Methods for Applying Inoculum

Most commercially available AM bulk inoculum is a mixture of spores, colonized roots, hyphae, and the substrate on which pot cultures were grown. For EM fungi, many inoculation programs have successfully used the EM vegetative mycelium. The production of mycelial inoculum for large-scale inoculation programs is often costly and pure culture isolates can be difficult to maintain (Marx and Kenney 1982). In contrast, EM sporocarps contain a significant amount of spores that can be collected from the fruiting populations and easily dried and stored until application. Spores from EM fruiting bodies of Pisolithus, Scleroderma, and Rhizopogon are most frequently used as inoculum. Spores of Laccaria, Descolea, Scleroderma and Pisolithus spp. have recently been proposed as candidates for nursery inoculation programs for eucalypti (Lu et al. 1998) and Rhizopogon spp. are commonly used to inoculate Doulgas-fir seedlings in commercial nurseries (Castellano 1994).

The amount, timing, and method of inoculation are important factors in properly managing the establishment of mycorrhizae. Little is known about appropriate application rates. Estimates of 1-2kg of bulk soil inoculum (5000-10,000 propagules) have been used for AM inoculations (Lovato et al. 1995) and spore suspensions at densities of 106-107 spores per ml have been used for EM inoculations (Lu et al. 1998). The earlier plants are inoculated with fungi, the greater the benefits are to those plants. Inoculation is typically applied in either by broadcasting at the soil surface or by banding inoculum at the root zone. Broadcasting requires more inoculum whereas banding concentrates inoculum near the area of developing roots. Transplanting mycorrhizal seedlings can also be used to inoculate other plant roots. Fungal hyphae expand into open habitats and along roots, slowly spreading the association to adjacent plants (Warner and Mosse 1980).

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