Development of an in vitro hydroponic system for studying the interaction between banana plantlet and Fusarium oxysporum f. sp. cubense

Abstract

Fusarium wilt of banana, caused by Fusarium oxysporum f. sp. cubense (Foc), is one of the most destructive diseases of banana. Several experimental systems have been used to study banana—Foc interaction, including pot system and hydroponic system. In this study, an in vitro hydroponic system was developed for the growth of rooted banana plantlet. It was characterized by a filter-paper holder, which consisted of a cone cup and a round tube. Besides being used as supporting material and providing nutrients to the banana plantlet, the filter-paper holder was designed to create a humid and aerobic environment for root growth. It was observed that rooted plantlet could grow normally in inoculum-free nutrient solution for at least 8 weeks. In the following rejuvenation experiment, each plantlet was back-inoculated by adding spore suspension of a degenerated strain of Foc tropical race 4 (TR4) into nutrient solution. Three to four weeks after in vitro inoculation, the rejuvenated strain was isolated from the rhizome of the plantlet showing symptoms under sterile conditions. The results of pathogenicity test indicated that the third-generation rejuvenated strain had partially regained virulence, which was characterized by lower radial growth rate and higher level of sporulation compared with the degenerated strain. In contrast to previously reported hydroponic systems which applied to studies in relation to Fusarium wilt of banana, the one described here is a totally closed system. It is demonstrated that the in vitro hydroponic system can be used for studying the interaction between banana plantlet and Foc TR4. A novel in vitro hydroponic system is described, in which a rooted banana plantlet can grow normally for at least 8 weeks without an air pump. In vitro inoculation technique allows banana plantlet—Foc interaction without interference of other microorganisms.