减氮条件下青枯病破坏连作芝麻根际土壤细菌群落结构和功能的机制

At present, there are obvious obstacles to the continuous sesame cropping and serious bacterial wilt of sesame was frequently observed. Meanwhile, it was found that less nitrogen application rate could alleviate the sesame diseases caused by continuous cropping. By using high-throughput sequencing and metagenomics technology, the nitrogen fertilizer reduction experiment was conducted to figure out the yield, root characteristics and disease index under continuous 2-year sesame cropping conditions. Furthermore, it could identify the difference of rhizosphere soil sample between the healthy and diseased plants, and find out the key environmental factors that affect the structure of the bacterial community. To elucidate the temporal succession of rhizosphere soil bacterial community structure and analysis the disrupting mechanism of the bacterial community structure by bacterial wilt and its related functional genes enrichment processes under 2-year sesame cropping conditions, and to investigate the response characteristics of soil bacterial community structure in sesame rhizosphere soil from healthy and diseased soil could provide theoretical guidance for future research on technology of alleviating continuous sesame cropping obstacle.

针对目前芝麻连作障碍明显，芝麻青枯病发生严重，同时在生产中也发现氮肥少施对连作芝麻病害有一定的减缓作用。采用高通量测序技术和宏基因组技术，研究氮肥减量施用对连作2年芝麻的产量和根系特征以及青枯病病情指数的影响规律，明确正常株和患病株的根际土壤细菌群落多样性和结构组成的差异特征，找出影响细菌群落结构的关键环境因子。阐明连作芝麻根际土壤细菌群落结构的时间演替特征，分析青枯病破坏连作2年芝麻根部相关细菌群落结构组成及其相关功能基因的富集过程的机制。探索连作芝麻根际土壤细菌群落结构对健康株和患病株土壤的响应特征。为今后开展芝麻连作障碍缓解技术研究提供理论指导。

针对生产中发现少施氮肥能够降低连作芝麻青枯病病情指数和产量损失的现象。设置了多项减氮条件下青枯病破坏连作芝麻根际土壤细菌群落结构和功能的试验。结果显示，105kg.hm-2基础上氮肥用量减少25%（RSN3）的芝麻产量较不减施未出现明显下降。减施75%的放线菌门相对丰度较RSN3的显著增加了39.70%，而厚壁菌门显著下降了30.60%；来自健康株根际土壤的酸杆菌门、蓝藻门、硝化螺旋菌门相对丰度较来自患病株的显著高出32.42%、155.26%、38.54%，而厚壁菌门较患病株的显著下降了47.47%；105kg.hm-2基础上减氮25%，发病程度处理间（健康株H0；中等D5；严重D9）多样性指标都无显著差异，但取样时期处理间（初花后0天，F0；F11；F21；F32；F48）都有显著差异。D5处理的变形菌门和放线菌门相对丰度较H0的显著增加10.60%和14.23%。D9处理的变形菌门相对丰度较H0的显著增加了11.55%；F32和F48的变形菌门和芽单胞菌门的相对丰度显著高于其他处理。取样时期对细菌群落结构和功能的影响分成初花期至终花期，终花期至成熟期2个时间段。三个处理间（健康株WH；5级WD5；9级WD9）的基因数目无显著差异，总体表现为WD9>WD5>WH；三个处理共有基因数量为252个，特有基因分别为1个（AAC3-IIIb）、6个（AAC6-Iaj；lnuG；AAC3-IIa；blt；OXA-243；msbA）、1个（cfrC）。WH与WD9中Energy metabolism、Nucleotide metabolism、Amino acid metabolism有较大差异。氮代谢通路比较中共有的酶类主要有NirK和NirS；WH独有的酶类主要有NarB，Hao，NitDKH，AnoCAB；WD9独有酶类有3.5.1.49。前茬不同生长状态芝麻根际土壤对后茬芝麻根体积、根干重、单株产量、细菌群落α多样性、青枯病病情指数都有显著影响。来自前茬健康株土壤的正常株土壤的变形菌门较其他处理有显著增加，而放线菌门显著减少； Metabolism of other amino acids，Signal transduction，Cell motility是影响芝麻健康生长的关键功能。本研究结果对芝麻连作障碍的缓解具有重要意义。