Getting ready for outdoors: Biohardening boosts banana plantlet performance and induced resistance to Fusarium wilt (Subtropical Race 4)

The use of beneficial microorganisms during the acclimatization of micropropagated plants represents a promising biotechnological tool to improve plant establishment and enhance protection against soil pathogens under field conditions. This study explores the potential of a mycorrhizal-based inoculant in biohardening to boost banana plants performance and prime disease resistance. The effects of inoculation during the acclimatization of in vitro-propagated banana plantlets on plant development and resistance against Fusarium oxysporum f. sp. cubense Subtropical Race 4 (Foc-STR4) were evaluated. Biohardened plants exhibited enhanced early growth (greater shoot and root development). Moreover, biohardening lead to a strong reduction in disease symptoms (corm necrosis, leaf size and pseudostem diameter) and pathogen proliferation in roots and soil, and improved nutritional status (higher NPK levels) in Foc-STR4 challenged plants. Molecular analyses revealed a primed defense response in the biohardened plants, characterised by an increased accumulation of the defense related hormone salicylic acid and its glucosylated form, alongside with a stronger induction of defense-related genes associated with oxidative stress and jasmonate signalling. Overall, the results reveal that biohardening of micropropagated banana plants with the mycorrhizal inoculant enhances plant performance and primes defense responses, thereby mitigating Fusarium wilt. This study highlights the potential of biohardening strategies for the sustainable protection of micropropagated crops of high agronomic value.