Development of morphological marker on natural interspecific hybrid seedling of Acacia (Acacia mangium × Acacia auriculiformis) verified by molecular marker

Development of the hybridization between two different species of Acacia mangium and Acacia auriculiformis in Indonesia started in 2009 by establishing an open-pollinated orchard to produce the natural Acacia hybrid seed in Wonogiri District, Central Java Province. The design of the orchard was an alternate row between A. mangium and A. auriculiformis with a spacing of 5 × 5 meters. The orchard produced putative Acacia hybrid seeds firstly in 2013. Based on flowering synchronization between the two species, seeds from 38 sample trees of A. mangium were taken to identify their character seedling morphology to obtain the Acacia putative hybrid. The seedling morphological characteristics observed were leaf development patterns from the emergence of a true leaf (pinnate) until the pseudo leaf (phyllode) emerged. Acacia putative hybrid was then verified using a Simple Sequence Repeat (SSR) marker and Sequence Characterized Amplified Region (SCAR) to obtain the hybrid of A. mangium × A. auriculiformis. The result showed that the presence of 4-pinnate on the seedling development pattern was verified as 100% pure species of A. mangium and the opposite was 100% hybrid. In comparison, the presence of a true leaf of phyllode + 4-pinnate was verified as a 40% hybrid. The final estimation of Acacia hybrid seed production at the hybrid seed orchard on the first flowering was about 3.1% approximately based on the seedling leaf development pattern.