连作花魔芋软腐病株与健株根域丛枝菌根真菌群落多样性

Diversity of arbuscular mycorrhizal fungi in the root zone of Amorphophallus konjac with and without soft rot under continuous cropping

摘要:

【目的】解析不同连作年限花魔芋软腐病株、健株根域的丛枝菌根真菌(arbuscular mycorrhizal fungi，AMF)群落多样性。【方法】使用AMF 18S SSU rRNA基因特异引物AMV4.5NF/AMDGR对正茬及连作2年和3年的软腐病株、健株魔芋根系和根际土壤DNA扩增建库，通过高通量测序和生物信息学分析探究魔芋软腐病与其根域AMF群落多样性的关系。【结果】魔芋根系具有明显的AMF菌丝、泡囊和丛枝等结构。在相同连作年限条件下，健株根系AMF总侵染率、侵染强度和孢子密度均显著高于病株(P<0.05)；在不同连作年限条件下，病株根系AMF总侵染率和侵染强度随连作年限延长而降低。从所有样品中共鉴定到9属53种AMF，其中有49个已知种和4个新种。球囊霉属(Glomus)和类球囊霉属(Claroideoglomus)是AMF群落的优势属，其AMF种分别占总AMF种数的41.5%和26.4%；丰度最高的Paraglomus sp.VTX00308是所有样品的共有种。连作、软腐病及二者的交互作用显著影响根系AMF群落的Shannon指数和Simpson指数及根际土壤AMF的Chao1指数(P<0.05)。通过丰度差异分析发现6个在连作软腐病发生后丰度差异显著的AMF种(P<0.05)；NMDS分析表明，不同连作年限的魔芋软腐病株与健株之间的根域AMF菌种组成、相对丰度和群落结构存在差异。相关性分析表明，软腐病发病率和病情指数与魔芋根系和根际土壤AMF的Shannon指数、根系AMF的Chao1和Simpson指数以及AMF总侵染率、侵染强度和孢子密度极显著负相关(P<0.01)。【结论】比对健株，连作魔芋软腐病株根际土壤AMF孢子密度以及根系AMF侵染率、种数和多样性均降低，其群落结构显著改变。

Abstract:

[Objective] To explore the diversity of arbuscular mycorrhizal fungi (AMF) in root zone of Amorphophallus konjac with and without soft rot under different durations of continuous cropping.[Methods] A specific primer pair (AMV4.5NF/AMDGR) targeting the 18S small subunit rRNA gene of AMF was used for PCR amplification of the DNA from the root and rhizosphere soil samples of diseased and healthy A. konjac plants under non-continuous cropping and 2 and 3 years of continuous cropping, respectively, and the DNA library was constructed. Based on high-throughput sequencing and bioinformatics analysis, the relationship between soft rot and AMF diversity in the root zone of A. konjac was investigated. [Results] AMF infection occurred in the roots of A. konjac with specific structures such as hyphae, vesicles, and arbuscules. The total infection rate, infection intensity, and spore density of AMF in healthy plants were significantly higher than those in diseased plants under the same continuous cropping duration (P<0.05). Both the total infection rate and infection intensity of AMF in diseased plants decreased remarkably with the prolongation of continuous cropping. A total of 53 species in 9 genera of AMF (49 known species and 4 novel species) were identified from all samples. Glomus and Paraglomus were the dominant genera of AMF, accounting for 41.5% and 26.4% of the total AMF community, respectively. Among the species identified, Paraglomus sp. VTX00308 showed the highest relative abundance (12.3%) and was shared by all samples. Continuous cropping duration, soft rot, and their interaction significantly affected the Shannon and Simpson indices of AMF in the roots and the Chao1 of AMF in the rhizosphere soil (P<0.05). Six AMF species considerably varied in relative abundance after soft rot occurred under continuous cropping (P<0.05). Difference in AMF species composition, relative abundance, and community structure was revealed between diseased and healthy plants under different continuous cropping durations by non-metric multidimensional scaling. Correlation analysis indicated that the incidence and severity index of soft rot were negatively correlated with the Shannon index (root and rhizosphere soil), Chao1 (root), Simpson index (root), total infection rate, infection intensity, and spore density of AMF in the root zone of A. konjac (P<0.01). [Conclusion] AMF spore density in the rhizosphere soil and AMF infection rate, species number, and community diversity in the roots of A. konjac plants with soft rot all decreased compared with those of the healthy plants, leading to remarkable shifts in the root-zone AMF community structure under continuous cropping. Our results suggest that soft rot occurrence during continuous cropping may reshape the AMF community in the root zone of A. konjac through altering the species composition, relative abundance, and diversity of AMF in both the roots and rhizosphere soil.