Effects of Foliar Application Uniconazole on Culm Morphological Characters,Anatomical Traits and Stem Lodging Resistance of Hybrid Indica Rice Under Low Light Stress
[Objective]The objective of current study was to investigate the regulation mechanism of endogenous hormones,culm anatomical and morphological traits and its relationship with lodging resistance of hybrid indica rice as affected by foliar application uniconazole under shading condition.The study results could provide theoretical basis and technical support for stable and abundant hybrid indica rice yield and emergency chemical regulation cultivation under poor light stress in Sichuan Basin.[Method]A split-split plot field experiment was carried out in Yongchuan,Chongqing from 2018 to 2019.Shading was selected as the main plots,namely,normal light treatment(NL)and shading treatment with decreased incident light by 50%(S).The foliar application uniconazole levels were used as splits-plots,and three uniconazole levels were set:0(U0),40 mg·L-1(U40),and 80 mg·L-1(U80),and the varieties were used as split-split plots,namely Yuxiang203(YX203)and Cliangyouhuazhan(CLYHZ),respectively.The study focused on analyzing the effects of foliar application uniconazole on stem lodging resistance of hybrid indica rice plant under shading condition,and further investigating the changes of culm morphological,anatomical traits and endogenous hormones and its relationship with stem mechanical strength.[Result]Shading and uniconazole treatments had significant effects on culm morphological and anatomical traits,changes of endogenous hormones and stem lodging index(LI)and its physical parameters in two hybrid indica rice varieties.Compared with NL,S treatments significantly raised LI owing to significant reduction of breaking resistance(M),even though bending moment by whole plant(WP)also decreased,especially for YX203.Further,S treatments significantly lowered thickness of mechanical tissue,area of small and large bundle vascular in basal culm internode.And,cell width was decreased slightly,but ratio of cell length to cell width was increased to a certain extent,thus reduced culm wall thickness and stem mechanical strength consequently.Under shading stress,foliar application uniconazole significantly decreased stem LI of two hybrid indica rice varieties,which attributed to lower WP and higher M values,especially for YX203.Foliar application uniconazole reduced plant height and gravity center height by shorter length of lower internodes.And further,endogenous hormones including GA1+3 and IAA content during culm formation stage was declined,induced reduction of cell length and ratio of cell length to cell width and thereby,contributed to shorter lower internodes.Besides,endogenous hormones Z+ZR and IP+IPA content were increased during culm early development,the cells size showed smaller and denser,cell layer of mechanical tissue and cell number of bundle vascular sheath were also increased,and thus improved small and larger bundle vascular number and area and stem mechanical strength.The correlation analysis showed that cell length,ratio of cell length to cell width,thickness of mechanical tissue and area of small and large bundle vascular were significantly and negatively correlated to LI,but positively correlated to M.The trend were consistent in both YX203 and CLYHZ.[Conclusion]Foliar application uniconazole declined cell length,ratio of cell length to cell width and length of basal internodes primarily owing to reduction of GA1+3 and IAA content,and increased cell layer of mechanical tissue,cell number of bundle vascular sheath and cell density in parenchyma tissue by increasing Z+ZR and IP+IPA content,and raised thickness of mechanical tissue,area of small and large bundle vascular and thereby,improved stem mechanical strength and lodging resistance of hybrid indica rice under poor light stress.
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