Identification of mangosteen ancestors (Garcinia mangostana L. var. mangostana) via leaf anatomy and genome size analyses [EMBARGOED]

Abstract

Mangosteen (Garcinia mangostana L. var. mangostana) is a well-known tropical fruit that is majorly cultivated in Southeast Asia. The studies of mangosteen ancestors are still continuous, providing results that are interrelated with other Garcinia species. The previous studies of mangosteen ancestors focus more on morphological parts and genetic relationships with other related Garcinia species. Until now, the reports concerning mangosteen with its possible ancestors regarding anatomy and genome size are still limited. The genome size of one of the mangosteens possible parents, Garcinia celebica, is not available yet. This study aims to identify the possible ancestors of mangosteen based on leaf anatomical and genome size variation with Garcinia mangostana var. malaccensis and G. celebica. The leaf anatomical study encompassed the methods of leaf peeling, leaf venation, leaf cross-section, and scanning electron microscopy (SEM). The assessment of the leaf anatomy found that these three Garcinia species showed notable similarities, including paracytic and hypostomatous stomata, straight to wavy anticlinal wall, the presence of collenchyma cells, druses, mucilage canals, thick cuticular wax, petiole vascular bundle and, swollen tracheids. Meanwhile, leaf anatomical variations were observed, including midrib vascular bundle, sclerenchyma cells, tanniferous idioblast, leaf marginal outline, leaf marginal and laminal venation and the types of epicuticular waxes. Based on the cluster analysis using a Multivariate Statistical Package (MVSP), mangosteen and G. mangostana var. malaccensis were clustered together in the first node, showing the highest similarity index at 0.667. Meanwhile, mangosteen and G. celebica provided 0.500 similarity. The anatomical characteristics of mangosteen were intermediate between G. mangostana var. malaccensis and G. celebica, showing that these three Garcinia species are closely related. For flow cytometry, by using Glycine max cv. polanka (2C = 2.5 pg) as a standard, the genome size of G. celebica was found to be 4.27?0.38a pg. Based on one-way ANOVA and Tukeys test, there was a significant difference between mangosteen and its possible ancestors at the interspecific level, with the P value less than 0.05. Mangosteen had a significantly larger genome size (6.00?0.17b pg) than either of their potential parents, G. mangostana var. malaccensis (4.87?0.91a pg) and G. celebica (4.27?0.38a pg). The variations in genome size in this study indicated that possible interspecific hybridisation occurred between G. mangostana var. malaccensis and G. celebica, resulting in mangosteen as the interspecific hybrid. This study combined leaf anatomical characteristics and genome size variation, suggesting that G. mangostana var. malaccensis and G. celebica are the possible ancestors of mangosteen.