|Manici, L. - Cra-Plant Pathology Research Institute|
|Kelderer, M. - Research Centre For Agriculture And Forestry Laimburg|
|Caputo, F. - Cra-Plant Pathology Research Institute|
Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2014
Publication Date: 7/7/2015
Citation: Manici, L.M., Kelderer, M., Caputo, F., Mazzola, M. 2015. Auxin-mediated relationships between apple plants and root inhabiting fungi: impact on root pathogens and potentialities of growth-promoting populations. Plant Pathology. 64:843-851.
Interpretive Summary: The immediate post-plant period is the time during which newly established fruit trees are most susceptible to biotic and abiotic stresses when planted on sites previously planted to the same or related crop species. Soilborne pathogens resident to these sites which is compromised primarily of a root rot fungal complex, actively attacks young roots causing root death. Thus, the ability to induce enhanced root proliferation of the rootstock in this system has significant potential to reduce the effect of the replant disease pathogen complex on tree growth and productivity. To date, bacteria and mycorrhizal fungi have been the most commonly reported organisms to possess a hormone-based root-inducing activity. There has been little study of the practical use of growth promotion abilities of endophytic fungi as a means to enhance crop development. The evidence reported in this study suggests that there exists potential for utilizing the rooting induction ability of hormone (indole acetic acid; IAA)-producing endophytic fungi as a means to develop cropping practices aimed at increasing soil health and soil suppressiveness in permanent cropping systems such as apple orchards. This strategy is consistent with the IAA production ability observed for most endophytic fungal isolates investigated in this study, as they are endemic to the replanted apple orchard soils. In particular, Fusarium acuminatum, the most promising species based upon its high IAA production and root inducing ability, was isolated frequently from apple roots. the significant increase in dry matter production of plants colonized by F. acuminatum obtained in plant bioassays, suggests that these fungi may represent one of the beneficial plant–microbe interactions responsible for high quality fruit production in several agro-environments.
Technical Abstract: Studies were conducted to examine the symbiotic relationship between plant hosts and endophytic fungi recovered in multi-generation replanted apple orchard soils. Based upon results obtained, subsequent studies were oriented toward investigating fungal populations showing a mutualistic symbiotic relationship with apple rootstocks. Symbiotic relationships of three groups of endophytic fungi (Ceratobasidium sp., Cylindrocaropon-like group and Fusarium acuminatum) with apple rootstocks were evaluated in plant growth bioassays. Auxin (IAA) and Gibberellins (GA3 and GA4) produced in fungal culture filtrates were evaluated as metabolites potentially involved in plant growth promotion. IAA-based functionality of F. acuminatum and other Fusarium spp. was evaluated using plantlets of apple rootstock grown on plant tissue culture medium supplemented with fungal culture filtrate. Cylindrocaropon-like group and Ceratobasidium sp. showed a symbiotic relation with the host plant varying from pathogenic to commensal, while that of F. acuminatum varied from commensal to mutualistic. IAA produced by fungal isolates was positively correlated enhanced plant growth observed in bioassays. This was further demonstrated by rooting induction observed on vitroplants. Findings of this study suggest that there exists potential for utilizing the root-inducing behavior of IAA-producing endophytic fungi endemic in replant orchard soils to enhance apple growth.