Morphological diversity in breadfruit (Artocarpus, Moraceae): insights into domestication, conservation, and cultivar identification

Over millennia of breadfruit cultivation, hundreds of named cultivars have been developed that display a high degree of morphological diversity. The current study was undertaken to evaluate morphological diversity within the National Tropical Botanical Garden’s breadfruit germplasm collection, the largest and most diverse breadfruit collection in the world. A set of 57 standardized morphological descriptors including 29 leaf, 22 fruit, four seed, and two male inflorescence characteristics were used to describe and contrast 221 accessions of breadfruit including accessions of Artocarpus camansi Blanco, A. altilis (Parkinson) Fosberg, A. mariannensis Trécul, early generation A. altilis × A. mariannensis hybrids, and domesticated A. altilis × A. mariannensis hybrids. A morphological transition from heavily seeded fruit covered with flexible spines to fewer seeded, smoother skinned fruit of similar size was observed in the domestication of A. altilis from A. camansi. Further selection of true seedless, smooth-skinned cultivars of A. altilis appears to have occurred with human migrations from Melanesia into Polynesia. Cultivars from Micronesia exhibit morphological characteristics indicative of hybridization with the endemic species A. mariannensis. These data were used to generate a multi-access cultivar identification key on the Lucid platform that can be used to identify trees of known cultivars or to predict nearest cultivar relationships for previously undescribed cultivars. Overall, this study provides new insights into the morphological changes that occurred during domestication, helps visualize the diversity that exists across geographical regions, and provides a framework for cultivar identification and germplasm conservation.