Genetic data confirms field evidence for natural breeding in a wild taro population (Colocasia esculenta) in northern Queensland, Australia

Taro (Colocasia esculenta) is a vegetatively propagated, starchy root crop cultivated in tropical to temperate regions of the world. Wild forms of taro are distributed from India to southern China, Australia and Melanesia. They are widely known wild food or fodder sources, including in Aboriginal Australia, so it is unclear to what extent wild populations have been dispersed by humans, or naturally via insect-borne pollen and seed dispersal by birds or other animals. In Australia, pollinators and seedlings of taro have not been reported, and a key question is whether or not the wild taro there can breed naturally. Here we report field observations of flowering, fruit set, and an insect pollinator (Colocasiomyia, pupal stage), in a historically significant wild taro population at Hopevale in northern Queensland. The observed pupa is congeneric with two pollinating fly species that have a highly specialised, probably coevolutionary, relationship with taro in neighbouring Papua New Guinea. The field observations suggested the possibility of natural breeding at Hopevale. By analyzing microsatellite diversity within the Hopevale taro population, we found high genetic variation overall, indicative of multiple founding individuals. Two sublocations showed low genetic diversity and strongly negative inbreeding coefficients, consistent with predominantly clonal (vegetative) reproduction. A third sublocation showed high genetic diversity and a weakly negative inbreeding coefficient, indicative of sexual reproduction. This difference between sublocations may relate to microenvironmental conditions that favour seedling establishment in some parts of the site. The data constitute the first demonstration that natural breeding and population spread occurs in Australian wild taro.