GREENHOUSE WARMING AND VERNALIZATION OF HIGH-CHILL FRUIT IN SOUTHERN AUSTRALIA

Most deciduous fruit trees need sufficient accumulated chilling, or ve rnalisation, to break winter dormancy. Inadequate chilling due to enha nced greenhouse warming may result in prolonged dormancy, leading to r educed fruit quality and yield. The potential impact of warming on chi ll accumulation has been analysed using the Utah vernalisation model a nd temperature data from over 400 climate stations in southern Austral ia. Two experiments were performed: (i) a sensitivity study where temp eratures were increased at all sites by either 1, 2 or 3 degrees C; (i i) a scenario study for the year 2030 where temperatures were increase d according to spatially- and seasonally-varying warming scenarios der ived from five global climate models under enhanced greenhouse conditi ons. The sensitivity study shows that warming causes greater reduction in chilling at sites with a higher present mean temperature and/or a wider diurnal temperature range. In the scenario study, two warming sc enarios for the year 2030 were considered: a low (high) warming scenar io which assumes a low (high) rate of increase of greenhouse gas emiss ion, a low (high) global climate sensitivity to increased emissions, a nd a low (high) regional temperature response. The low warming scenari o is less than 1 OC in southern Australia and is unlikely to affect th e vernalisation of high-chill fruit, except for pome-fruit grown in so uth-west Western Australia. The high warming scenario exceeds 1.5 degr ees C and would significantly increase the risk of prolonged dormancy for both stone-fruit and pome-fruit at many sites.