Regeneration of Sesuvium portulacastrum through Indirect Shoot Organogenesis and Influence of an Endophytic Fungus on Rooting of Microshoots

Sesuvium portulacastrum L. is a dicotyledonous halophyte belonging to the family Aizoaceae. Its young leaves are highly nutritious, and many ecotypes are used as leafy vegetable and medicinal crops. Additionally, due to their tolerance to soil salinity, flooding, and high temperatures, some ecotypes are used for the remediation of saline soils. As a result, there is an increasing need for a large number of disease-free S. portulacastrum propagules. This study developed an efficient protocol for the regeneration of S. portulacastrum through indirect shoot organogenesis. Leaf explants were cultured on Murashige and Skoog basal medium supplemented with different concentrations of zeatin (ZT) and indole-3-acetic acid (IAA). Callus was induced in all explants cultured with 1.5 mg/L ZT only or 1.5 mg/L ZT with 0.5 mg/L IAA. The callus was cut into small pieces and cultured on the same medium on which it was initially induced. ZT at 1.5 mg/L induced 73.7% of callus pieces to produce adventitious shoots, and the shoot numbers per callus piece were up to 20. To improve the in vitro rooting of adventitious shoots, commonly known as microshoots or microcuttings, an endophytic fungus, Cladosporium ‘BF-F’, was inoculated onto the rooting medium. ‘BF-F’ substantially enhanced rooting and plantlet growth, as the root numbers were three times more and plantlet heights were 70% greater than those without ‘BF-F’ inoculation. To detect the genes involved in the enhanced rooting and plantlet growth, qRT-PCR analysis was performed. Results showed that genes related to auxin responses and nitrogen uptake and metabolism were highly upregulated in ‘BF-F’-inoculated plantlets. Plants inoculated with ‘BF-F’ grew vigorously after being transplanted into a sand–soil substrate. Thus, this study not only established an efficient protocol for the regeneration of S. portulacastrum but also developed a novel method for improving the rooting of microshoots and plantlet growth. The established propagation system could be used for producing a large number of S. portulacastrum plantlets for commercial use and also for genetic transformation.