Table_4_Seasonal Variation and Crop Sequences Shape the Structure of Bacterial Communities in Cysts of Soybean Cyst Nematode.XLSX

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is the number 1 pathogen of the important economic crop soybean. Bacteria represent potential biocontrol agents of the SCN, but few studies have characterized the dynamics of bacterial communities associated with cysts under different crop rotation sequences. The bacterial communities in SCN cysts in a long-term soybean–corn crop rotation experiment were investigated over 2 years. The crop sequences included long-term soybean monoculture (Ss), years 1–5 of soybean following 5 years corn (S1–S5), years 1 and 2 of corn following 5 years soybean (C1 and C2), and soybean–corn annual rotation (Sa and Ca). The bacterial 16S rRNA V4 region was amplified from DNA isolated from SCN cysts collected in spring at planting, midseason (2 months later), and fall at harvest and sequenced on the Illumina MiSeq platform. The SCN cyst microbiome was dominated by Proteobacteria followed by Actinobacteria, Bacteroidetes, and Verrucomicrobia. The bacterial community composition was influenced by both crop sequence and season. Although differences by crop sequence were not significant in the spring of each year, bacterial communities in cysts from annual rotation (Sa and Ca) or crop sequences of early years of monoculture following a 5-year rotation of the alternate crop (S1 and C1) became rapidly differentiated by crop over a single growing season. In the fall, genera of cyst bacteria associated with soybean crop sequences included Rhizobacter, Leptothrix, Cytophaga, Chitinophaga, Niastella, Streptomyces, and Halangium. The discovery of diverse bacterial taxa in SCN cysts and their dynamics across crop rotation sequences provides invaluable information for future development of biological control of the SCN.

大豆孢囊线虫（Soybean cyst nematode, SCN，学名Heterodera glycines Ichinohe）是重要经济作物大豆的头号病原物。细菌是一类具有潜力的SCN生防因子，但目前鲜有研究阐明不同作物轮作序列下，孢囊相关细菌群落的动态变化规律。本研究针对一项长期大豆-玉米轮作试验中的SCN孢囊内细菌群落，开展了为期2年的调查。试验设置的轮作序列包括：长期大豆连作（Ss）、5年玉米种植后接续1-5年大豆种植（S1–S5）、5年大豆种植后接续1-2年玉米种植（C1和C2），以及大豆-玉米年度轮作（Sa和Ca）。研究人员从春季播种期、生育中期（播种后2个月）与收获期秋季采集的SCN孢囊中提取DNA，扩增细菌16S rRNA V4高变区，并基于Illumina MiSeq平台完成测序。结果显示，SCN孢囊微生物组以变形菌门（Proteobacteria）为优势类群，其次为放线菌门（Actinobacteria）、拟杆菌门（Bacteroidetes）与疣微菌门（Verrucomicrobia）。细菌群落组成同时受轮作序列与季节的显著影响。尽管每年春季的样本中，不同轮作序列间的群落差异并不显著，但年度轮作（Sa和Ca）的孢囊细菌群落，或是经过5年非寄主作物轮作后初期连作的序列（S1和C1），均可在单个生长季内随作物类型快速出现群落分化。秋季时，与大豆轮作序列相关的孢囊细菌属主要包括根杆菌属（Rhizobacter）、纤发菌属（Leptothrix）、噬纤维菌属（Cytophaga）、几丁质杆菌属（Chitinophaga）、尼斯特拉菌属（Niastella）、链霉菌属（Streptomyces）与海兰杆菌属（Halangium）。本研究揭示了SCN孢囊内多样的细菌类群及其随作物轮作序列的动态变化特征，可为未来开发SCN生物防治策略提供极具价值的参考信息。