Reduction in hyperhydricity and improvement in in vitro propagation of commercial hard fibre and medicinal glycoside yielding Agave sisalana Perr. ex Engelm by NaCl and polyethylene glycol.

Agave sisalana is hapaxanthic monocotyledonous plant yielding a hard fibre of commercial value. It is also a source of medicinally important glycosides such as hecogenin and tigogenin. Sisal plantations can play a significant role in reforestation of hilly barren land. Unfortunately, natural propagation is not sufficient to fulfill the demands; besides, hyperhydricity is a severe problem in the in vitro propagation method of A. sisalana. The present study for the first time demonstrates that, the hyperhydricity problem can be solved by inclusion of osmotic stress inducing agents like sodium chloride (NaCl) and polyethylene glycol (PEG 6000) (0.0, 0.1, 0.2, 0.3, 0.4, or 0.5% w/v) in MS medium. The response of hyperhydric shoots, normal shoots and hyperhydric reverted shoots with the treatments was analyzed for water content, chlorophyll content, osmolyte accumulation and oxidative damage. The principal component analysis showed the significant positive and negative variations in the net photosynthesis, stomata conductance, internal CO₂, transpiration, and water use efficiency between normal, hyperhydric and hyperhydric reverted shoots among all the time points of day and night period. Besides, detailed anatomical and ultra-structural observations were made to discern the changes that occurred in epidermis, mesophyll cells, vascular bundles, and stomata. About 85 and 58% of hyperhydric shoots were reverted on medium fortified with 0.2% NaCl and 0.1% PEG, respectively. All reverted shoots were normal and survived when transferred to the field conditions. The improved protocol with the treatment of NaCl for recovery of hyperhydric shoots was not cost intensive and without any harmful effects on shoots and plantlets. Key message: First report on change in physiology and recovery of hyperhydricity with NaCl and PEG in shoots and somatic embryos of Agave sisalana which allows additional 38% plantlets available for plantation. [ABSTRACT FROM AUTHOR]