Enhanced Morphological and Physiological Responses of Micro-propagated Cassava Through Arbuscular Mycorrhizal Fungus Inoculation

Abstract

Micropropagation is instrumental for the rapid multiplication of elite cassava varieties with improved traits. However, it is often impaired by transplanting stress associated with acclimatization, which occurs during the acclimatization, transfer from in vitro to soil condition. Arbuscular Mycorrhizal Fungi (AMF) could be used to reduce transplant shock symptoms through improved nutrient acquisition and physiological function. In this study, we investigated the impact of inoculating an AMF, R. irregularis, on the growth of two varieties of micropropagated cassava on plant physiological traits, the δ 13C and δ 15N isotopic signatures , and nitrogen use efficiency (NUE) during acclimatisation. In the early acclimatization stage, (4-8 weeks after transplanting, WAT), AMF inoculation increased height, stem diameter, and leaf number by 61%, 50%, and 57% respectively, compared to non-inoculated plants in non-sterile soil. Under subsequent water deficit at 8-10 WAT, inoculated plants were better preserved regarding height and stem thickness. After 10 weeks, AMF root colonisation increased by 57% and 61% under water-deficit and well-watered conditions respectively, compared to non-inoculated plants. Total biomass, C:N and NUE increased significantly in inoculated plantlets under well-watered conditions, with lowered δ 15N and N concentrations due to N dilution from a 63% biomass increase. In water-deficient conditions, regardless of inoculation, δ 13C decreased, suggesting the dominant role of water availability in carbon assimilation. Overall, we found important benefits of AMF inoculation. Yet, to fully harness the benefits of AMF for micropropagated cassava, proper nitrogen management is essential, as the enhanced growth conferred by increased root colonisation rate could lead to N deficiency.