Silver compounds regulate leaf drop and improve in vitro regeneration from mature tissues of Australian finger lime (Citrus australasica)

Abstract

Finger lime is a small-leaved citrus native to Australia that is becoming increasingly popular worldwide. Finger lime is monoembryonic and cannot be propagated true to type from seeds. Initial studies to develop a tissue culture protocol for the mass production of elite lines being developed in our breeding program were unsuccessful due to complete leaf abscission during the culture establishment phase. In this study, silver-containing compounds such as silver thiosulfate (STS), silver nitrate (AgNO3), and silver nanoparticles (AgNPs) were applied at three concentrations (20, 40, and 60 µM) to manage ethylene biosynthesis in finger lime tissue cultures. The Murashige and Skoog (MS) medium supplemented with 2.2 µM BAP and 60 µM silver thiosulfate was the best medium for culture establishment. The same level of STS with 0.70 µM GA3 produced the largest number of shoots and prevented leaf abscission. Micropropagated shoots were successfully rooted in half-strength MS medium supplemented with 0.10 µM NAA. The addition of 60 µM silver thiosulfate (STS) to the MS medium resulted in efficient micropropagation of the finger lime explants and controlled leaf abscission. The study evaluates the efficacy of various silver-containing compounds on their ability to effectively control ethylene production and allow for the development of an efficient tissue culture protocol for Finger lime.