MORPHOLOGICAL AND PHYSIOLOGICAL SCREENING OF ETHYL METHANESULFONATE-TREATED SUGARCANE CALLI AND PLANTLETS FOR In vitro MANNITOL-INDUCED OSMOTIC STRESS TOLERANCE

Sugarcane production in South Africa is limited by drought stress and its impact is expected to increase due to climate change. However, limited research is conducted to develop cultivars that are suitable for cultivation under water-stressed conditions. This study aimed to select, through morphological and physiological traits, the ethyl methanesulfonate treatment(s) that can produce calli and plantlets that are resistant to mannitol-induced osmotic stress. Sugarcane calli were exposed to ethyl methanesulfonate for 0.5, 1, 2, and 3 hours. To determine optimal selection lethal doses, calli were cultured on media containing 0, 150, 225 and 300 mM mannitol for further eight weeks under dark and light conditions. Incubation periods of half an hour and one hour induced genomic mutations without inhibiting callus growth and plant regeneration abilities. EMS-treated calli retained whiter, compact and with yellowish friable texture when compared with the control after the two-weeks recovery period post exposure to osmotic stress. Callus that was exposed for one hour was able to recover and regenerate plantlets at 225 and 407 mM mannitol stress. However, the two-hour incubation period and above resulted in stunted and albino plantlets. The LD50 and LD90 for selection were calculated as 225 and 407 mM mannitol. The EMS mutagenesis and in vitro selection for osmotic stress using mannitol can be used successfully to select sugarcane plantlets with better morphological and physiological responses to water stress in a very short time.