Assessment of genetic diversity of the invasive Callery pear, Pyrus calleryana Decne. using mitochondrial microsatellites and its molecular detection using LAMP

Pyrus calleryana Decne. (Callery pear; [PC]) is a popular ornamental tree in the urbanized areas of the United States of America (US), owing to its aesthetical value, with showy white blossoms in early spring and vibrant fall foliage. The tree native to Asia is now becoming one of the most problematic invasive tree species in the eastern US. From its introduction in the early 20^th century, PC has been commercially used as rootstocks for propagating fruiting pears, alongside other closely related pear species. Several states are restricting the sale of rootstocks to limit the ongoing spread of PC. As such, there is a need to study the genetic diversity of PC and develop a field-based detection tool that can reliably detect PC rootstocks. For the first study, we identified candidate region in nuclear genome of PC and developed a rapid, sensitive and specific loop-mediated isothermal amplification (LAMP) assay to successfully detect invasive PC DNA and to differentiate it from the DNA of three closely related species, namely P. communis, P. pyrifolia, and P. betulifolia. The LAMP results were obtained within 30 minutes of incubation at 65 ℃. The development of a LAMP assay for detecting invasive PC is a pivotal advancement in the management of invasive species. For the second study, we developed mitochondrial genome and five microsatellite markers localized therein, to analyze genetic diversity of Asian population, Southeastern escapees (SNesc), Tennessee escapees (TNesc), and US-released commercial cultivars (UScult). 72 specimens of Asian PC, 67 samples of the UScult, and 180 samples from SNesc/TNesc population were analyzed. Our data revealed high genetic diversity (H_e = 0.842) and presence of genetic structure in PC. The results indicated the possibility of divergence of TNesc from Asian population, and SNesc and UScult from TNesc. The observed high genetic diversity among PC cultivars illustrates the intricate genetic landscape shaped by multiple factors, including potential, highly likely unintended, mislabeling of the US-released cultivars. This study underscores the need for broader genomic studies to further elucidate the genetic architecture of cultivated PC composition and supports the development of robust method for cultivar truthing and invasion management.