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Mycorrhizal Symbiosis for Enhancement of Nursery Grown Tectona grandis L. and Gmelina arborea Roxb
Abstract:
Arbuscular mycorrhizal (AM) fungi are soil fungi which form mutualistic associations with plant roots which often promote plant growth through increased mineral nutrient acquisitions from the highly weathered tropical soils. In the field, seedlings infected with mycorrhiza often survive and grow better than the control. This study aimed to evaluate the effectivity of AM in the growth of two forest plantation species, namely: Tectonas grandis and Gmelina arborea seedlings. The effectivity of these AM inocula was assessed using both quantitative and qualitative analyses.
This study used two types of AM designated as MM (arbuscular mycorrhiza from Malaysia) and IM (arbuscular mycorrhiza from Indonesia). The effectivity of these inocula was initially evaluated based on standard protocols, spore count, most probable number (MPN) bioassay, and growth performance of T. grandis and G. arborea. The seedlings were grown in a controlled environment in the glasshouse for 21 weeks. Growth measurements were taken every three weeks. The nursery experiment adopted a randomized complete factorial design of three media and four inocula treatments with six replications. In addition, isozyme analysis and root colonization for host preference were conducted to support this study.
Laboratory assessment of inocula indicated lower spore number (24 spores per 10 g inoculum) and MPN bioassay (87.5 propagules per g inoculum) in MM. Inoculum MM comprised three spore types from genera Glomus, Gigaspora, and Scuttellospora. On the other hand, IM recorded a higher spore number (55 spores per 10 g inoculum) and MPN bioassay (325 propagules per g inoculum). Even though IM comprised three spore types as in MM, only two were similar, the exception was Acaulospora.
Generally, the growth responses of the seedlings were affected significantly by media, AM inocula, and their interactions. It was found that both inocula (MM and IM) responded similarly (no significant difference) but when compared with their controls, they showed significant difference at (p < .05) in all growth parameters measured. Morphological observations also revealed that the AM treated seedlings were more vigorous than their controls. Inoculum IM showed significantly higher mean values of photosynthetic rate (4.96 and 4.72 mol/m2/s) and chlorophyll content (358.33 and 689.44 SPAD porometer) for T. grandis and G. arborea, respectively than MM. Zymogram patterns revealed by isozyme analysis of alkaline phosphatase (ALP) indicated the presence of IM spores in the roots of these seedlings. Root colonization of host preferences also indicated that MM or IM has same host preference. From this study, it can be concluded that AM fungi have potentials to improve the growth and physiological characteristics of these seedlings.