薛軍，王克如，謝瑞芝，勾玲，張旺鋒，明博，侯鵬，李少昆

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玉米生長(zhǎng)后期倒伏研究進(jìn)展

薛軍１，王克如１，謝瑞芝１，勾玲２，張旺鋒２，明博１，侯鵬１，李少昆１

（1中國(guó)農(nóng)業(yè)科學(xué)院作物科學(xué)研究所/農(nóng)業(yè)部作物生理生態(tài)重點(diǎn)實(shí)驗(yàn)室，北京 100081；2石河子大學(xué)農(nóng)學(xué)院/新疆生產(chǎn)建設(shè)兵團(tuán)綠洲生態(tài)農(nóng)業(yè)重點(diǎn)實(shí)驗(yàn)室，新疆石河子 832003）

倒伏是玉米生產(chǎn)中普遍存在的問(wèn)題。傳統(tǒng)生產(chǎn)中玉米一般在生理成熟期收獲，前人關(guān)于倒伏研究也多集中在生育前期莖稈發(fā)育過(guò)程或者是生理成熟前的某一階段，而對(duì)生理成熟后倒伏研究較少。玉米機(jī)械粒收一般在生理成熟后2—4周進(jìn)行，倒伏將會(huì)增加機(jī)械粒收過(guò)程中的產(chǎn)量損失，降低籽粒品質(zhì)，使收獲難度加大，收獲效率以及玉米種植效益明顯降低，成為制約玉米種植密度進(jìn)一步提高和機(jī)械粒收技術(shù)發(fā)展的重要因素。對(duì)此，本文從玉米生育后期植株的衰老生理及其影響因素角度進(jìn)行綜述，提出增強(qiáng)玉米后期抗倒伏能力的措施與建議。分析表明，玉米生育后期植株自然衰老將導(dǎo)致葉片、莖稈和根系活力下降，使莖稈含水量、可溶性糖、半纖維素及總結(jié)構(gòu)性碳水化合物含量均降低，細(xì)胞壁變薄、細(xì)胞間縫隙變大；同時(shí)，莖稈和根系PAL、POD和PPO酶活性下降，抗病能力減弱；莖腐病病原菌產(chǎn)生的細(xì)胞壁降解酶分解細(xì)胞壁中的纖維素，降解寄主細(xì)胞，孢子迅速萌發(fā)形成菌絲并進(jìn)入表皮細(xì)胞、皮層和維管束組織，加速莖稈組織失水干縮過(guò)程，植株空心變軟甚至腐爛，莖稈質(zhì)量下降。而基于密植高產(chǎn)機(jī)械粒收技術(shù)需求的增密種植、田間站稈籽粒脫水會(huì)加速并延長(zhǎng)玉米衰老進(jìn)程，使莖稈質(zhì)量和抗病能力進(jìn)一步下降，導(dǎo)致生理成熟后的倒伏風(fēng)險(xiǎn)加大。為有效控制倒伏、加速我國(guó)玉米密植高產(chǎn)機(jī)械粒收技術(shù)的推廣，建議：（1）增強(qiáng)玉米生育后期莖稈衰老和倒伏的理論研究；（2）加強(qiáng)玉米抗倒種質(zhì)創(chuàng)制，選育早熟、耐密植、籽粒脫水快、抗逆性強(qiáng)、適宜機(jī)械粒收的品種；（3）通過(guò)構(gòu)建優(yōu)質(zhì)土壤耕層，集成宜機(jī)收品種、合理密植、肥水科學(xué)運(yùn)籌、化學(xué)調(diào)控和病蟲(chóng)害綜合防控等關(guān)鍵技術(shù)，創(chuàng)制高質(zhì)量健康群體，提高生育后期莖稈的抗倒伏能力；（4）根據(jù)各地氣候、生態(tài)條件，因地制宜制定降低玉米生育后期倒伏風(fēng)險(xiǎn)的應(yīng)對(duì)措施。

玉米；莖稈衰老；倒伏；機(jī)械粒收；莖腐病

倒伏是玉米生產(chǎn)中常見(jiàn)的現(xiàn)象。玉米倒伏可分為莖折和根倒，其中，莖稈在穗位節(jié)或穗位節(jié)以下的折斷稱(chēng)為莖折，莖稈與垂直線(xiàn)大于一定角度（30°或45°）而莖稈不發(fā)生折斷稱(chēng)為根倒[1-2]。玉米根倒多發(fā)生在吐絲期之前的暴雨加大風(fēng)天氣，吐絲期之后玉米以莖折為主，且多發(fā)生在穗下基部節(jié)間[3]。生理成熟前玉米發(fā)生倒伏后影響了籽粒灌漿速率，對(duì)產(chǎn)量影響較大[4]；生理成熟后倒伏對(duì)玉米產(chǎn)量形成影響較小，但是增加了機(jī)械粒收過(guò)程中的落穗量，降低了籽粒品質(zhì)，收獲難度加大，收獲效率以及玉米種植效益明顯降低[5-7]。玉米大面積倒伏后，農(nóng)戶(hù)人工撿拾果穗的成本往往高于果穗自身的價(jià)值[8-9]。國(guó)家標(biāo)準(zhǔn)“玉米收獲機(jī)械技術(shù)條件”（GB/T-21962-2008）中規(guī)定機(jī)械粒收的條件為田間植株倒伏率應(yīng)低于5%[10]。在我國(guó)玉米全程機(jī)械化發(fā)展的重要時(shí)期，分析玉米倒伏研究現(xiàn)狀及其對(duì)機(jī)械粒收的影響，探討影響玉米生育后期倒伏發(fā)生的關(guān)鍵因素及提高玉米抗倒能力的途徑與方法，對(duì)實(shí)施玉米密植高產(chǎn)機(jī)械化生產(chǎn)過(guò)程中抗倒品種的選育和栽培具有重要意義。

1 玉米倒伏研究現(xiàn)狀

前人從植株形態(tài)學(xué)、莖稈力學(xué)特性、莖稈解剖結(jié)構(gòu)與物質(zhì)積累分配、根系生長(zhǎng)特性、病蟲(chóng)害發(fā)生與危害、區(qū)域氣候生態(tài)特點(diǎn)、品種遺傳特性、種植密度、水肥管理及化學(xué)調(diào)控等方面對(duì)玉米倒伏問(wèn)題進(jìn)行了較為全面的研究。植株形態(tài)學(xué)的研究認(rèn)為，玉米基部節(jié)間較長(zhǎng)的植株具有較高的穗位和重心高度，倒伏風(fēng)險(xiǎn)大；相反，基部節(jié)間較短且粗壯的植株具有較強(qiáng)的抗倒伏能力[2, 5]。玉米莖稈力學(xué)特性、解剖結(jié)構(gòu)及物質(zhì)積累與分配的研究表明，莖稈力學(xué)強(qiáng)度，如莖稈外皮穿刺強(qiáng)度、壓碎強(qiáng)度和彎曲強(qiáng)度均與田間倒伏率呈顯著負(fù)相關(guān)[11-12]；而莖稈外皮機(jī)械細(xì)胞、機(jī)械組織和維管束是提供力學(xué)強(qiáng)度的結(jié)構(gòu)基礎(chǔ)[13]；莖稈中纖維素、木質(zhì)素和半纖維素等結(jié)構(gòu)性碳水化合物是形成機(jī)械細(xì)胞和機(jī)械組織的物質(zhì)基礎(chǔ)，其含量多少?zèng)Q定了玉米莖稈強(qiáng)度的高低[13-15]。根系研究表明，根系數(shù)量、總根體積、根與豎直方向夾角、根系直徑及根系垂直拉力（vertical root pulling resistance，VRPR）與倒伏密切相關(guān)[16-18]。在病蟲(chóng)危害方面，玉米螟和莖腐病是造成玉米倒伏的主要病蟲(chóng)害，其中，玉米螟通過(guò)鉆到莖稈內(nèi)部，蛀空莖稈，使玉米莖折率大幅增加[19-20]；玉米莖腐病病原菌產(chǎn)生細(xì)胞壁降解酶，分解細(xì)胞壁中的纖維素，降解寄主細(xì)胞（圖1）[21]；同時(shí)孢子迅速萌發(fā)成菌絲并從莖稈表面進(jìn)入表皮細(xì)胞、皮層和維管束組織，使莖稈組織失水干縮，空心變軟甚至腐爛，造成莖折[22-24]。玉米種植區(qū)生態(tài)環(huán)境條件對(duì)倒伏發(fā)生具有重要影響[25]。前人研究表明，降雨是我國(guó)黃淮海地區(qū)倒伏發(fā)生的主要脅迫因子[26]，抽雄前后的降雨加大風(fēng)可造成86%—99%的植株倒伏[27]。遺傳因素作為控制玉米倒伏的核心因素，也已表明，控制玉米倒伏性狀是由多個(gè)基因位點(diǎn)共同作用的結(jié)果；利用數(shù)量性狀位點(diǎn)（QTL）分析方法發(fā)現(xiàn)一些與節(jié)間伸長(zhǎng)、株高及莖稈穿刺強(qiáng)度相關(guān)的基因位于玉米的第3號(hào)染色體[28-30]。在栽培管理方面，增加種植密度后玉米莖稈會(huì)變的纖細(xì)，莖稈中纖維素、木質(zhì)素和半纖維素含量下降，穿刺強(qiáng)度降低，根系較小，倒伏風(fēng)險(xiǎn)增大[3, 15, 31]；合理的水肥及化學(xué)調(diào)控可以降低玉米莖稈基部節(jié)間伸長(zhǎng)速率，降低節(jié)間長(zhǎng)粗比、穗位高及株高，促進(jìn)節(jié)間干物質(zhì)積累及結(jié)構(gòu)形成，增強(qiáng)莖稈機(jī)械強(qiáng)度及抗倒伏能力[32-36]。

a：未感病的正常植株，b：中度感病組織；c：重度感病組織；CW：細(xì)胞壁

2 玉米生育后期植株衰老對(duì)莖稈質(zhì)量及倒伏的影響

關(guān)于倒伏問(wèn)題的研究以往多集中在玉米莖稈前期發(fā)育過(guò)程或生理成熟之前的某一個(gè)階段[2, 5, 11-36]，對(duì)生育后期和生理成熟后莖稈衰老及倒伏研究較少。而玉米生育后期植株衰老過(guò)程中莖稈會(huì)發(fā)生一系列變化，如莖稈失水、活性下降、碳水化合物分解、細(xì)胞壁降解、病蟲(chóng)害發(fā)生加重等，這些變化會(huì)影響玉米后期莖稈質(zhì)量，從而導(dǎo)致倒伏發(fā)生。

2.1 玉米生育后期植株衰老對(duì)莖稈質(zhì)量的影響

可溶性碳水化合物是莖稈結(jié)構(gòu)性碳水化合物合成的物質(zhì)基礎(chǔ)。玉米生育后期植株自然衰老，根系活性迅速下降，對(duì)水分和營(yíng)養(yǎng)物質(zhì)吸收能力降低；葉片衰老，光合能力顯著下降，產(chǎn)生的碳水化合物總量減少，分配到莖稈中的碳水化合物量下降[37]。同時(shí)，籽粒庫(kù)對(duì)莖稈中可溶性碳水化合物的拉力和莖稈自身的呼吸消耗，使生育后期莖稈可溶性碳水化合物含量逐漸下降。此外，與纖維素和木質(zhì)素相比，半纖維素穩(wěn)定性較差，生育后期半纖維素含量的下降也會(huì)導(dǎo)致莖稈中總結(jié)構(gòu)性碳水化合物含量降低[13]。在生育后期，莖稈中水分含量也是影響其機(jī)械強(qiáng)度的重要因素[15, 38]，Anderson等[23]認(rèn)為，玉米抽雄后莖稈含水量逐漸降低，并且莖稈髓部含水量與莖稈強(qiáng)度呈顯著正相關(guān)。Djorjevic等[39]認(rèn)為成熟期玉米莖稈含水量與倒伏率呈顯著負(fù)相關(guān)。因此，生育后期玉米莖稈衰老過(guò)程中的碳水化合物和水分含量降低使莖稈質(zhì)量下降。玉米生理成熟期至收獲階段，由于葉片蒸騰作用降低，加之根系迅速衰老，水分吸收能力會(huì)顯著降低，使莖稈含水量逐漸下降。Chen等[15]研究表明，在我國(guó)吉林地區(qū)，從8月30日至9月30日，玉米莖稈總碳水化合物降低31%—42%，含水率由77%—79%降低至52%—56%。

2.2 玉米生育后期衰老對(duì)莖稈抗病能力的影響

玉米生育后期莖稈衰老使植株抗病能力下降，病蟲(chóng)害易于發(fā)生。生育后期莖腐病是導(dǎo)致玉米倒伏發(fā)生的重要因素，植株抗莖腐病能力與莖稈含水率、生理活性及可溶性糖含量有關(guān)。Anderson等[23]認(rèn)為玉米生育后期莖稈髓部含水量高的植株莖腐病發(fā)生率較低；苯丙氨酸解氨酶（PAL）、過(guò)氧化物酶（POD）、多酚氧化酶（PPO）等抵抗病原微生物侵染的關(guān)鍵酶活性高的植株抗莖腐病能力強(qiáng)[40-42]；另外，莖腐病屬于低糖害病，莖稈總糖含量降低可引起莖稈髓組織衰退，增加玉米對(duì)莖腐病的敏感性[42-43]，而糖含量越高，對(duì)莖腐病的抗性越強(qiáng)[44]。玉米生育后期，自然衰老過(guò)程中莖稈和根系PAL、POD、PPO酶活性下降，同時(shí)莖稈水分散失和可溶性糖分解，均會(huì)導(dǎo)致植株抗莖腐病能力下降，莖腐病發(fā)生程度加重。此外，莖腐病病原菌產(chǎn)生的孢子又會(huì)堵塞維管束等疏導(dǎo)組織[21]，使植株的運(yùn)輸系統(tǒng)遭到破壞，進(jìn)一步加速植株衰老，在玉米莖稈衰老和莖腐病發(fā)生之間形成惡性循環(huán)。

2.3 玉米生育后期衰老對(duì)倒伏的影響

生育后期，玉米莖稈質(zhì)量和抗病能力的變化影響倒伏發(fā)生。玉米生育后期莖稈碳水化合物分解和水分含量下降導(dǎo)致細(xì)胞萎縮，細(xì)胞壁降解變薄，細(xì)胞之間縫隙加大，韌性降低，脆性增加，機(jī)械強(qiáng)度降低，倒伏風(fēng)險(xiǎn)加大[23, 39, 45]。Nolte[46]等研究表明，在美國(guó)俄亥俄州10月15日之后，每推遲一周，玉米倒伏率增加5%。同時(shí)，玉米生理成熟后，由于莖腐病引發(fā)的倒伏會(huì)逐漸上升，且上升幅度遠(yuǎn)高于生理成熟前。Thomison[47]等研究認(rèn)為在59 000株/hm2條件下，收獲期由10月中上旬推遲至11月中上旬時(shí)，田間莖腐病發(fā)生率由33%提高至85%，倒伏率由4%提高至23%；收獲期推遲至12月中上旬時(shí)，莖腐病高達(dá)100%，倒伏率達(dá)51%。

綜上，在玉米生育后期自然衰老過(guò)程中，莖稈碳水化合物含量和水分喪失使莖稈強(qiáng)度下降，田間倒伏風(fēng)險(xiǎn)上升；同時(shí)，生育后期根系和莖稈活性降低，莖稈中可溶性糖含量下降，導(dǎo)致莖稈抗病能力下降，莖腐病發(fā)生嚴(yán)重，而莖腐病發(fā)生又進(jìn)一步加快植株衰老。玉米莖稈衰老和莖腐病發(fā)生形成惡性循環(huán)，衰老加速，莖腐病發(fā)生率和發(fā)病程度加重，植株抗倒能力迅速下降，倒伏率顯著上升（圖2）。

圖2 生育后期玉米衰老和莖腐病對(duì)莖稈機(jī)械強(qiáng)度及倒伏的影響

3 玉米生育后期倒伏對(duì)機(jī)械粒收的影響

全程機(jī)械化是現(xiàn)代玉米生產(chǎn)的發(fā)展方向，當(dāng)前，機(jī)械粒收是我國(guó)玉米全程機(jī)械化生產(chǎn)中急需解決的關(guān)鍵環(huán)節(jié)[48]。增密種植與田間站稈籽粒脫水是機(jī)械粒收技術(shù)發(fā)展和推廣的重要措施[49]。以往我國(guó)玉米收獲以人工收獲和機(jī)械穗收為主，對(duì)倒伏問(wèn)題的研究多集中在生理成熟之前，生理成熟后田間站稈脫水至收獲階段的研究較少，而此階段發(fā)生的倒伏與增密種植和田間站稈時(shí)間密切相關(guān)，需要引起高度關(guān)注。

3.1 玉米倒伏對(duì)增密種植的影響

過(guò)去幾十年，世界范圍內(nèi)玉米單產(chǎn)水平的提高與種植密度的增加關(guān)系密切。與美國(guó)玉米種植密度及產(chǎn)量相比，我國(guó)玉米種植密度仍有很大的提升空間，增密種植仍將是未來(lái)玉米單產(chǎn)水平提升的重要途徑[49]。同時(shí)，機(jī)械粒收玉米品種要求成熟期略提早，而早熟品種生物量通常較小，通過(guò)增密種植，可以彌補(bǔ)單株產(chǎn)量較低帶來(lái)的產(chǎn)量損失[50]。但是增密種植在不同程度上增加了玉米植株間的競(jìng)爭(zhēng)壓力，造成冠層內(nèi)部光照不良，改變了個(gè)體和群體的結(jié)構(gòu)與功能，影響了玉米莖稈形態(tài)建成、碳水化合物積累與分配、莖稈解剖結(jié)構(gòu)、力學(xué)強(qiáng)度、根系形態(tài)與結(jié)構(gòu)等，增大倒伏風(fēng)險(xiǎn)[2-3, 16, 51]。增密種植也會(huì)影響玉米植株衰老進(jìn)程，使生育后期玉米莖稈質(zhì)量發(fā)生改變。盧霖等[52]研究表明，提高種植密度，植株葉片、根系和莖稈的活性降低，根系對(duì)水分和養(yǎng)分的競(jìng)爭(zhēng)加大，并且冠層內(nèi)部光照減弱，這些變化促使葉片和根系功能期縮短，衰老進(jìn)程加快。因此，高密度種植的玉米收獲期莖稈質(zhì)量變差和更容易發(fā)生倒伏。Thomison等[47]認(rèn)為，生理成熟后一定時(shí)間段內(nèi)，種植密度越高，莖稈質(zhì)量下降幅度越大，群體倒伏率增加趨勢(shì)也越明顯。此外，與低密度種植相比，密植條件下玉米植株個(gè)體之間距離變近，冠層內(nèi)部通風(fēng)透光條件變差，也有利于莖腐病病原菌和孢子傳播；加之玉米根系和莖稈中可溶性糖含量、生理活性均下降，抗莖腐病能力下降，不論是抗病品種還是易感病品種，莖腐病發(fā)病率均隨植株密度的增加而提高[53-54]。種植密度越高，推遲收獲后的莖腐病發(fā)病率和倒伏率也越高[47]。因此，玉米生育后期倒伏是限制種植密度進(jìn)一步提升的重要因素。

3.2 玉米倒伏對(duì)生理成熟后田間站稈脫水的影響

機(jī)械粒收要求玉米籽粒含水量控制在27%以下[55-56]，一般生理成熟后田間站稈自然脫水2—4周才能達(dá)到機(jī)械粒收的要求，推遲收獲后提高了莖稈倒伏風(fēng)險(xiǎn)。在田間站稈脫水階段，玉米雌穗重達(dá)到最大，莖稈受種植區(qū)大風(fēng)、降雨、莖稈碳水化合物變化等影響，莖稈衰老進(jìn)程加快，莖腐病發(fā)生率和發(fā)生程度顯著提高，導(dǎo)致莖稈強(qiáng)度降低，田間倒伏加重[47, 57]。Allen[58]等觀測(cè)到，在田間站稈脫水過(guò)程中，當(dāng)玉米籽粒含水量從25%降至15%時(shí)，倒伏率增加了42%。因此，玉米生理成熟至收獲期的倒伏問(wèn)題將會(huì)影響田間站稈籽粒脫水的時(shí)間，從而降低機(jī)械粒收玉米的籽粒品質(zhì)，增大高水分收獲籽粒的烘干成本。

總之，基于玉米密植高產(chǎn)機(jī)械化生產(chǎn)技術(shù)需求的增密種植和田間站稈籽粒脫水均會(huì)加速玉米生育后期莖稈衰老進(jìn)程，降低莖稈抗病能力，使莖稈質(zhì)量下降，倒伏風(fēng)險(xiǎn)加大。因此，玉米密植高產(chǎn)機(jī)械粒收生產(chǎn)技術(shù)的推廣和應(yīng)用對(duì)生育后期莖稈的抗倒伏能力提出了更高的要求。

4 提高玉米生育后期抗倒伏能力的措施與建議

與發(fā)達(dá)國(guó)家相比，我國(guó)玉米機(jī)械粒收起步晚，對(duì)生育后期和生理成熟后倒伏問(wèn)題關(guān)注不夠，制約了玉米密植高產(chǎn)機(jī)械粒收技術(shù)的推廣和發(fā)展。今后，需要加強(qiáng)倒伏問(wèn)題相關(guān)理論基礎(chǔ)研究，通過(guò)品種創(chuàng)制、栽培調(diào)控及因地種植改善生育后期玉米的抗倒伏能力，適期收獲，推進(jìn)玉米機(jī)械粒收和增密種植技術(shù)的發(fā)展。

4.1 加強(qiáng)倒伏問(wèn)題相關(guān)理論基礎(chǔ)研究，為抗倒伏技術(shù)創(chuàng)新提供依據(jù)

玉米生育后期和生理成熟后的倒伏問(wèn)題受基因型、環(huán)境和措施的共同作用，是一個(gè)復(fù)雜的過(guò)程，以往相關(guān)研究較為薄弱，今后需要組織開(kāi)展系統(tǒng)攻關(guān)，為品種創(chuàng)制、栽培調(diào)控提供依據(jù)。玉米莖稈后期活性是影響倒伏的重要因素，前人研究認(rèn)為保持玉米生育后期的持綠性有助于將莖稈活性和質(zhì)量維持在較高水平、降低倒伏風(fēng)險(xiǎn)[59-60]，然而后期持綠性高的植株往往不利于籽粒脫水，因此，需要進(jìn)一步研究玉米植株持綠性和籽粒脫水速率之間的關(guān)系，解決籽粒脫水和莖稈持綠抗倒之間的矛盾，為玉米站稈脫水過(guò)程保持高抗倒能力提供物質(zhì)基礎(chǔ)。

4.2 加強(qiáng)玉米抗倒種質(zhì)創(chuàng)制，選育適宜機(jī)械粒收品種

國(guó)內(nèi)外經(jīng)驗(yàn)證明，選育耐密植、適宜機(jī)械粒收品種是推廣機(jī)械籽粒收獲技術(shù)的關(guān)鍵。不同玉米品種籽粒脫水速率不同，生理成熟后莖稈水分下降和干物質(zhì)分解速率不同，抗莖腐病能力不同[47, 57]。因此，田間站稈持續(xù)時(shí)間和抗倒伏能力有明顯的差異。20世紀(jì)60—90年代，美國(guó)開(kāi)始大面積推廣機(jī)械粒收技術(shù)，同期開(kāi)展了大量玉米抗莖腐病、抗倒伏和適合機(jī)械粒收關(guān)鍵技術(shù)方面的研究。通過(guò)田間觀察、化學(xué)分析、解剖觀測(cè)、物理機(jī)械、病蟲(chóng)害誘導(dǎo)、高密度育種等手段選育出了一系列適合機(jī)械粒收的耐密、抗病、抗倒品種[61]。60多年來(lái)，我國(guó)玉米品種演替過(guò)程中抗倒伏能力逐漸提高，自20世紀(jì)80年代起重視緊湊型耐密品種的選育[62]。同時(shí)，我國(guó)也引進(jìn)了國(guó)外BSSS群體，選育出一些配合力高、抗倒性好的優(yōu)良自交系[63]。但是在玉米品種選育過(guò)程中，并沒(méi)有特意關(guān)注玉米生育后期，尤其是生理成熟后的倒伏問(wèn)題，品種抗倒伏能力的提高是單純追求產(chǎn)量目標(biāo)的附帶結(jié)果。今后應(yīng)以籽粒生產(chǎn)效益為導(dǎo)向，通過(guò)高密度育種、田間站稈觀察、分子設(shè)計(jì)等手段選擇后期青稈成熟、生理成熟期籽粒含水率低且耐密植的玉米品種，降低潛在倒伏風(fēng)險(xiǎn)。

4.3 構(gòu)建高質(zhì)量健康群體，減緩生育后期莖稈衰老進(jìn)程，提高植株抗倒伏能力

玉米生育前期高質(zhì)量莖稈是生育后期維持高抗倒伏能力的基礎(chǔ)。在選用適合機(jī)械粒收抗倒品種的基礎(chǔ)上，應(yīng)用構(gòu)建優(yōu)質(zhì)土壤耕層，頭水適當(dāng)晚澆與蹲苗、噴灑生長(zhǎng)調(diào)節(jié)劑、科學(xué)施肥和防治病蟲(chóng)害為核心技術(shù)的綜合調(diào)控栽培措施；構(gòu)建高質(zhì)量健康群體，延緩玉米后期莖稈衰老速率，防止后期莖稈干物質(zhì)分解及水分下降過(guò)快；提高莖稈抗莖腐病能力，改善生育后期莖稈抗倒伏能力。

4.3.1 構(gòu)建優(yōu)質(zhì)土壤耕層 深厚的耕層有利于玉米根系下扎，提高根系生物量和固著力；還可以提高根系活力，有利于水分養(yǎng)分吸收，促進(jìn)地上部莖稈干物質(zhì)積累和機(jī)械強(qiáng)度形成，能夠有效地容納更大的群體[64]。我國(guó)玉米田耕層普遍較淺，全國(guó)平均僅為18.5 cm，遠(yuǎn)低于美國(guó)35 cm左右的耕層，植株易發(fā)生根倒[65]。高密度條件下采用深耕和耕層構(gòu)建技術(shù)，可促進(jìn)玉米根系縱向生長(zhǎng)，提高植株根系生物量和根系活力，增強(qiáng)根系固著能力和養(yǎng)分吸收，防止后期莖稈衰老過(guò)快以及抗病、抗倒能力的過(guò)快下降。

4.3.2 精準(zhǔn)水肥調(diào)控 有灌溉條件的地區(qū)，頭水適當(dāng)晚澆，通過(guò)蹲苗，可以促進(jìn)根系下扎、縮短基部莖節(jié)，增強(qiáng)玉米抗倒性能。生育前期氮肥施用過(guò)多會(huì)促進(jìn)玉米基部節(jié)間快速生長(zhǎng)，導(dǎo)致基部節(jié)間長(zhǎng)度增加[33, 66]；同時(shí)不利于玉米莖稈中纖維素的合成和積累[67]。鉀肥可以促進(jìn)莖稈中結(jié)構(gòu)性碳水化合物積累，單位面積維管束增加，提高莖稈穿刺強(qiáng)度[32, 68-69]；另外，追施鉀肥可以穩(wěn)定細(xì)胞結(jié)構(gòu)，防止細(xì)胞間隙的擴(kuò)大，加固細(xì)胞壁，降低病原菌侵入的機(jī)率[70]。水鉀互作的抗倒伏效果更好[71]，尤其是在滴灌條件下更為明顯[72]。因此，在拔節(jié)期追施鉀肥，大喇叭口期追施氮肥，可以通過(guò)精準(zhǔn)施肥來(lái)控制穗下節(jié)間伸長(zhǎng)，提高莖稈中結(jié)構(gòu)性化學(xué)組分合成和外皮組織形成。

4.3.3 適時(shí)化學(xué)調(diào)控 植物生長(zhǎng)調(diào)節(jié)劑可以緩解由于施用氮肥而引起的莖稈快速生長(zhǎng)現(xiàn)象， 6—8展葉時(shí)噴施乙烯利可以顯著降低株高，提高玉米抗倒伏能力和產(chǎn)量[34-35]。Xu等[36]認(rèn)為在夏玉米7展葉時(shí)噴施EDAH可以提高莖稈的維管束數(shù)目，增強(qiáng)莖稈機(jī)械強(qiáng)度。近年來(lái)，我國(guó)農(nóng)資市場(chǎng)上涌現(xiàn)出“噸田寶”、“羥基乙烯利”、“玉黃金”等一批玉米化控制劑，在密植栽培條件下能有效控制下部節(jié)間伸長(zhǎng)，降低穗位高和重心高度，促進(jìn)節(jié)間干物質(zhì)積累和力學(xué)強(qiáng)度形成，具有較好的抗倒效果。

4.4 因地制宜制定綜合應(yīng)對(duì)措施

玉米種植區(qū)生態(tài)環(huán)境會(huì)影響莖稈發(fā)育階段的質(zhì)量形成[6, 25]，對(duì)生育后期莖稈活性變化、物質(zhì)分解和病蟲(chóng)害發(fā)生也會(huì)造成一定影響[73]，是影響后期倒伏發(fā)生的重要因素之一?；诮隁夂蛱攸c(diǎn)，可以分析我國(guó)不同區(qū)域玉米倒伏發(fā)生的時(shí)期、程度和頻率，制作倒伏風(fēng)險(xiǎn)分布圖，為適合粒收抗倒品種的鑒選確定聯(lián)合測(cè)試網(wǎng)點(diǎn)。在不同玉米產(chǎn)區(qū)，以生態(tài)區(qū)氣候條件為基礎(chǔ)，建立環(huán)境條件（風(fēng)、雨、光照等）、玉米種植密度和抗倒伏指標(biāo)（形態(tài)和生理指標(biāo)）之間的定量化關(guān)系，篩選推薦適合機(jī)械粒收的品種，確立合理的種植密度及適宜的收獲時(shí)期，以降低生育后期倒伏風(fēng)險(xiǎn)。

綜上，玉米生育后期植株衰老使莖稈質(zhì)量下降和莖腐病發(fā)生，提高了倒伏風(fēng)險(xiǎn)?；跈C(jī)械粒收技術(shù)需求的增密種植和田間站稈籽粒脫水加劇和延長(zhǎng)了莖稈衰老進(jìn)程，使莖稈質(zhì)量大幅下降，倒伏問(wèn)題更為突出。今后，應(yīng)從理論基礎(chǔ)、品種選育和栽培措施的應(yīng)用方面研究玉米生育后期的倒伏問(wèn)題，推進(jìn)玉米密植高產(chǎn)和機(jī)械粒收技術(shù)的健康發(fā)展。

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（責(zé)任編輯 楊鑫浩）

Research Progress of Maize Lodging During Late Stage

Xue Jun1, Wang KeRu1, Xie RuiZhi1, Gou Ling2, Zhang WangFeng2, Ming Bo1, Hou Peng1, Li ShaoKun2

(1Institute of Crop Science, Chinese Academy of Agricultural Sciences/Key Laboratory of Crop Physiology and Ecology, Ministry of Agriculture, Beijing 100081;2College of Agronomy, Shihezi University/Key Laboratory of Oasis Eco-agriculture, Xinjiang Production and Construction Corps, Shihezi 832000, Xinjiang)

Lodging is a common problem during maize production. Maize harvested at physiological maturity stage in traditional maize production. Previous researches about maize lodging also focused on stalk development process and some stage before the physiological maturation. There was less lodging research after physiological maturity. Mechanical grain harvest usually was carried out two to four weeks after the physiological maturity. Lodging made mechanical grain harvest become difficulty and increased harvest costs, and it also increased grain losses and decreased the grain quality. Maize lodging was a limiting factor in application of mechanical grain harvest technology. This paper reviewed the physiological changes in the maize senescence process and the influences factors on maize lodging, and proposed the measures and suggestions about improving maize lodging resistance during mid and late stage. Analysis showed that, naturalsenescence of maize from physiological maturity to harvest decreased activity of leaves, stalk and root, and made all of stalk moisture, water-soluble carbohydrate content, hemicellulose content and total structural carbohydrate content decline. These resulted in cell wall thinning, cell gap widening, and stalk strength and disease resistance decrease. The enzymatic activity of PAL, POD and PPO was low, which made the disease resistance decline. The stalk rot pathogen produced cell wall degrading enzymes to decompose cellulose and collapse the cells in stalk. The fungal hyphae flew through the plasma membrane and entered into epidermis cell, cortex and vascular bundle tissue. The stalk rot then increased the speed of stalk dehydration and drying shrinkage, and degraded the pith tissue. Maize stalk became hollow, softening and rot. This decreased stalk quality. Higher grain and full mechanization technologies required high population and delayed harvest to grain dehydration in the field. These accelerated and extension the aging process of maize, further decreased the stalk quality and disease resistance, and increased the lodging risk of maize after physiological maturity. In order to resolve the lodging problem and to accelerate development and promotion of maize mechanical grain harvest technology in China, we suggested that: (1) theoretical research of maize lodging during late stage should be strengthened; (2) germplasm creation should be strengthened to breed new maize cultivars with early-maturity, density-tolerant, high rate of grain dehydration, and strong stress resistance; (3) common methods should be developed to obtain high-quality maize populations and reduce lodging during late stage including constructing a high-quality plow layer, suitable cultivars for grain mechanical harvest, rational close planting, scientific irrigation and fertilization, application of plant growth regulators, and insect-disease prevention; (4) integration countermeasures should also be established according to ecological conditions in different maize regions.

maize; stalk senescence; lodging; mechanical grain harvest; stalk rot

10.3864/j.issn.0578-1752.2018.10.004

2017-11-07；

2018-01-17

國(guó)家重點(diǎn)研發(fā)計(jì)劃（2016YFD0300110）、國(guó)家自然科學(xué)基金（31371575)、中國(guó)農(nóng)業(yè)科學(xué)院農(nóng)業(yè)科技創(chuàng)新工程、國(guó)家玉米產(chǎn)業(yè)技術(shù)體系項(xiàng)目（CARS-02-25）

薛軍，E-mail：xuejun5519@126.com。通信作者李少昆，Tel：010-82108891；E-mail：lishaokun@caas.cn