Ohtomo Ryo, Kobae Yoshihiro, Morimoto Sho, Oka Norikuni
Hokkaido Agricultural Research Center, NARO.
Microbes Environ. 2018 Mar 29;33(1):34-39. doi: 10.1264/jsme2.ME17098. Epub 2018 Mar 6.
The effective use of arbuscular mycorrhizal (AM) fungal function to promote host plant phosphate uptake in agricultural practice requires the accurate quantitative evaluation of AM fungal infection potential in field soil or AM fungal inoculation material. The number of infection units (IUs), intraradical fungal structures derived from single root entries formed after a short cultivation period, may reflect the number of propagules in soil when pot soil is completely permeated by the host root. However, the original IU method, in which all AM propagules in a pot are counted, requires the fine tuning of plant growing conditions and is considered to be laborious. The objective of the present study was to test whether IU density, not the total count of IU, but the number of IUs per unit root length, reflects the density of AM fungal propagules in soil. IU density assessed after 12 d of host plant cultivation and 3,3'-diaminobenzidine (DAB) staining showed a stronger linear correlation with propagule density than the mean infection percentage (MIP). In addition, IU density was affected less by the host plant species than MIP. We suggest that IU density provides a more rapid and reliable quantitation of the propagule density of AM fungi than MIP or the original IU method. Thus, IU density may be a more robust index of AM fungal infection potential for research and practical applications.
在农业实践中，有效利用丛枝菌根（AM）真菌功能来促进宿主植物对磷的吸收，需要准确量化田间土壤或AM真菌接种材料中AM真菌的感染潜力。感染单位（IU）的数量是指在短时间培养后由单个根系侵入形成的根内真菌结构，当盆栽土壤被宿主根系完全渗透时，它可能反映土壤中繁殖体的数量。然而，最初的IU方法需要对植物生长条件进行微调，且需要对盆栽中的所有AM繁殖体进行计数，被认为比较繁琐。本研究的目的是检验IU密度（即单位根长度的IU数量，而非IU总数）是否能反映土壤中AM真菌繁殖体的密度。宿主植物培养12天后评估的IU密度以及3,3'-二氨基联苯胺（DAB）染色显示，与平均感染率（MIP）相比，IU密度与繁殖体密度的线性相关性更强。此外，IU密度受宿主植物种类的影响比MIP小。我们认为，与MIP或最初的IU方法相比，IU密度能更快速、可靠地量化AM真菌的繁殖体密度。因此，IU密度可能是研究和实际应用中AM真菌感染潜力更可靠的指标。
