广西赭霉X22对苦瓜的促生防病作用及对叶际细菌群落的影响

The effects Ochroconis guangxiensis X22 on preventing powdery mildew, promoting growth, and regulating phyllosphere bacterial community of Momordica charantia

摘要:

【背景】 深色有隔内生真菌(dark septate endophyte, DSE)是植物共生真菌的典型代表之一，具有增强植物抗病性和促进植物生长等潜能，此外，DSE生态分布广泛、可分离纯培养及定殖无寄主特异性的特点为其在农业生产、环境保护及修复等方面带来广阔的应用前景。【目的】 以7株菌株为研究对象，从中筛选对苦瓜白粉病有良好生防效果的菌株，探究其对叶际细菌群落结构和多样性的影响。【方法】 采用浸种+淋土+灌根接种法通过盆栽试验对7株DSE菌株防治苦瓜白粉病的效果进行评价，通过浸种法测定优良菌株对苦瓜种子萌发和生长的影响，并基于16S rRNA基因高通量测序结果，分析苦瓜接种菌株X22后在白粉病发生初期、中期和后期叶际细菌群落结构特征。【结果】 筛选获得一株优良生防菌株——广西赭霉(Ochroconis guangxiensis) X22，其对苦瓜白粉病的室内防治效果达56.58%，接种X22 (O+)的苦瓜种子发芽率显著提高，苦瓜出苗相对较整齐，苦瓜苗的叶片数、茎径和叶色值(soil and plant analyzer development, SPAD)分别较对照(O-)提高3.18%、6.08%和7.88%，株高比O-提高了22.59%，差异达显著水平。相较于O-，O+的叶际细菌α多样性在白粉病发生初期、中期和后期均有所提高，丰度则表现为增-减-增。在白粉病发生的各个阶段，O+与O-这2个处理在门水平上优势菌门及其丰度差异不显著；在属水平上，初期和中期2个处理优势菌属及其相对丰度存在差异，并且O+特异富集了参与氮循环的铁氧化菌属(Sideroxydans)和缺氧反硝化菌属(Natronincola)及具抑菌作用的放线菌糖单孢菌属(Saccharomonospora)等有益菌。【结论】 DSE菌株X22对苦瓜白粉病具有较好的防治效果，同时可促进苦瓜种子萌发和植株生长，可能是通过调节叶际细菌群落结构维持其多样性和稳定性，并招募具抑菌活性和固氮能力的有益菌抑制病原菌，为宿主提供氮源促进宿主生长，从而提高宿主抗病性。菌株X22是一株很有开发应用潜力的生防菌株。

关键词:深色有隔内生真菌;苦瓜白粉病;促生;高通量测序;叶际细菌;群落结构

Abstract:

[Background] Dark septate endophytes (DSEs) are representatives of endophytic fungi capable of enhancing the disease resistance and promoting the growth of plants. With wide distribution, culturability, and non-host specificity, DSEs demonstrate broad application prospects in agricultural production as well as environmental protection and restoration. [Objective] To screen the DSE strain(s) capable of controlling powdery mildew in bitter gourd (Momordica charantia) out of seven strains and investigate the effects of the strain(s) screened out on the phyllosphere bacterial community of M. charantia plants. [Methods] We carried out pot experiments with the seed soaking+soil spraying+root irrigation methods to study the effects of seven DSE strains on powdery mildew of M. charantia. The effects of the strain screened out on the seed germination and plant growth of M. charantia were studied by the seed soaking method. The 16S rRNA gene high-throughput sequencing was employed to reveal the structure of phyllosphere bacterial community in the early, middle, and late stages of powdery mildew in M. charantia inoculated with the strain screened out. [Results] The strain X22 (Ochroconis guangxiensis) was screened out as a potential biocontrol agent, with the control efficacy of 56.58% on powdery mildew of M. charantia. Compared with the non-inoculated control (O-), inoculation with X22 (O+) increased the seed germination rate and led to uniform seedlings. The inoculation increased the leaf number, stem diameter, SPAD, and plant height by 3.18%, 6.08%, 7.88%, and 22.59% (P<0.05), respectively. Compared with O-, O+ showcased increased alpha diversity of phyllosphere bacteria in the early, middle, and late stages of powdery mildew, while the abundance of phyllosphere bacteria in the O+ group presented an increase-decrease-increase trend. In all the stages of powdery mildew, neither the dominant phyla nor their relative abundance there were no significant differences between O- and O+ groups. In the early and middle stages of powdery mildew, the dominant genera and their relative abundance showed significant differences between the two groups. Specifically, beneficial bacterial genera such as Sideroxydans, Saccharomonospora, and Natronincola involved in the nitrogen cycle or with antimicrobial activity were enriched in the O+ group. [Conclusion] The DSE strain X22 exhibited good biocontrol effect on powdery mildew and promoted the seed germination and plant growth of M. charantia. It may regulate the community structure to maintain the diversity and stability of phyllosphere bacteria. Meanwhile, this strain can recruit beneficial bacteria with antimicrobial activity and nitrogen-fixing ability to inhibit pathogens and provide nitrogen sources for hosts to promote host growth, thereby improving host disease resistance. The strain X22 is a biocontrol agent with great potential for development and application.

Key words:dark septate endophyte;powdery mildew of Momordica charantia;growth-promoting;high-throughput sequencing;phyllosphere bacteria;community structure