Inoculation with Ericoid Mycorrhizal Fungi Alters Root Colonization and Growth in Nursery Production of Blueberry Plants from Tissue Culture and Cuttings

Abstract

In nursery production, inoculation with mycorrhizal fungi is thought to be most beneficial when colonization occurs as early as possible during plant growth. Unrooted tissue culture plantlets (TC) and hardwood cuttings (HC) of different cultivars of highbush blueberry plants (Vaccinium corymbosum L.) were inoculated with mixed inoculum of three different isolates of ericoid mycorrhizal fungi (EMF) in a commercial blueberry nursery. Plants were monitored for root colonization by EMF and plant growth to determine if inoculation with EMF influences rooting, subsequent plant growth, or EMF colonization during one (HC) or two (TC) years after inoculation. Tissue culture plants became naturally colonized by EMF, however, the intensity of this natural colonization was low and inoculation with EMF increased colonization for some cultivars, especially in the first few months after inoculation. This suggests that low colonization during nursery production of blueberry may be at least partially a result of low inoculum potential of the growing medium. However, we found that the frequency and intensity of colonization of certain cultivars decreased substantially after plants were transplanted and moved to an outside growing area. This decrease in colonization suggests that; (1) the fungi used for inoculation may not be suitable for this cultivar under the specific cultural conditions used in the nursery, (2) changes in cultural conditions from transplanting inhibited further colonization of the fungi that were present in the initial stages of propagation, or (3) there were possible changes in the type of fungi on the root system. Inoculation of TC plants with EMF caused measurable changes in root and aboveground plant morphology and biomass partitioning during the first two growing seasons; however, we found that the responses to inoculation with EMF can vary with cultivar, suggesting that a level of plant-fungus specificity may exist in EMF associations with blueberry plants that influences plant growth. Inoculation of HC with EMF increased colonization frequency and intensity on cuttings under the cultural practices used in the nursery; however, colonization decreased between 3 months and 5 months after sticking suggesting that the specific cultural conditions used during propagation decrease colonization by both natural and inoculated populations of the fungi. Even though colonization decreased during propagation, inoculation reduced the time required for rooting and caused measurable changes in root biomass of rooted cuttings. This increased root biomass may lead to increased quality and performance of rooted cuttings after transplanting.