Abstract
The effect of citrus juice pomace extracts on in vitro hyphal growth of vesicular-arbuscular mycorrhizal (VAM) fungi and the mycorrhizal formation on trifoliate orange (Poncirus trifoliata Raf.) seedlings and Citrus iyo Tanaka trees was investigated. One hundred μl [equivalent to 6.5 g dry weight (DW) of satsuma mandarin (Citrus unshiu Marc.) and 4.3 gDW of Citrus hassaku Tanaka] of the 25% MeOH eluates of citrus juice pomace extracts significantly increased in vitro hyphal growth of Gigaspora ramisporophora Spain, but a 100% MeOH eluates inhibited it. In a plot where the solution consisting of 25% MeOH eluates of satsuma mandarin juice pomace extracts (equivalent to 10 gDW) and liquid fertilizers was applied to the soil inoculated with the spores of Gigaspora ramisporophora, the percentage of VAM infection in trifoliate orange roots was six times higher than that in the control (water only) after one week. When the above mixed solution was administered to a Citrus iyo orchard via a sprinkler irrigation system, VAM development was markedly stimulated as compared to the untreated plots (liquid fertilizer only) and the control (solid fertilizer only). These results show that 25% MeOH eluates of citrus juice pomace extracts contain stimulatory substances for VAM fungi. Furthermore, the application of the 25% MeOH eluates to the soil is very effective in stimulating VAM development.
