Forgetting cane grasses: Switching temporal focus to reveal mosaics of Saccharum diversity

Abstract

Sugarcane (Saccharum cvs.) is one of the most important cash crops globally. Related varieties and species of cane grasses of the genus Saccharum are also important subsistence crops in the Indo‐Pacific region. Despite the significance of these crops globally and recent advances in genetic characterisation, the histories and geographies of domestication are poorly understood. A scenario for the geodomestication of sugarcane is proposed to highlight the diversity of Saccharum species and their significance for future proofing sugarcane. The historical agrobiodiversity of cane grasses, together with practices of cultivation, uses and associated forms of practical and symbolic knowledge, provide culturally appropriate bases for crop improvement.An historical scenario for the domestication of sugarcane (Saccharum cvs.) is proposed based on a literary review of a range of agronomic, archaeobotanical, archaeological, genetic, historical, linguistic and phytogeographic sources. The proposed scenario outlines a protracted, multistage domestication process for the extended period before the directed breeding programmes that led to the development of modern commercial cultivars over the last 100 years or so. First, the initial management, cultivation and translocation of Saccharum robustum within the circum‐New Guinea region produced cultiwilds (viz., morphogenetically wild plants cultivated and translocated by people) and, arguably, some S. robustum cultivars. Second, the spontaneous generation of sugar‐rich pith in some S. robustum plants and subsequent anthropic selection led to the development of ‘domesticated’ Saccharum officinarum within the circum‐New Guinea region. Third, the dispersal under cultivation of S. officinarum cultivars brought them into contact with wild‐type Saccharum spontaneum populations around the Indo‐Pacific, which led to the development of sugarcane (S. officinarum × spontaneum) hybrids that were subsequently cultivated and selected vegetatively. These ancient hybrids Saccharum barberi and Saccharum sinense became regionally important in India and China, respectively.Although much research has focussed on clarifying the Saccharum lineages directly contributing to the major commercial sugarcane cultivar lineages, such a teleological interpretation misses a vast range of agrobiodiversity in terms of the plants (S. robustum, S. officinarum, S. barberi, S. sinense and S. cvs.); domestication status (wild, cultiwild and domestic); and, practices (associated with cultivation, use and traditional knowledge) in the past. The diversity of plants and practices in the past provides the historical backdrop against which any linear interpretation of sugarcane domestication should be understood. This historical reconstruction of domestication processes draws attention to this agrobiodiversity, which can inform breeding programmes seeking to diversify and improve sugarcane cultivars for commercial and subsistence agriculture into the future.