HEAT INHIBITION OF TUBER DEVELOPMENT IN POTATO (SOLANUM-TUBEROSUM L) - EFFECTS ON MICROTUBER FORMATION INVITRO

Microtuber formation by single node stem segments of in vitro grown potato plantlets was used as a model system for investigation of heat inhibition of tuber development. The stem segments were incubated in darkness at 20-degrees-C or 26-degrees-C on a tuberisation medium containing benzyl aminopurine (140 mug l-1) and sucrose (80 g l-1). Continuous incubation at 26-degrees-C strongly inhibited tuberisation and exposure to 26-degrees-C for only 1 week before transfer to 20-degrees-C significantly reduced microtuber fresh weight. Inclusion of a gibberellin synthesis inhibitor, paclobutrazol (10(-5) M), in the tuberisation medium counteracted the heat inhibition of tuber initiation but not the reduction of microtuber fresh weight. Thus, consistent with previous reports, inhibition of tuber initiation appears attributable to increased endogenous levels of gibberellins. Possible causes of the reduction in microtuber fresh weight are discussed.