Physiological characterisation of coprophilous fungal isolates that behave as plant root associates

Abstract

Different fungal isolates closely related to Zopfiella erostrata and Cercophora caudata have been found to colonise plant root tissues in an asymptomatic way in the Monte Desert biome of La Rioja Province, Argentina. This interaction has been newly discovered, and the role of these fungi in their desert habitat has never been studied in detail. The objective of this study was to evaluate eight fungal isolates by means of specific physiological traits that could have implications for their interaction with the host plant. The selected isolates, four endophytic and four rhizospheric, were characterised for their ability to produce indole acetic acid, solubilise and mineralise phosphorus (P), and utilise different nitrogen sources. In addition, we evaluated organic acid production and phosphatase activities as mechanisms of P recycling. These analyses revealed that most isolates produced indole acetic acid, and that all isolates could solubilise and mineralise P, although to different degrees. Furthermore, the production of organic acids correlated with P solubilisation levels, which may enhance P availability in soils. Nitrogen utilisation was variable among the isolates, without specific patterns concerning the different sources and fungal isolates tested. Our results demonstrated that the fungal isolates had great variability, probably because they complete their teleomorphic phase in their habitats, generating viable meiotic spores, in addition to the active dispersion of these fungi by the underground rodent Ctenomys aff. knightii from which they were isolated. Although the isolates were variable, the endophytic isolates exhibited improvement in all the P parameters measured. This can be explained by the ability of these isolates to intimately colonise root tissues, while the colonisation by rhizospheric isolates is produced superficially in the rhizoplane. The high occurrence of this interaction, as well as the physiological traits detected, suggest that this kind of fungi could play an important ecological role in the Monte Desert environment, benefiting the establishment and growth of new seedlings in areas occupied by the rodents.