Inoculation of Eucalyptus urophylla with spores of Scleroderma in a nursery in south China:: Comparison of field soil and potting

Non-pasteurized soil or soil-based rooting media are being used to raise eucalypts in nurseries in south China. It is unclear whether these practices are optimal for the growth of eucalypt plants or the development of ectomycorrhizal associations. Therefore, there is a need to optimize nursery practices to meet the demand for high quality seedlings and clonal lines of Eucalyptus urophylla and hybrids, for outplanting in the region. Inoculation with spores of ectomycorrhizal fungi is accepted as desirable due to potential yield benefits in the field. Previous studies have shown that spores of some collections of Scleroderma are vigorous colonizers on E. urophylla seedlings. These could be used in inoculation programs in China if nursery conditions were suitable for ectomycorrhizal development and the fungi persisted in the field. Therefore, effects of rooting medium and inoculation with Scleroderma on the growth of E. urophylla were examined in a nursery in south China. A complete randomized block design consisting of five rooting media and eight fungal inoculation (six fungi in non-sterile media, two uninoculated controls either in non-sterile or sterile media) was used. Four types of soil taken from eucalypt plantations in south China were compared to a potting mix with vermiculite, peat and sand. Spores of six Scleroderma taxa were taken from basidiomes collected from under eucalypt plantations in Western Australia and south China. Soil substrates significantly affected the growth of seedlings with large variation in both height and biomass. Seedlings grown in the potting mix were larger (90-220% in shoot height, and 110-420% in total dry weight) than those in soil. Inoculation with spores of Scleroderma to non-sterile soil generally promoted the growth of seedlings and their nutrient acquisition. Inoculation increased the growth of seedlings by 19-55% in shoot height and 25-41% in total biomass, compared to uninoculated plants in each soil. Although the ability to form ectomycorrhizas varied considerably between spore collections, most Scleroderma taxa vigorously colonized roots. However, the potting media significantly influenced the extent of colonization by Scleroderma. Some 58% of short roots were infected by Scleroderma in the potting mix, whilst only 12-18% of short roots were ectomycorrhizal in the granitic loam and the red clay. The three Australian collections generally colonized a larger proportion of short roots of plants than those from China origin, especially when plants were grown in the potting mix or lateritic loam. In conclusion, the potting mix was better than soil in promoting growth of plants and mycorrhization from Scleroderma spores, and five collections of Scleroderma were able to form ectomycorrhizas in non-pasteurized field soil under nursery conditions. The inoculant Scleroderma were able to out-compete indigenous mycorrhizal fungi in the rooting media. Soils collected from the field were not optimal for the growth of plants or ectomycorrhizal development under nursery conditions. These results challenge the current practices in eucalypt nurseries and following nursery practices are recommended to be modified: (i) due to the low diversity of compatible fungal symbionts in field soil, inoculation with tested ectomycorrhizal fungi, such as Scleroderma in this study, is recommended for eucalypts prior to outplanting. (ii) Low cost potting mix of suitable porosity and organic matter content should be explored as alternatives to soil. (iii) The lateritic loam may be used as rooting medium in eucalypt nurseries whilst other three types of field soil are not recommended. (iv) Rooting media should not necessarily be pasteurized when raising mycorrhizal plants in eucalypt nurseries in south China. (c) 2005 Elsevier B.V. All rights reserved.