Genetic variation in the endangered Florida torreya (Torreya taxifolia Arn.) and implications for conservation1

Torreya taxifolia Arn. (Florida torreya) is a critically endangered (International Union for Conservation of Nature 3.1) conifer with a very limited native range in the USA, occurring in two counties in Florida and one in Georgia where it persists in ravines along the Apalachicola River. The species suffered a major decline, ∼ 99% loss, beginning in the 1930s, with a total population estimated at 357,500 in the early 1900s decreasing to 1,000 individuals currently remaining in the wild. The initial decline was attributed to an unknown fungal disease with Fusarium torreyae (T. Aoki, J. A. Smith, L. Mount, Geiser and O'Donnell), identified in 2011 as the causal agent of a canker disease. The objectives of this work were to develop genetic markers to uniquely identify individuals, examine the structure of the in situ population, and use an ex situ germplasm resource to determine if reproduction without fertilization (apomixis) occurs. We developed a panel of microsatellite markers, sampled individuals from three natural in situ populations, and found population structure at all levels tested. The markers were next applied to ex situ mothers, potential fathers, and progeny to investigate the occurrence of apomixis. One of 29 progeny seedlings tested and its mother had identical multilocus genotypes. The probability of observing this genotype by chance, given the mother and the two possible fathers' genotypes, is approximately one in ten. Based on these data, we cannot reject the hypothesis that apomixis occurs. Our finding of population structure suggests genotypes from as wide an area as possible are required to capture the diversity of the species in conservation efforts. The multiplexed marker panel can be used to identify individual accessions and assist with managing ex situ collections; however, they are not informative enough to clearly differentiate closely related individuals in the ex situ population.