滩涂盐碱地根际镰孢菌种类、非生物胁迫抗性及致病性

Rhizosphere Fusarium species in coastal halophytes and their abiotic tolerance and potential pathogenicity

镰孢菌Fusarium spp.通常引起多种作物病害,但其中某些种类可作为植物内生菌从而提高植物的生长和抗逆性。因此,研究非农田生态系统镰孢菌物种多样性和生态功能具有重要的科学意义。本研究对分离自滩涂盐碱地盐生植物根际的23株镰孢菌进行了种类鉴定、非生物胁迫抗性及毒性评价研究。结果表明:经形态学和多基因联合建树分析(ITS+rpb2+tef1-α),这些菌株属于7个系统发育种,多数菌株属于尖孢镰孢菌F.oxysporum、恶臭镰孢菌F.foetens和藤仓镰孢菌F.fujikuroi。在7种非生物胁迫条件下[H2O2、亚硫酸氢钠甲萘醌(menadione sodium bisulfite,MSB)、KCl、山梨醇(sorbitol)、荧光增白剂(calcofluor white,CFW)、刚果红(congo red)、NaCl]测定菌株抗性,上述3种镰孢菌与Fusarium sp.1表现出相似的抗性能力;Fusarium sp.2和Fusarium sp.3尤其在离子胁迫和渗透胁迫方面表现出较强的适应性;芳香镰孢菌F.ambrosium则对多种胁迫均比较敏感。PCR检测表明大多数菌株含有恩镰孢菌素(enniatin)合成核心基因,约1/3菌株包含伏马菌素(fumonisin)基因,少量菌株含有单端孢霉烯族毒素(trichothecene)基因。只有少量菌株扩增出six2、six9和six13等编码木质部分泌蛋白SIX(secreted in xylem)的基因。接种试验表明,多数菌株对拟南芥和NL895杨树无性系具有不同程度的致病性,只有少量菌株具有明显的促生效应;而所有菌株接种小麦幼苗均未引起病害。研究发现促生和致病菌株在毒素合成基因和six基因数量方面并无明显差异,表明还存在其他致病或促生机制。本研究揭示了盐生植物根系存在较为丰富的镰孢菌种类,而且存在致病或促生等方面的差异。本研究为深入研究营养方式转变的基因组演化特征和植物-镰孢菌的共生互作提供了模型。

Fusarium spp.are notorious,causing devastating diseases of many crops and trees.However,the degree of diversity and ecological significances of Fusarium species in non-agricultural ecosystems is still less known.This paper aims at revealing the diversity of Fusarium species from coastal saline areas,and their traits relevant to abiotic stress and pathogenicity.Abiotic stress includes the stresses induced by H2O2,MSB,KCl,sorbitol,CFW,congo red and NaCl.In total,23 Fusarium strains were isolated from rhizosphere soil of halophytes.A combination of morphology and multi-loci(ITS+rpb2+tef1-α)phylogeny classified the tested strains into seven phylogenetic species.Among them,F.oxysporum,F.foetens,F.fujikuroi and Fusarium sp.1 showed similar patterns of resistant ability to abiotic stresses,while a potential novel group(Fusarium sp.2 and Fusarium sp.3)was more resistant to the majority of stresses.F.ambrosium was more susceptible to the stresses.Most strains harbored the gene for enniatin biosynthesis,and approximately one third of the strains retained genes for fumonisins.Only very few had trichothecenes related genes(tri5 and tri11).Only six2,six9,and six13 coding effectors(secreted in xylem)were amplified from a small fraction of strains.Inoculation experiments demonstrated that most Fusarium strains displayed varied degrees of pathogenicity to Arabidopsis and poplar plants,and few of them significantly improved plant growth.Unexpectedly,all Fusarium strains did not cause symptoms in wheat seedlings.Intriguingly,there was no clear difference between pathogenic and beneficial Fusarium strains with regard to their number of toxin biosynthetic and six genes.Our work provides model for revealing the genomic evolution behind the trophism shift in Fusarium and addressing plant-Fusarium mutualistic interactions.