Poor inflorescence development of 'Menindee Seedless' grapevines in the subtropics leads to low fertility

Tablegrape (Vitis vinifera L.) yield is lower in the subtropics than in Mediterranean production systems. To explain this difference, the development of inflorescence primordia of 'Menindee Seedless' grape in Emerald, Australia, one of the hottest grape-growing regions in Australia, was described using dissecting and scanning electron microscopy. Inflorescence initiation and branching occurred 42 and 70 days after budburst (Growth Stages 23 and 33 of a modified Eichhorn-Lorenz system, respectively). This period is 1-2 weeks earlier than under temperate conditions. From 70 to 268 days after budburst (leaf fall), only 44% of sample buds from nodes 4 to 6 of potential canes showed inflorescence primordia. It is concluded that the lower yield in the subtropics is due to low bud fertility, with disrupted inflorescence development associated to high summer temperatures.