Effects of environmental variables and cropping on leaf conductance of custard apple (Annona cherimola x Annona squamosa) 'African Pride'

Diurnal variations in leaf conductance (g) were investigated in bearing and non-bearing custard apple (<i>Annona cherimola</i> x <i>Annona squamosa</i>) trees, cultivar 'African Pride', in subtropical Queensland, Australia (latitude 27°S). Most of the variation in log g could be attributed to changes in relative humidity (<i>RH</i>) (<i>R</i>² = 0.86, <i>P</i> < 0.01). At <i>RH</i> < 60%, g was extremely low (< 0.4 cm s^-1). The marked sensitivity of custard apple stomata to <i>RH</i> suggests that CO₂ assimilation could be dramatically reduced at low <i>RH</i>, and this may be one of the explanations for the poor fruit size of this cultivar. Although there were no significant differences in g on non-fruiting terminals of either bearing or non-bearing trees, the g of leaves adjacent to fruit was ∼ 20% lower than leaves on non-fruiting terminals at similar nodal positions. The productivity of custard apple in the field could be improved by techniques which raise <i>RH</i>, such as the use of windbreaks and overhead intermittent misting.