Colonisation Dynamics of Arbuscular Mycorrhizal Fungi and Dark Septate Endophytes in the Sugarcane Crop Cycle

The root systems of sugarcane (Saccharum L. spp. hybrids) host a variety of symbiotic fungal organisms including arbuscular mycorrhizal (AM) fungi and dark septate endophytes (DSE). Characterisation of the temporal dynamics of AM/DSE colonisation in sugarcane sett and adventitious shoot roots following ratooning is required to enable further research into AM/DSE symbiosis in sugarcane crops. This study investigated the colonisation dynamics of AM/DSE within sugarcane root systems in 1^st and 2^nd ratoon phases. A field study was undertaken at two proximal sites with different cropping histories to assess AM/DSE colonisation of sugarcane sett and shoot roots over 28 weeks of crop development. At each observation, the functional structures formed by AM (arbuscules, hyphae, spores and vesicles) were delineated and quantified. Significant differences in the rate of AM/DSE colonisation over time and between root types were observed. There were no significant differences in AM sett root colonisation between sites. For both fungal types, differences in shoot root colonisation between sites were not significant. Levels of DSE sett root colonisation were significantly lower in the 2^nd ratoon compared to the 1^st ratoon crop. For both fungal types, sett root colonisation was significantly higher than for shoot roots at both sites. Maximum colonisation levels of AM/DSE in sugarcane sett roots occurred between 5–7 weeks, prior to the establishment of shoot roots and rapid development phase of ratoon crops. While AM colonisation levels within sett roots were maintained across ratoon phases, there is a need to account for the differences in DSE colonisation levels between 1^st and 2^nd ratoon crops. These data provide the basis for the design of sampling strategies in future studies investigating management impacts on AM/DSE in sugarcane cropping systems.