Three-dimensional virtual flower bud of walnut tree based on micro-computed tomography

Walnut (Juglans regia L.) is one of the most widely cultivated and high-yielding tree nut in temperate areas. In-depth study of walnut flower bud structure has important practical applications for early determination of flower bud's quality and to promote scientific production guidance. The flower buds of walnut tree were scanned by micro-computed tomography (Micro-CT) and the three-dimensional (3D) virtual flower buds of the same were reconstructed based on the scanned images. The reconstructed flower buds exhibited the shape, size, exterior characteristics, and internal structure clearly as that of real walnut flower buds, including scales, leaf primordia, bracts, and female floral primordia from out- to inward. The results showed that the female flower bud had nine scales, seven leaf primordia and two female floral primordia. The male flower buds are pinecone-shaped and contain multiple male flowers. Each male flower is divided into bracts, calyx, and stamens from outside to inside. Our study showed that the Micro-CT could achieve the 3D visualization of walnut flower buds, and could also create videos of the virtual observation of fruit tree flower buds, providing an effective way for digital flower bud construction.