Effect of foliage inoculation with sporangiospores of VAM fungus produced in axenic culture on growth of pineapple plantlets during the in vitro and ex Vitro acclimatization stages. Proc. 11th Cong. Egypt. Phytopathol. Soc., November 2007, Giza, Egypt, pp. 379-392.
|Authors:||El-Fiki, A.I.I.; N.A.A. Haggagi and K.E. Eid|
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Pineapple (Ananas comosus cv. Smoth cauun) plantlets were inoculated pre culture by dipping their shoot tips for few seconds in different concentrations of spore (sporangiospore) suspension of the in vitro grown VAM-fungus (onion isolate). Some growth criteria of pineapple plantlets as affected by these treatments were measured twice (after the in vitro and ex vitro acclimatization periods). All inoculation treatments significantly improved plantlet growth (plantlet height, greening degree, number of leaves and number of roots/plantlet as well as root length) compared with the untreated control ones. The lowest spore concentration (0.85 x 106 spores/ml) gave the best results in this respect. The VAM-spores germinate well on the leaf surface and their germ tubes grew, ramify and colonize the stomatal openings and its surrounding cells. All structures characterized the VAM-infection i.e. inter- and intra-cellular aseptate hyphae, vesicles, arbuscules and chlamydospores were extensively seen in leaves, stem and roots of the treated pineapple plantlets. Some of these structures particularly vesicles were seen also in roots of untreated (control) pineapple plantlets. These results concluded the followings. 1) The native “inhabitant” VAM fungi (as the case in control plantlets) had no any visible improvement in plant growth. 2) The external “invader” VAM infection could be induced by air-borne inocula (sporangiospores). 3)The VAM infection occurred systemically in all plant portions. Accordingly, the global term “Vesicular arbuscular mycorrhizal (VAM) fungi” needs to re-revised. The term “Vesicular arbuscular systemic endophytic fungi might be more suitable. The usefulness of foliar application of the in vitro VAM inocula (sporangiospores) for improving growth of pineapple plants during acclimatization was recorded for the first time during this study. Thus, the gateway was broadly opened to applying these beneficial fungi under opened field conditions. Key words: vesicular arbuscular mycorrhizae, VAM, inoculum, sporangiospores, pineapple, Ananas comosus, foliar inoculation, systemic colonization.