high and stable yield of ratoon rice.Two experiments were conducted in this study.Experiment 1 and Experiment 2 were conducted at Dafeng Experimental Station of Guangdong Academy of Agricultural Sciences in 2022.In Experiment 1,randomized block design were used and there were 12treatments consisting of two cultivars[Meixiangzhan 2（MXZ2）and Qingxiangyou 19xiang（QXY19X）],two nitrogen rates(0 and 120 kg N ha^-1)and three transplanting spacings（40 cm x 20 cm,20 cm x 20 cm and 10 cm x 20 cm）.Light intensity at the base of the canopy（LI_b）during grain-filling stage,light quality at the base of the canopy（R:FR）at 15 days after heading（RFR_b）,light transmission ratio（LTR）,leaf area index（LAI）and root bleeding of the main crop,grain yield and yield components of both main and ratoon crop,as well as the ratooning hill rate,maximum ratooning rate,and final ratooning rate were measured.In Experiment 2,the effects of shading at different grain-filling stages of the main crop on ratooning ability were investigated.There were four treatments,i.e.no shading and shading in the early,middle,and late grain-filling stages of the main crop.The test material was QXY19X grown under conventional and dense planting densities.The main results are as follows:1.Different nitrogen fertilizer and planting density treatments have significant effects on LI_band RFR_b as well as grain yield and ratooning ability.Under different treatments,grain yield of main crop and ratoon crop was 4.57～7.53 t ha^-1 and 2.52～3.69 t ha^-1 for MXZ2,and 5.63-8.85 t ha^-1 and 1.68-3.16 t ha^-1 for QXY19X,respectively.There were significant differences between treatments in LI_b,RFR_b,LTR,LAI,root bleeding per stem,and stem and sheath weight per stem of the main crop rice at the grain-filling stage.2.Ratooning ability is closely related to LI_b.For MXZ2,LI_b was significantly and positively related to the ratooning hill rate（r=0.480,P<0.05）and the final ratooning rate（r=0.768,P<0.01）.The RFR_b was significantly and positively correlated with the final ratooning rate（r=0.672,P<0.01）.For QXY19X,LI_bwas significantly and positively correlated with the ratooning hill rate（r=0.657,P<0.01）,the maximum ratooning rate（r=0.700,P<0.01）,and the final ratooning rate（r=0.552,P<0.05）.The RFR_b was significantly and positively correlated with the ratooning hill rate（r=0.550,P<0.05）and the maximum ratooning rate（r=0.710,P<0.01）.3.The shading experiment showed that the light condition at different grain-filling stages of the main crop had different effects on ratooning ability.Shading during the early grain-filling stage had no significant effect on the ratooning ability of rice,while shading during the middle and late grain-filling stages of the main crop significantly reduced the ratooning hill rate,the maximum ratooning rate,and the final ratooning rate.The performance of the two varieties was consistent.The middle and late grain-filling stages of the main crop are the main stages when light condition affects the ratooning ability of low-stubble ratoon rice.4.The maximum ratooning rate was significantly and positively correlated with the root bleeding per stem during grain-filling stage of main crop（r=0.626,P<0.01 for MXZ2;r=0.620,P<0.01 for QXY19X）,and so did the ratooning hill rate and the final ratooning rate.The root bleeding per stem was significantly and positively correlated with the LI_b（r=0.518,P<0.05 for MXZ2;r=0.693,P<0.01 for QXY19X）and RFR_b（r=0.539,P<0.05for MXZ2;r=0.632,P<0.01 for QXY19X）,indicating that LI_b may have affected the ratooning ability of rice by changing root activity.In summary,the light intensity and light quality have a significant impact on the ratooning ability of rice,with the middle and late grain-filling stages being more important.Light may affect the ratooning ability by altering the root activity.Improving plant architecture and adopting a wide-row and narrow-plant planting method to improve light transmission ratio,light intensity and R:FR,as well as raising root activity might be effective approaches to improving the ratooning ability of low-stubble ratoon rice.The results could be helpful for the high and stable yield cultivation of low-stubble ratoon rice.