EFFECT OF ETHYLENE AND CULTURE ENVIRONMENT ON DEVELOPMENT OF PAPAYA NODAL CULTURES

Papaya (Carica papaya L.) nodal cultures modified the atmosphere of th e headspace of the vessel used for culture maintenance by producing et hylene. Under culture maintenance nodal cultures grew poorly and leave s senesced. Incubating nodal cultures under a range of ethylene concen trations suggested that this poor performance was caused in part, by t he production of ethylene and its accumulation in the headspace of the vessel. To further evaluate the role of ethylene accumulation in grow th suppression, aminoethoxyvinylglycine (AVG), 1-aminocyclopropane-1-c arboxylic acid (ACC) and silver thiosulphate (STS), were added to the nutrient medium and ethylene measurements performed during culture gro wth. The ethylene-suppressant, AVG, (1.2 mu M) and the ethylene-antago nist, STS, (0.3 mM) significantly improved nodal culture growth (283 a nd 289% respectively), leaf area production (350 and 211% respectively ) and reduced leaf senescence, while the ethylene-precursor, ACC, (1.5 mM) significantly decreased culture growth (71%), leaf area productio n (88%) and promoted leaf senescence. Furthermore, nodal culture growt h was significantly better at 20 degrees C than 30 degrees C since eth ylene production and accumulation were less in these conditions. Bette r control or management of ethylene accumulation produces healthier no dal cultures for micro-propagation and may be a way of improving produ ctivity of other papaya shoot culture systems.