Isolate-specific rooting responses of Leucothoe fontanesiana cuttings to inoculation with ericoid mycorrhizal fungi

We assessed whether adding ericoid mycorrhizal fungi (EMF) to the rooting substrate during cutting propagation altered rooting and root growth of Leucothoe fontanesiana ‘Rainbow’. Hardwood cuttings, treated or untreated with rooting hormone prior to sticking into rooting substrate, were grown with one of three isolates of EMF as inoculum or with no inoculum (control). Cuttings were placed under mist in a greenhouse, with no bottom heat, and harvested 63, 84 and 109 d after sticking. Cuttings in substrate inoculated with two of the three EMF isolates showed better rooting than in non-inoculated substrate 63 d after sticking. However, by the end of the experiment, there were no differences in rooting between cuttings in the different inoculation treatments. Only cuttings in pots inoculated with one of the EMF isolates had consistently higher root initiation and weight than non-inoculated cuttings at all harvest dates. Root initiation and weight of cuttings in pots inoculated with either of the other two EMF isolates were greater than non-inoculated cuttings only when the cuttings had been treated with rooting hormone. In general, roots on EMF-inoculated cuttings were less branched and longer than roots on non-inoculated cuttings. Root colonisation was positively correlated with root initiation, length and weight 63 d after sticking; while, at later harvest dates, root colonisation was positively correlated only with root weight. The ability of EMF to increase rooting during cutting propagation of easy-to-root species, may decrease root production time. EMF-induced increases in root initiation during cutting propagation appear to be related to specific plant-fungus interactions and to interactions with rooting hormone. Although there were isolate-specific differences in rooting response, EMF-induced changes in root size and anatomy appear to be time-dependent and may influence the function of the new root system relative to water use and nutrient uptake, as well as survival, during transplanting.