A low-cost method of mycorrhizal inoculation improves growth of Acacia tortilis seedlings in the nursery

A pot experiment in Kenya examined the effects of mycorrhizal and rhizobial inoculation on the growth and symbiont infection of Acacia tortilis seedli ngs in unsterile soil, in comparison with sterile and unsterile soil contro ls. Three mixed, arbuscular mycorrhizal inocula, originating from A. tortil is, Terminalia brownii, T. spinosa and Prosopis juliflora (produced under n ursery conditions), were used to inoculate the seedlings, which also receiv ed a standard, mixed, rhizobial inoculum. Mycorrhizal infection and plant g rowth were significantly affected by experimental treatment (p<0.001). Some mycorrhizal infection (presumably with indigenous soil-borne inoculum) occ urred in the unsterile soil control, but not in the sterile soil control, i ndicating that transfer of inoculum between pots in the experiment did not occur. Mycorrhizal formation was significantly more extensive in inoculated plants, which also had better shoot and root growth. 24 weeks after inocul ation, plants which had received inoculum of A. tortilis origin were 105 mm tall and their roots were 56% mycorrhizal, whereas the controls most repre sentative of normal nursery treatment were only 77 mm tall and 29% mycorrhi zal. Nodulation was erratic and poor in all treatments. The results suggest that mycorrhizal inoculation can improve both mycorrhizal infection and gr owth of tree seedlings in unsterile nursery soil. The methods of culture an d inoculation described here could easily be adopted by nurseries at Little cost. (C) 1999 Published by Elsevier Science B.V. All rights reserved.