玉米杂交组合茎秆抗倒伏的生理机制研究

Increasing plant density is one of the most effective means to improve maize yield in China and the world in recent years. However, stalk lodging limits yield seriously under close planting. Enhancement of biomechanical stalk strength is a key method to decrease lodging for close planting high-yield in maize production. This project focuses on the study of the changes in cellulose and lignin content of maize stalk, by using various density-tolerant maize cultivars and their parental inbred lines. The relationship between cellulose and lignin accumulation with mechanical strength of the basal internodes will be study under the different planting density and shading treatments with various maize hybrid combinations. The difference of the key enzymes activities and the amounts of hormones during the cellulose and lignin synthesis will be determined, and then to reveal the influencing mechanisms of plant density and shading on activities of key enzymes and the amounts of hormones during cellulose and lignin synthesis. We will clarify the outside (environment and cultivation practices) and inside (genetic) factors of the determining mechanisms and the regulation pathway of the stalk lodging resistant strength. This study will provide theoretical bases for breeding stiff stalk lodging resistance maize cultivars, and help for improving maize yield under high planting density in Xinjiang.

增加种植密度是近年来我国乃至世界玉米大面积高产的最有效途径，而玉米密植后倒伏问题严重制约了单产的突破，增强茎秆抗倒伏强度是解决玉米密植高产的关键。本项目选用不同耐密性品种及其亲本自交系为材料，采用不同种植密度和人工遮光相结合的试验方法，从遗传背景差异、种植密度差异、受光环境差异等角度，研究玉米茎秆结构性物质纤维素和木质素的变化规律，探讨玉米茎秆基部节间纤维素、木质素合成代谢与茎秆强度形成的相互关系，明确不同抗倒伏能力的品种及亲本茎秆纤维素、木质素合成过程中关键酶活性及激素含量的差异；揭示种植密度、遮荫处理对茎秆纤维素、木质素代谢关键酶活性和激素含量的影响机理；阐明茎秆强度形成的内在（遗传）和外在（环境和措施）影响因素和调控途径。研究结果将为玉米耐密坚秆品种选育提供理论依据，并为新疆玉米进一步挖掘密植增产潜力提供技术支撑。

本项目主要从以下几方面开展了玉米杂交种及亲本茎秆结构性物质积累及代谢与茎秆强度形成机理的研究：.1. 玉米基部节间穿刺强度（RPS）均呈“S”曲线变化规律，在籽粒建成期（R2）达到峰值。杂交种基部节间穿刺强度均显著高于其父、母本，表现较高杂种优势指数（>100%）；抗倒伏能力较强的品种田间倒伏率均低于其父、母亲本。倒伏率与穿刺强度呈极显著负相关。.2. 玉米茎秆硬皮组织厚度、表皮机械组织厚度及大小维管束数目及面积均随种植密度增加而显著降低，杂种优势指数也明显降低。茎秆穿刺强度与硬皮组织厚度、表皮机械组织厚度和层数呈极显著正相关，与茎秆维管束数目及面积不相关性；茎秆弯曲强度(BS)与茎秆表皮机械组织、小维管束数目及面积均呈极显著正相关。.3. 玉米茎秆木质素和纤维素积累均随密度增加而降低。木质素在乳熟期（R3）达到峰值，纤维素在籽粒建成期（R2）达到峰值。杂交种茎秆木质素含量显著高于父本自交系，高于或接近其母本自交系，杂种优势指数较高。杂交种纤维素含量显著高于父本，表现出显著的超父优势，超母优势方面在品种间、密度间有一定差异。玉米基部节间木质素积累量和纤维素与穿刺强度极显著正相关。.4. 玉米茎秆木质素合成相关酶活性（PAL、TAL、CAD和POD）和纤维素合成相关酶（SS：蔗糖合成酶；SPS：蔗糖磷酸合成酶）均随种植密度的增加而降低。各个相关酶对茎秆木质素和纤维素合成产生作用时期不同。如PAL在生育前期（V9-VT）与木质素积累呈极显著相关，TAL在仅在生育后期（VT）与木质素积累关系密切，POD和CAD酶活则在生育中、后期（V15-VT）时期对木质素积累贡献较大。作为纤维素生物合成的关键酶，SS活性在纤维素快速积累期的前期（V6-V15）品种间差异较大，SPS活性在纤维素快速积累期中、后期（V12-VT）起决定作用。.5. 玉米茎秆中IAA、ABA和ZT含量呈不规则变化，峰值出现时间也不同。杂交种与父、母亲本间变化规律也不一致。IAA和ABA含量杂种优势指数较低；而ZT含量超亲优势和杂种优势指数均较高。初步分析得出，玉米茎秆中IAA含量与木质素、纤维素积累呈极显著正相关，ABA含量与木质素、纤维素含量呈极显著负相关，ZT与木质素积累呈显著正相关，而与纤维素积累关系不密切。